Starting seeds in perlite

Contents

Perlite – How useful it can be in your Gardening Job!

Perlite is the name for a naturally occurring siliceous rock. When heated, it has the capacity to expand from four to twenty times its original volume. This is due to the rapid expansion of water within perlite, which creates the extremely light perlite that we use for gardening.
The main function of perlite for the gardener is to aid water retention and aeration as well as improve compost mixtures.
Perlite is mined and expanded all over the world. The United States is estimated to be the largest consumer and producer of both crude and expanded perlite. However, other countries producing perlite include China, Greece, Japan, Mexico, Hungary, Armenia, Italy and Japan.
Benefits

  1. Prevents compaction
  2. Improves aeration and drainage better than vermiculite
  3. Stimulates root initiation and vigorous growth
  4. Holds moisture but does not become soggy
  5. Almost neutral pH
  6. Does not decompose
  7. Free from disease, weeds and insects
  8. Insulates and minimises temperature fluctuations
  9. Inorganic, inert and sterile
  10. No known toxicity or fire hazard

Uses of Perlite
Seed Germination
Perlite speeds up germination and improves seedling growth.
For seeds, sow on a well-watered mixture of equal parts perlite and Sphagnum Moss Peat. Alternatively, add 1 part perlite to 2 parts ready-mixed potting compost.
For use pure, keep wet at all times by capillary irrigation or intermittent mist. After sowing, sprinkle seeds with a thin layer of fine peat and cover with glass or plastic to retain moisture until germination, then feed
Potting Mixes
Perlite is used in potting compost mixes to improves aeration, draining and insulation. Perlite can be used to open up the structure of ready-mixed loam or peat-based composts.
For soilless compost mixtures, use 3 or 4 parts of Sphagnum Moss Peat to 1 part of perlite (80/20).
For loam-based compost mixtures, use equal parts sterilised loam, peat and perlite (1:1:1) plus limestone and nutrients. Alternatively, a 1:2:1 mix may be used. Mix thoroughly, then water well after planting and feed as appropriate.
Rooting and Cuttings
Perlite speeds up rooting, reduces risk of damping off, provides an optimum balance of air and water, and makes water logging almost impossible. It also minimises damage to roots and growth disruption from transplanting.
For soft stem and leaf cuttings, use a mixture of equal parts perlite and Sphagnum Moss Peat (50/50). For harder cuttings and fragile plants, increase the proportion of perlite up to 4 parts perlite to 1 part peat (80/20).
For mist irrigation, perlite may be used 100% where sterility is essential. Keep well-watered but ensure free drainage. Feed plants as soon as roots develop.
Soil Conditioning
Perlite improves the texture of heavy silt or clay soils by increasing aeration and drainage. It also minimises the tendency to ‘cap’ over germinating seeds. These improvements will last for many years.
For difficult seed beds and flower beds, use up to 25% perlite worked into the top 5-10cm before sowing.

For trees, shrubs and roses, mix perlite with the soil when back-filling the planting hole to stimulate root growth.
Turf Dressing
Because Perlite improves aeration and drainage, it will assist the air-moisture balance and ensure better root development and turf growth. Golf course greens treated with perlite will show improved resilience and greater tolerance in use under extreme weather conditions – wet or dry.
For compacted and poorly drained areas on old turf and for establishment of new turf, use as follows: Spike over the affected area with a hollow tine, then spread a thin layer (2-5mm) of damp perlite pre-mixed with a suitable fertiliser. Rake or brush evenly, and water thoroughly. Note: a 100-litre bag of perlite will give on average a 2mm layer over 50sqm
Capillary Watering, NFT & Hydroponics
Perlite is an inert, sterile, neutral, ultra-lightweight aggregate with a very high air and water-holding capacity. To sterilise perlite for re-use, steam, flame-gun or treat with any proprietary chemical steriliser.
For capillary watering use, allow at least 25mm (1 inch) depth of perlite in place of sand or gravel in polythene-lined benches or suitable trays.
For ring culture and low cost commercial production of tomatoes, use perlite in a polythene lined trench or channel, and saturate with nutrient solution.
Special Note:
With electrical heating cables use a 50/50 mix of perlite and sand to prevent overheating.

Whether you’re planning for spring or just getting a head start on your gardening tasks in general, starting seeds can be one of the trickiest parts of being a gardener.

If you’re used to buying seedlings from your local nursery and haven’t started seeds before, it can be daunting to figure out exactly what type of seed starting mix is best.

In this article, I’ll get into exactly what you need to know when choosing the best seed starting mix for your garden and seedlings.

If you just want my top recommendations, check them out below.

Best Organic Seedling Mix Best for Hydroponics Espoma SS16 16-Quart Organic Seed Starter Premium Potting Mix General Hydroponics Rapid Rooter Replacement Plugs 50 count Best Organic Seedling Mix Espoma SS16 16-Quart Organic Seed Starter Premium Potting Mix Best for Hydroponics General Hydroponics Rapid Rooter Replacement Plugs 50 count

Other Good Options:

  • Black Gold Seedling Mix, 16qt
  • Hoffman Seed Starting Soil, 10qt
  • Jiffy Organic Starter Mix, 16qt

What is Seed Starting Mix?

Although the name sounds fancy, a seed starting mix is simply a specific mixture of soil that is designed to give seeds their best chance at germinating and growing into healthy young seedlings.

Seed mixes are typically finer and lighter than typical garden potting soil, making them easier for young roots to navigate.

What is a Soilless Seed Starting Mix?

When I first started gardening, I was confused by soilless seed mixes. How could a plant grow without soil?

It’s a reasonable question, but what I didn’t realize is that seeds get almost all of their early nutrients from the seed itself! They don’t need to draw any nutrients from the soil until later on in life.

Soilless mixes like coconut coir or peat moss can be a good option if you want to be 100% sure that there are no contaminants or pathogens in your seed starting mix. Unless your mix has been sterilized, you can’t be totally sure that it is free of pathogens.

Should You Get Sterilized Seed Mix?

When buying seed starting mix, you’ll often see the word “sterilized” on the package. This means that the manufacturer of the mix has heated the soil past the point of survival for many bacteria and harmful pathogens.

While it’s not necessary to get a sterilized mix, it’s highly recommended. Mold and fungal issues can destroy delicate seedlings. This is an especially sensitive issue if you’re growing microgreens, which are only grown to the seedling stage.

How is Potting Mix Different From Seed Starting Mix?

You’ve probably heard of potting mix before — it’s a staple for flowers, veggies, raised beds…basically any type of gardening.

But is it good for starting seeds?

In general, not really. Here are the general characteristics of potting soil:

  • It’s coarser than seed starting mix and composed of larger particles
  • It’s often too rich in nutrients
  • It doesn’t drain as well as a seed starting mix

Here are the general characteristics of a good seed starting mix:

  • It’s much more lightweight than potting mix
  • It’s composed of finer particles, making it easy for roots to navigate
  • It doesn’t contain any fertilizer

You might think that not containing any fertilizer would be a point against seed starting mix, but seeds contain most of the nutrition they’ll need for the first few days of growth.

Once your seedlings get to the point of growing their first set of true leaves, all you need to do is transplant them into a potting mix with more nutrients in it and they should thrive.

Choosing A Seed Starting Mix

Now that you know why seed starting mix is used instead of other types of soil, let’s get into what makes a seedling mix perfect for your plants.

Lightweight and Retains Water

The best seedling mixes are lightweight but still retain water well. They’ll include either vermiculite or perlite for aeration, and either sphagnum peat moss or coconut coir for water retention.

Sphagnum Peat Moss vs. Coconut Coir

Almost every seed starting mix will have either peat moss or coco coir as their base ingredient. They both provide the water retention that young seedlings need, and don’t have too many differences when it comes to that property. But there are other factors you may want to consider.

Peat moss has come under fire for being less sustainable than other options like coco coir due to the fact that it is mined from bogs and is thus non-renewable. The management of these bogs is pretty good though, almost to the point of peat moss being classified as a renewable resource these days.

Learn more: What is Peat Moss?

Coconut coir is growing in popularity as both a base for seed starting mixes and in hydroponic use due to how similar it is to peat moss. It can retain over eight times its weight in water, making it fantastic in seedling mix. Better yet, it comes in dehydrated and compressed bricks, making it easy to ship!

Learn more: Coconut Coir Explained

Perlite vs. Vermiculite

Both perlite and vermiculite add aeration to your seedling mix, making them essential ingredients for young seedlings struggling to establish themselves.

Perlite looks like tiny white puffy balls. It’s a natural material that is extremely lightweight, making it great in seedling mixes, but only in small amounts. If you use too much, it’ll just blow away!

Vermiculite is also a naturally-occurring material but has a flaky and reflective appearance. It provides less aeration than perlite, but more water retention, making it a good choice if you have less water retention in your base of coconut coir or peat moss.

Learn more: Perlite vs. Vermiculite: What’s The Difference?

Diatomaceous Earth

Diatomaceous Earth is sometimes added to seedling mix. If you’ve never heard of it before, don’t worry — I hadn’t either when I started gardening. It’s a mineral that is made up of fossilized plants called diatoms. It has the unique property of destroying almost all insects that could bug your little seedlings, which is why it’s added to seed starting mixes.

While seed mixes are usually sterilized by the manufacturer, it’s a good idea to add a bit of diatomaceous earth to the mix just to give your seedlings a better chance at survival.

Organic vs. Conventional Seed Mix

The debate around organic vs. conventional produce is still raging, but does it apply to seedling mixes as well? Make no mistake, manufacturers of seedling mixes are responding to the increased demand for organic and putting all sorts of organic seedling mixes on the market.

When it comes to seedling mix, my personal opinion is that it doesn’t matter much if you choose organic vs. conventional. Think about it – you’ve got peat moss, coco coir, perlite, and vermiculite making up the majority of the ingredients. Most of these are naturally-occurring materials that by definition are “organic” because they’re minerals. They can’t be produced in a more organic manner than they already are!

If you decide to buy an organic mix, make sure it’s certified organic.

Correct pH Levels

Because all of the ingredients in seed starting mixes have different pH levels, manufacturers often add lime to adjust the pH of the overall mix to a level that is perfect for young seedlings.

In general, your seedlings will do well with an acidic pH level between 5.5-6.5. Keep in mind that adding anything to your seedling mix will affect the pH of the entire mixture, so be careful what you add!

The Best Seed Starting Mixes

Best Organic Seed Starting Mix

Sale Espoma SS16 16-Quart Organic Seed Starter Premium Potting Mix

  • Espoma Ss16 16-Quart Organic Seed Starter Premium…
  • Premium Potting Mix
  • Country Of Origin: United States

Espoma makes a fantastic seedling mix that is around 80% peat moss. The rest of it is made up of humus, perlite, earthworm castings, and lime.

On top of that, they add in ‘Mycotone’, which is a combination of many different beneficial mycorrhizae, which help promote root growth.

This is my go-to seed starting mix if I’m growing in soil and not making my own mix.

Check Current Price

Best Soilless Seed Starting Mix

Sale General Hydroponics Rapid Rooter Replacement Plugs 50 count

  • Rapid rooter plugs are fortified with general…
  • The optimal air-to-water ratio within the plug…
  • Use rapid rooter for robust early rooting that…

I know that this recommendation is kind of cheating, but if you want a soilless seed starting mix, Rapid Rooters are honestly the best choice. I use these all of the time, especially if I’m starting seeds for hydroponics.

However, you can also use these if planting in soil and they make for extremely easy transplanting. All you have to do is just pick them up and plop them in a pot or in the ground. There’s no need to carefully hold the soil together as you transplant.

Check Current Price

Other Good Options

If neither of these options strikes your fancy, here are a few other seed starting mixes that I have personally used and recommended:

Black Gold Seedling Mix, 16qt – If you want a more luxurious option, jam-packed with beneficial mycorrhizae and well-balanced

Hoffman Seed Starting Soil, 10qt – A finer consistency and well-blended mixture that absorbs water better than most mixes

Jiffy Organic Starter Mix, 16qt – a classic organic option from one of the biggest gardening suppliers out there.

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Why splurge money when you can make your own seed mix easily? Check out these 5 Best Homemade Seed Starting Mix Recipes below.

There are seed starting mix recipes with peat or with coconut coir. One suggests to sterilize the soil for 30 minutes at 120 ° C in the oven, another at 180 ° C and a third option is to put soil in 800 watts for 10 minutes in the microwave.

In any case, there are a three basic fundamental things to note for before moving further:

Seed starting mix must be sterilized. It must be low in nutrients and its texture must be light and permeable.

Ingredients for Homemade Seed Starting Mix Recipes

The main ingredients of our seed starting mix are mostly peat moss or coco peat and vermiculite or perlite.

1. Peat moss or Coco Peat

Peat Moss

Peat improves aeration and can save a lot of water. It is acidic and contains less or no nutrients and if you’re using peat, *add 1/4 tablespoon lime per gallon in the mix to balance the pH.

The biggest downside of using peat is it can only be obtained by destroying the remaining Mires. There are peat-free alternatives like coco peat you must opt for.

Coco peat

Best and better alternative of peat moss is coco peat. Coconut fibers are offered in lightweight blocks that swell to become large when water is added. The Benefit of using coco peat over peat moss is that its production doesn’t harm the environment. It also has macro-nutrients and potassium and it is neutral, unlike peat, which is acidic.

Alternatives

Leaf Mold

Leaf mold is a kind of a lazy man’s compost. It is an outcome of the natural rotting process of leaves. You can use leaf mold to sow seeds. Here’s an interesting on The Guardian for you to read.

Pine Bark humus

Bark humus produced from the composting of the bark. The bark originates mostly from conifers. These crusts must be composted for a long period of time. The result is perfect for growing plants: Water permeable and stable structure. The small roots can grow unhindered.

Composted Wood fiber

Wood fibers have similar favorable properties as coir. They are also low in nutrients. The material must, of course, do not come from treated wood waste.

Cat Litter

Cat litter is a good ingredient for plants that require very few nutrients. For example, cacti. With a nutrient-free mixture of perlite or pumice and cat litter, you give seedlings the best ground for rooting.

Important: Use non-clumping, mineral-based cat litter.

2. Perlite or Vermiculite

Perlite

Perlite is a volcanic mineral. It doesn’t absorb water or other nutrients, thus improved drainage. It also has insulating properties that help the plant roots during fluctuation in temperature. *You can also use pumice instead of perlite.

Vermiculite

Vermiculite is light, but unlike perlite, it retains water and nutrients and release that when needed. It also helps in drainage.

Sand

You can use sand if you don’t have perlite or vermiculite. Sand is always there as a part in soil. It is important for a stable soil structure and drainage. Sand does not contain any nutrients.

3. Compost

Compost is used in a few of the seed starting mix recipes given below. If you’re using compost make sure it is fine. You can also use manure instead of it.

Must Read: Potting Soil vs Seed Starting Mix

5 Homemade Seed Starting Mix Recipes

Make seed starting mix depending on the seeds you’re sowing and their nutrient requirements.

We divided these recipes into three types: Recipe 1, for high energy requirements seeds. Recipe 2 and 3, for medium and low energy requirement seeds.

  • High requirement seeds are those that require more energy to germinate. Many annual flowers and vegetables, such as potatoes, tomatoes, cabbage, sunflower and geraniums.
  • Average requirement seeds are the ones that need less energy for germination. This includes Allium, pumpkin, cucumber, snapdragons, dahlias and gloxinias.
  • Low requirement seeds are those that require less or no nutrients for germination. They are most of the herbs, lettuce, azaleas, begonias, petunias and pansies and most of the plants belong to Crassulaceae family and palm species

Two Basic Seed Starting Mix Recipe

These two basic seed starting mix recipes are easiest, most popular and perfect.

1. The easiest seed starting mix recipe is to add 1/2 part of perlite, vermiculite or sand and 1/2 part of peat moss or coco peat.

2. Mix 1/3 part coco peat or peat moss, 1/3 part compost and 1/3 part of vermiculite or perlite or sand. In such a mix sow seeds that require more energy to grow.

Recipe 1 (High Requirement)

Peat or Peat alternatives 40%
Compost 30%
Garden soil, sand and bark humus 30%

Recipe 2 (Average Requirement)

Peat moss, coco peat or wood fiber 55%
Compost 20%
Sand 15%
Bark humus 10%

Recipe 3 (Low Requirement)

Peat or Peat alternative 50%
Perlite or Perlite alternative 45%
Bark humus 5%

Sterilization

Mix the proportion well before sterilization and make it evenly moist (especially when you are using peat moss). This happens best when the soil is kept in a discarded oven (45 minutes at 150 ° C) or in a microwave oven (10 minutes at 800 watts). This will make your soil disease free.

Caveat: Dried peat moss is flammable.

Also Read: Using Coffee Grounds in the Garden

Seed starting mix can be expensive to buy, so I came up with my own recipe for homemade seed starting medium. This is the best seed starting mix, and it’s super easy to make too! In this post, I will share my recipe, and show you exactly how to make seed starter soil from scratch.

When I talk about starting seeds indoors, one of the first questions new gardeners ask me is about the best potting soil mix to use.

This is a very important question, because the type of soil you use for growing seeds indoors really does make a huge difference – and it can make or break your seed starting success!

Using the wrong type of soil for planting seeds indoors is a common mistake. Many new gardeners think that “dirt is dirt”, so they either buy cheap potting soil, or try to use garden soil to start seeds indoors. This my friend is just a recipe for disaster.

Seed Starting Mix -vs- Potting Soil

The reason you can’t use cheap potting soil or garden soil to grow seeds indoors is because those types of soils will become compact in containers.

When that happens, it’s extremely difficult (if not impossible) for seeds to germinate, and for the delicate seedling roots to grow.

Your seed starting medium should be porous so the soil stays light and fluffy, which makes it much easier for the seeds to germinate.

A porous seedling mix also allows plenty of air around the roots – which is super important for healthy seedling growth.

In fact, the best potting soil to use for starting seeds indoors shouldn’t even contain soil at all.

What’s The Best Soil For Seed Germination?

The best seed starting medium to use for growing seeds indoors is a soilless seed starting mix that is both fast draining, and also holds moisture (sounds like a funny combo, I know).

You can buy a quality seed starter mix pretty much anywhere you can buy seeds, or you can make your own DIY seed starting mix.

I love making my own homemade seed starter mix, it’s super easy and it gives me the flexibility to modify the ingredients and make it just how I like it.

Plus I can make as much or as little as I need for starting my seeds, no need to have a big bag of seed starting mix lying around if I only need enough for one seedling tray.

Getting ready to make DIY seed starting mix

How To Make Seed Starting Mix

When I came up with my own soilless seed starting mix recipe, it was mainly because I had a bunch of the necessary ingredients laying around from making other potting soil recipes… and because buying pre-made seed starting mix is expensive.

But I also wanted to make sure the ingredients were easy for you to find too, so that I could share my recipe. These are all common ingredients that can be bought wherever you find potting soil for sale at your local garden center, or ordered online any time.

DIY Seed Starting Mix Ingredients

To make your own seed starting mix, you only need three main ingredients:

  1. Coco coir or peat moss
  2. Vermiculite
  3. Perlite or pumice
  4. Garden lime (only needed if you use peat moss)

Ingredients for DIY seed starter mix

Coco Coir -vs- Peat Moss

You can use either coco coir or peat moss as the base ingredient for your DIY seed starting mix, whichever you prefer. There are a couple of cons to using peat moss rather than coco coir…

One con for using peat moss is that it’s slightly acidic, so if you choose to use peat moss, add some garden lime to the mix to balance out the acidity.

The other con to using peat moss is that it’s not as sustainable as coco coir is. Peat moss is a renewable resource, but it is very slow to renew so it’s not as environmentally friendly.

Related Post: Seed Starting Peat Pellets Vs. Soil: Which Should You Use And Why?

Starting seeds in coco coir on the other hand is very sustainable, it is the by-product of coconut processing. It’s a wonderful additive to any DIY soil mixes, and I really love the consistency of it. It’s my top choice for adding to my homemade seed starting mix!

Coir ingredient in seed starting soil mix recipe

Vermiculite

Vermiculite is a naturally occurring mineral, and is commonly found in potting soil mixes, especially soil for starting seeds. The reason vermiculite is commonly found in potting soil mixes is because it helps the soil retains water.

Seedlings won’t tolerate dried out soil, and vermiculite helps to keep the soil evenly moist so you won’t have to water as often.

Vermiculite DIY seed starting mix ingredient

Perlite

Perlite is a very lightweight soil amendment. It’s the white pieces that look like Styrofoam that you see in many commercial potting soils.

It retains very little moisture, and prevents soil compaction. In other words, perlite helps the soil drain faster, and makes the mix porous (which is ideal for germinating seeds).

You can buy perlite in many garden centers or home improvement stores in the same section as you would find the potting soil for sale.

A great alternative to perlite is pumice, just in case you have a hard time finding perlite in your local garden center.

Perlite ingredient in seed starting soil recipe

Supplies Needed:

Along with your seedling mix ingredients, you’ll need a few other supplies to help you measure and mix your everything. So grab these items before getting started…

  • Measuring container (I usually use a 1 cup measure)
  • Trowel or large mixing spoon
  • Container for mixing (I use a bucket or my table top potting tray to mix mine)
  • Seed starting trays

DIY Seed Starting Mix Recipe

8 parts (pre-moistened) coco coir or peat moss
1 part vermiculite
1 part perlite or pumice
1/4 tsp garden lime per gallon (if you use peat moss)

(a batch using a one cup measure as your “part” is enough to fill one commercial seed starting tray)

What is a “part”? – This is a question that I get asked a lot when I talk about how to make potting soil. A “part” is just a generic unit of measure for portioning your ingredients.

Use anything you want as your part, as long as you use the same thing for each “part”. For example if you use a 1 cup measure as your part, then this recipe would convert to 8 cups coir, 1 cup vermiculite, and 1 cup perlite.

Related Post: How To Make Newspaper Seed Starting Pots

Seed tray filled with homemade seed starter mix

How To Mix Your Homemade Seed Starting Soil

Making your own mix for starting seeds is easy. First, dump all the ingredients into a bucket or bowl…

Combine seedling mix ingredients

Then simply mix the ingredients with a spoon or trowel until they are well blended. Once the ingredients are blended together, you can fill your seedling trays and start planting seeds right away.

Mixing ingredients for DIY seed starting soil

That’s it. Told you it was easy to make your own seed starting mix. You could make a bunch ahead of time and store it for later use, or just mix up small batches as you need it.

I like to mix up a big batch, and then I store it in a plastic bucket in the garage so I always have seed starting mix on hand when I need it.

Related Post: How To Make Potting Soil For Indoor Plants

Storing Your Leftover DIY Seed Starter Mix

Whether you make your own seed starting mix, or choose to buy a commercial soil for starting seeds… make sure to store your leftover soil in an air tight container to avoid attracting bugs.

These air-tight seal lids work great to keep bugs out, and they fit on any standard five gallon bucket.

Store leftover seedling soil mix in sealed container

The best part about making your own soil for starting seeds is that you can experiment with different mixes. If you find that the soil is drying out too quickly, next time add more vermiculite to the mix. If it’s staying too soggy, then add more perlite to your mix.

Oh, and this mix can also be used in seedling pots when it comes time for potting up your seedlings too!

Seedlings Growing In DIY Seed Starting Mix

If you want help to learn how to start your seeds indoors and get your seedlings off to a healthy start this year, my Starting Seeds Indoors eBook is for you! It’s a quick-start guide to help you get started growing the seeds for your garden.

Looking for even more help with growing your own seeds? Then you should enroll in the Seed Starting Course. This fun, in-depth course has everything you need to know about growing any plant you want from seed!

Products I Use To Make DIY Seed Starting Mix

More Seed Starting Tips

  • Seed Starting Supplies & Equipment
  • How To Disinfect Seed Trays And Flats Before Starting Seeds Indoors
  • How To Figure Out When To Start Seeds Indoors
  • Tips For Starting Seeds Indoors
  • How To Test The Viability Of Seeds With An Easy Seed Germination Test

Share your favorite recipe for seed starting mix in the comments section below.

Winter may still hold our gardens in its icy grip, but spring is just around the corner, so now is the perfect time to start planning your garden. There are decisions to be made: what kinds of flowers will you plant and what types of veggies will you grow in your veggie patch.

We all have different types of gardens or ways of growing plants. Some people live in suburbia and have a good amount of backyard space in which to plant their flowers and veggies. City dwellers might have access to market gardens where they can have their own little veggie patch. Urban gardeners who live in an apartment with only a small balcony will grow their colorful foliage and cultivate fresh veggies in pots.

Wherever you live and however you choose to garden, a seed starting mix will give your flowers and veggies the best start to life, and ultimately reward you with your own piece of horticultural heaven.

Image Product Name Price Rating

Black Gold 1311002 Seedling Mix

$$ A

Espoma SS8 8-Quart Organic Seed Starter Mix

$$ A

Abundant Living Deluxe Gardening Gift Set

$$$$ A+

Hoffman 30103 Seed Starter Soil Mix

$$ A

Triumph Plant Coconut Coir Fiber Bricks

$ B

Our Pick for the Best Seed Starting Mix

Abundant Living Deluxe Gardening Gift Set

This handy little pack is the ideal starter kit for new and veteran gardeners. As well as the 14 different seeds, gardening book, and a bag of seeding power, there are themed coloring cards for the kids, so that you can encourage them to explore the joys of gardening.

Check the price on Amazon ›

What is a Seed Starting Mix?

A seed starting mix, which can also be called “seed starting soil,” helps a seed to germinate into a seedling and then into a full grown plant. Some people also like to purchase seedlings from their local nursery, but this is not always the best choice as the seedling may have picked up containments or other plant diseases.

By growing your plants from a seed, you can control the process from seed to plant to plate. It can be fun, especially for kids, to wait eagerly, and then be filled with delight when the first leaves begin to appear, and then the full flower blooms or the veggies start to grow.

Soil-less

A soil-less seed mix means that the mix does not contain any field or ordinary garden soil. Regular field or garden soil can contain diseases and contaminants, which can be especially harmful to vulnerable seeds and seedlings.

You might come across the word “sterilize” in relation to seed starting mix or even potting mix, which means the manufacturer has used a heating process to kill off any bacteria or fungi or mold that can restrict the growth of your seeds and plants.

Some gardeners may choose to make their own mix, but sterilization will make sure that your seed grows into a strong and healthy plant.

Potting Mix vs Seed Starting Mix

Potting mix is probably the most well-known type of gardening product for planting flowers and veggies. Potting mix is great for repotting plants, but it may not be ideal for planting seeds or seedlings as it can be too rich. Also, it has a coarser texture and does not drain very well. Good drainage is necessary for a seed to germinate and grow into a budding plant. But in its favor, the potting mix contains fertilizer, so from seed to plant, the potting mix will feed your flowers or veggies the nutrients they need.

A seed starting mix is the preferred option as opposed to potting mix for those gardeners who prefer to plant seed, not seedlings or cuttings. It is more desirable for three reasons:

  1. It has a superior germination process.
  2. The mix is usually more lightweight than potting mix.
  3. It absorbs water easily and allows for plenty of air circulation, which is very important for the seed to be able to grow and develop into a plant.

The main difference between potting mixture and seed starting mix is that seed mix usually does not contain any fertilizer. The seed provides the necessary nutrients for the budding plant, so it does not need fertilizer. Once the plant starts to sprout leaves, you can start to add a fertilizer for ongoing nutrients.

One thing to keep in mind in regards to fertilizer is that some seed /potting mixes contain just enough fertilizer, like Diatomaceous Earth, that will provide seeds with sufficient nutrients to last up to three months or until they are grown into baby plants, while other brands may not add any nutrients. Think of it this way – a seed starting mix kickstarts the seed into accelerated growth mode.

How to Choose the Best Seed Starting Mix

Lightweight and Hydrated Mix

For your seed to grow into a healthy seedling, the best seeding mix is a lightweight and well-drained soil that has a balanced mixture of organic materials like vermiculite or perlite. The soil mix should also have excellent aeration and water retention properties so that the seed’s root can push through and have room to grow.

Some companies use an organic wetting agent to provide extra hydration like a Yucca extract, which is taken from a root vegetable to help stop the soil from drying out.

Sphagnum Peat Moss

Most seed mixes contain sphagnum peat moss, which is lightweight and highly absorbent and it helps to retain moisture for your seeds. Products that use peat moss are especially beneficial for when you are gardening in dry weather or when you forget to water your plants. The downside to using peat moss is that it can be difficult to moisten.

Perlite looks a bit like Styrofoam, small white pieces of natural volcanic mineral that can also help to provide adequate aeration and water retention to the soilless mix. It also prevents the soil from compacting and helps it to drain faster. It can also be used to cover the seeds and help them to maintain a consistent moisture level as they germinate.

Vermiculite is a naturally occurring mineral, which is found in a lot of potting mixes and can be especially helpful for planting seeds. It keeps the soil nice and moist so that the seeds or seedlings do not dry out, and it can also save you from having to continually water the seeds.

Coconut Coir Fiber

Coconut coir fiber can be used as a substitute for sphagnum peat moss, and it is used for a wide range of horticultural and agricultural uses. It can absorb and hold up to 8+ times its own weight in water. Many manufacturers offer their coconut coir in bricks, so you can just break off a piece when you need it and rehydrate it in a bucket of water.

Some manufacturers use Diatomaceous Earth (DE) as their seed starting mix, which acts like a natural, non-toxic fertilizer that will kill any insects from affecting the germination of seeds or seedlings. DE is a naturally occurring siliceous sedimentary mineral that is made from tiny fossilized algae-like plants called diatoms. The diatoms are ground up to a fine powder that looks similar to talcum powder.

DE is composed of many minerals such as magnesium, silicon, calcium, sodium, iron, and other trace minerals: titanium, boron, manganese, copper, and zirconium. Diatomaceous Earth can also help to eliminate any harmful bacteria or toxins from attacking your seeds and plants.

Organic

Organic food or products are rising in popularity. Many people are going “green” and they want their food to be free from harmful chemical additives, synthetic fertilizers, and insecticides. Environmentally friendly products are an important choice as well.

Many companies are responding to this shift and making products that they claim are organic, and may of them are, but just because the product says it is “organic” does not mean it is certified organic. So read the fine print or contact the company to make sure that the product is properly rated as an organic product or it contains organic ingredients or materials.

PH Soil Levels

The pH level is the measurement of the acidity (“sourness”) versus the alkalinity (“sweetness”) of soil. If you live in an area that has low rainfall, your soil will be more alkaline. If there is a higher level of rainfall the soil ph levels are more acidic, which is due to the rain washing away minerals like calcium from the soil.

Plants grow best when the soil is slightly acidic between 5.5 to 6.5. If you live in an area that has a lot of rainfall look for a soil mix that has magnesium and calcium added to the mix, or a mix that has a ph level of 5.6 to 5.9.

Some manufacturers use Natural Dolomite Lime, which helps to reduce soil acidity and is a good source of magnesium and calcium, which are essential plant nutrients. Diatomaceous Earth (DE) powder can also put back some of the minerals that have been washed away by excessive rain, while also helping to stimulate seed germination.

Reviews of 5 Best Seed Starting Mix

1. Black Gold 1311002 Seedling Mix

You will feel like you have stuck gold when you use the Black Gold seedling mix as it provides the right foundation to promote healthy root growth for seeds and newly germinated seedlings.

Black Gold is soil-less and it is listed as a certified OMRI organic product with a mix of lightweight, non-clumping, natural forming enriched organic matter that requires less watering over the long term.

This seeding product is fast-acting and within a week you will see your seeds spring to life. The mix contains 70-80% Canadian sphagnum peat moss, and a Yucca extract, an organic wetting agent that is taken from a root vegetable to help stop the soil from drying out. All of these materials will give your seeds the aeration, moisture retention they need to grow up into strong, healthy plants.

Black Gold comes in a 16-Quart bag and can be used for germinating seeds indoors under fluorescent lights or in pots on your patio. The mix can be dusty when dry, so thoroughly moisten it before using.

What we like:

  • Ideal for seed and seedlings
  • Good value for money
  • Lightweight mix
  • 100% organic
  • Works quickly

What we don’t like:

  • Mix is very dry straight out of the bag

Check the price on Amazon ›

2. Espoma SS8 8-Quart Organic Seed Starter Mix

Whether you are planting herbs, tomatoes, or re-potting your favorite flower, this organic seed starter from Espoma will have your garden blooming. With a rich, premium blend of natural ingredients, it is specially formulated for seed cuttings, but it also works well on newly planted seeds.

The Espoma mix contains sphagnum peat moss, peat humus, perlite, and it is enhanced with My-tone, a blend of mycorrhizae, which is a form of fungus that helps to promote root growth and improves moisture retention. In no time at all your seeds will grow and become strong, healthy and vibrant plants. The mix is available in an 8-quart bag, which has a zip-lock to keep any air or moisture out.

  • Good quality
  • Organic certified
  • Perfect for flower pots and a small herb garden
  • Good germination rate
  • Absorbs water and drains well
  • Handy zip-lock bag
  • Small bag
  • Contains a lot of debris

Check the price on Amazon ›

3. Abundant Living Deluxe Gardening Gift Set

This deluxe starter kit from Abundant Living is ideal for the no mess, no fuss gardener or as a gift for your kids to encourage them to develop an interest in horticulture. The kit includes everything you need to grow your own organic veggies, which will be free from nasty chemical pesticides or genetic modifications.

As well as the included 14 varieties of Heirloom vegetable seeds, there are beautiful garden themed coloring cards for the kids, a planning booklet with handy tips and information about gardening, and a large bag of Diatomaceous earth powder.

Once the seeds are planted the kids will want to monitor the plant’s progress, so the included 24 Jiffy Peat Pots lets them keep on the plant as it develops and grows in the safety of the indoors before it is ready to be transplanted to the garden.

The kit also includes one set of latex gloves and kitchen shears. Each gift set that is purchased helps to support the Hope Center for Women, Inc.

  • Very good quality
  • All-in-one gardening starter pack
  • Beyond Organic gardening book
  • Large collection of seeds
  • Organic and Non-Hybrid, Non-GMO
  • Good size bag of Diatomaceous earth powder
  • Great gift idea
  • Expensive

Check the price on Amazon ›

4. Hoffman 30103 Seed Starter Soil Mix

Hoffman has been creating high-quality gardening products for the passionate home gardener since 1934, and the Hoffman seed starter soil mix will have your flowers and veggie patch flourishing quickly.

The soil mix contains six premium components such as Canadian sphagnum peat moss, all of which are specifically blended to promote superior germination of seeds. You can also use the soil for transplanting and encouraging root cuttings.

As you soon as you open the bag, you are greeted with a rich garden smell and the soil has a good ph level that ranges from 5.6 to 5.9. The soil also has a relatively fine consistency and it absorbs water easily and allows for plenty of air circulation, which is important for seeds to become healthy and strong plants.

The soil comes in a 10-quart pack that has a handy ziplock to keep the soil safe from any moisture or air contaminants. If you would like a complete list of the ingredients in this mix, you can contact the supplier @[email protected]

  • Ideal for seeds and cuttings
  • Very good quality
  • Premium soil mix
  • High water absorption rate
  • Allows for good air circulation
  • Good seed germination
  • Zip-lock bag
  • Some seeds are slow to germinate

Check the price on Amazon ›

5. Triumph Plant Coconut Coir Fiber Bricks

Triumph Plant is one of the most trusted brands of seed starters soil mixes. The pure coconut coir fiber comes in a brick, and as the fiber is 100% organic, biodegradable, Ph neutral, and disease resistant, with no odor, pests or weeds, it will give your vegetables and flowers their best chance to grow and flourish.

Triumph use carbon-rich coconut coir that is environmentally friendly, and is a natural and sustainable alternative to peat moss. Coconut coir is more effective at hydrating the soil and releasing life-giving nutrients and moisture to seeds and plant’s roots.

The coir fiber comes in 230-gram bricks and when you mix it with water it turns into a light fluffy mixture. It can be used for a wide range of gardening purposes: seed germination, Hydroponics, cultivating mushrooms, worm farms, and landscaping corrosion control. The bricks are easy to use, just add 50-60 ounces of warm water to each block. Wait 10 minutes. Stir. Sit back and relax and watch your seeds spring to life. You can also mix the coir in with others soils, but it works very well by itself.

The mix can be stored for long periods, but make sure the packet is well sealed to stop mildew.

  • Affordable
  • High-quality coconut coir fiber
  • 100% organic and environmentally friendly
  • Can be used with or without soil
  • Good hydration
  • Very effective
  • Versatile
  • Easy to use bricks
  • Bricks are very small
  • No zip-lock bag

Check the price on Amazon ›

Best Seed Starting Mixes: Guide & Recommendations

Updated January 30, 2019

We tested eleven different purchased seed starting/germinating mixes, as well as potting mix, garden soil, and a variety of home-made mixes. While we can’t comment on the make-up of the mixes (other than noting what the manufacturer indicates is in the package), here are our observations about the look and feel of each mix, how it reacted when moistened and placed in pots, how well it retained moisture, and how well seeds germinated and grew in it.

Although the instructions on some mixes suggest filling the seed starting container with dry mix and then watering after seeds have been planted, we highly recommend that all mixes should be thoroughly moistened with lukewarm water before use. Make sure everything is well mixed so that there are no dry areas. Don’t over-wet the mix; if water drips out when you squeeze the mix in your hand, it’s too wet.

We describe each seed germination mix below and also indicate whether or not a mix is organic (note that definitions of “organic” vary and not all organic mixes are OMRI listed; we simply report whether or not the manufacturer states that the mix is acceptable for use in certified organic production).

*** If you’re just looking for our top recommendations, scroll to the bottom of this article.

How to Successfully Start Seeds Indoors

This video tutorial shows you exactly how to successfully start seeds indoors, including seed starting mix, containers, sowing, watering, heat, and more.
>> Watch the video on our YouTube channel (28 minutes)

How to Care For Seedlings After They’ve Germinated

After seedlings emerge they need specific care in order to thrive. This video covers lighting, watering, air circulation, fertilization, thinning, transplanting and hardening off.
>> Watch the video on our YouTube channel (29 minutes)

Organic Seed Starting Mix, 6 Qts. (Gardener’s Supply)

This mix contained larger pieces of organic matter (such as twigs and bark), probably from the compost that’s included in the mix. These pieces can interfere with seed germination and growth so we recommend picking them out of the mix before you moisten it (it’s much harder to remove them when wet). It also contains sphagnum peat, rock phosphate, gypsum, protein meal, and perlite.

You’ll need to add quite a bit of water to adequately moisten this mix prior to use.

One 6 quart bag of Organic Seed Starting Mix will easily fill two 24-cell (2-inch) seed starting trays. It may fill three trays if you don’t fill each cell to the top.

Grow Kit Pellets (Gardener’s Supply)

These compressed coconut coir pellets come with Gardeners’ Supply’s new Grow Kit but can also be purchased separately and can be used in any similarly-sized growing tray.

Simply drop one into each cell in your seed starting tray and place the tray in water. The pellets swell up very quickly when water is added and will fill each cell. The moistened mix has a nice, even texture and it’s easy to work with. For seeds that need to be covered with a thin layer of soil, you may want to sprinkle a different mix over the surface after seeds have been sown.

Pro-Mix Organic Seed Starting Mix (Premier Tech Horticulture)

This organic (OMRI listed) mix comes in a 16-quart (6 lbs) bag. It contains a mixture of Canadian sphagnum peat moss (70-80% by volume), coir, perlite, a soy-based natural fertilizer, and mycorrhizae. We found that there were a lot of plant parts and roots in the mix, probably from the peat moss. Screen the mix before wetting to remove the larger pieces that could affect seed germination.

We found that this mix stayed very wet so be careful not to overwater and keep an eye on the moisture level. Wet mixes can create problems with damping off.

Wonder Soil Seed Starting Pellets

These small pellets (about the size of a very thick dime) are made of compressed coir pith, worm castings, mycorrihizae, water-saving polymers, and a small amount of plant nutrients. Because it contains mycorrhizae, it’s recommended that you use it within a year or two of purchase as the potency will decrease by about 10% each year.

Pellets can either be placed directly into cells in seed starting trays before wetting, or poured into a bowl or bucket, wetted and mixed, and then added to seed starting trays. The pellets expand very quickly when moistened and form a very fine, granular mix. Be sure that all pellets have been thoroughly wetted – if not, they’ll continue to expand in the seed tray and can push seeds right out of the tray. As with the Grow Kit pellets, you’ll probably need to use a different germination mix to cover seeds (or expand a few extra pellets to use as a seed cover).

One package of seed starting pellets will fill two 24-cell (2-inch) seed starting trays. The label says that the whole package will fill 150 cells, but those are the much smaller 1/2-inch cells.

Germinating Mix (Gardener’s Supply)

This fine, even mix contains finely-milled sphagnum peat moss, vermiculite, and some trace minerals. It’s mixed exclusively for Gardeners’ Supply and is suggested for use with their Accelerated Propagation (APS) growing systems.

It’s very lightweight and easy to work with, although it’s pretty dusty when you open the bag and it does take quite a bit of water to moisten it thoroughly. Because there aren’t any larger-sized pieces in the mix, it spreads evenly in small seed starting containers.

Eco-co Coir Seedstarting Mix (Gardener’s Supply)

Made from the husks of coconut shells that have been ground, dried, and compressed, the EcoCoir block expands a lot when water is added. Don’t be fooled by the small size and light weight of the block into thinking that you can mix it in a smaller bucket. The instructions specify a 5-gallon bucket or container – and you’ll need it!

The mix contains a lot of coconut shell fibers that make it a little more difficult to work with.

Potting Mix (Miracle Gro)

This mix is commonly used in outdoor containers but, since people often ask whether or not they should use potting soil to grow seedlings, we decided to see how well it would work.

This mix includes compost (made from “forest products”), sphagnum peat moss, perlite, a wetting agent, and enough fertilizer to feed plants for up to six months. It’s lightweight but does contain many pieces of organic matter (small pieces of twigs, bark, and roots) that make it more difficult to work with in seedling trays. It also doesn’t absorb water readily when it’s dry to be sure to moisten it well before use.

Garden Soil

Garden soil is generally not recommended for seed starting; it tends to contain weed seeds and pathogens that can kill seedlings and it usually of a poor consistency for staying moist but not wet. Still, people often wonder whether garden soil would work for starting seeds so we decided to test it.

We used a humus-rich sandy loam from a healthy, organic vegetable garden. Lettuce, carrots, beans, peas, and squash had previously been successfully grown from seed in this garden soil (outside).

Bar Harbor Blend Premium Potting Soil (Coast of Maine)

This potting soil is made with a mixture of lobster compost, cow manure compost, kelp, peat, and perlite. While it’s not marketed specifically for seed starting, we thought it was worth trying.

The Bar Harbor Blend is lightweight and easy to use. We found that the mix stayed fairly moist (probably because of the high compost content) so be careful not to overwater.

Black Gold Seedling Mix (Sun Gro)

The Black Gold mix is appropriate for organic seed germination (it’s OMRI listed). It contains about 70-80% Canadian sphagnum peat moss, perlite, dolomite lime, and yucca extract (which acts as a wetting agent) and comes in a 4 lb bag.

The mix is extremely lightweight and dusty when dry. Be sure to thoroughly moisten it before use because it doesn’t easily absorb water if it’s placed into a seed starting tray when it’s dry.

CocoTek and Earthworm Castings

CocoTek is a compressed natural coconut coir block that’s sold for use in hydroponic cultivation. Because it contains no nutrients, we paired it with organic earthworm castings with an NPK rating of 1-0-0.

One 1.4-lb block of CocoTek absorbs up to 1.5 gallons of water and expands to five times its size so be sure to mix it in a large container. You can mix it with a variety of other growing media, such as perlite, compost, or peat to customize the nutrient and water holding capacity of the mixture.

Our Testing Process

We tested a range of seed starting kits/containers (review coming soon) and lights (review coming soon). All containers were either new or had been sterilized prior to use.

Half of the seeds were started on a heat mat, the others were started at room temperature. Heat was removed when most seeds in a tray had germinated.

All of the seed starting mixes were kept moist using a capillary mat that was watered from beneath; each mix absorbed as much water as it “needed” with no supplemental watering.

Once seeds germinated, they were kept under grow lights for 16 hours per day.

No fertilizer was applied to seedlings. Normally, we would add fertilizer to encourage healthy growth. In this case we chose not to so that we could evaluate the capacity of the seed starting mix to support seedling growth.

All seeds were zinnias that were kindly provided by Renee’s Garden Seeds (we also used tomato, sunflower, and zucchini seeds in other experiments).

Testing Results

As they say, a picture is worth a thousand words. So here are the results of our tests…

Each row (front to back) was filled with the same mix. There are two trays of each kind (reviews coming soon), each one grown under a different set of lights (reviews coming soon). These photos were taken 6 weeks after planting the seeds.

From left to right, the trays below are filled with:

  • Organic Seed Starting Mix from Gardeners’ Supply
  • Grow Kit Pellets from Gardeners’ Supply
  • Pro-Mix from Sun Gro
  • Wonder Soil Seed Starting Pellets
  • Germinating Mix from Gardeners’ Supply
  • Eco-co from Gardeners’ Supply

In the trays below (photos taken 4 weeks after planting), from left to right, you’ll see:

  • Garden soil
  • Coco-tek with worm castings
  • Bar Harbor Blend Premium Potting Soil from Coast of Maine
  • Black Gold Seedling Mix from Sun Gro
  • Potting Mix from Miracle Gro
  • Eco-co from Gardeners’ Supply

Highly Recommended Seed Starting Mixes

Based on everything we saw during our seed starting trials, here are the germinating mixes that we most highly recommend. We believe that these will give you the best chance of germinating and growing strong, healthy plants.

Coast of Maine Sprout Island Organic Seed Starter – Although this mix wasn’t part of the original testing back in 2014 (it wasn’t available then), I’ve since tested it extensively for germinating and growing a wide range of seedlings, from tomatoes and peppers to vines, perennials and herbs. It’s an excellent mix that stays moist without getting soggy (so requires less frequent watering), holds together when removing seedlings from seed starting trays or pots, and has had nearly 100% germination rates with all seeds I’ve tried. It’s the one mix I now use for all my seed starting.

Organic Seed Starting Mix from Gardeners’ Supply – This mix produced the largest, strongest, and stockiest plants. They appeared to be the most healthy of all seedlings and had one of the highest germination rates (66.7%). The mix stayed moist but not wet.

Germinating Mix from Gardener’s Supply – With an 83% germination rate, this mix produced the most seedlings. However, we found that the seedlings germinated using a heat mat tended to be smaller in this mix and one seedling tray developed a green slime on the soil surface. We recommend using this mix without supplemental heat.

Recommended Seed Starting Mixes

While these mixes seemed to perform quite well, they required a bit more maintenance (e.g., supplemental feeding, careful watering, use of a specific growing tray) to produce healthy seedlings.

Grow Kit Pellets from Gardeners’ Supply – These pellets performed differently in different seed starting trays. In the Grow Kit (also from Gardeners’s Supply), 100% of seeds germinated and grew well. In other seed trays, germination results ranged from 12% to 62% and the plants tended to be smaller and somewhat chlorotic (likely due to the lack of nutrients in the coconut coir; supplemental fertilizer is clearly needed). We recommend the pellets for use in the Grow Kit but would choose other mixes in non-Grow Kit seed trays.

Black Gold Seedling Mix from Sun Gro – Only half of the seeds sown in this mix germinated but they grew strongly. The mix stayed nicely moist without being too wet.

Potting Mix from Miracle Gro – Although not normally recommended for seed germination, the potting mix worked out quite well, with 75% of seeds germinating. Once moistened, it tended to stay fairly wet so be careful not to overwater. Because of the fertilizer integrated into the mix, there’s no need for supplemental feeding.

Not Recommended Seed Starting Mixes

In our tests, these mixes failed to produce strong, healthy seedlings, had low germination rates, or undesirable growth, such as fungus or green slime. Under different conditions (e.g., manual watering, rather than using a capillary mat) they may perform better. However, we felt that under the conditions that many home gardeners have, these mixes would not be a good choice.

Garden soil – Well, the advice to not use garden soil for seed germination turned out to be correct. Only one seed germinated, although it looked pretty sickly. On the other hand, the weed grew quite well, as did the green slime. The soil looked like mud after being watered; it looked much, much better in the garden – and that’s where we recommend you leave it!

Bar Harbor Blend Premium Potting Soil from Coast of Maine – Few seeds germinated in this mix, perhaps because it stayed very wet. The 25% of seedlings that survived did quite well, probably because of the nutrients provided by the compost in the mix. We don’t recommend germinating seeds in this mix but it would work quite well for growing seedlings on before transplanting outside.

The Eco-co mix grew a fungus.

Eco-co from Gardeners’ Supply – This mix stayed consistently moist (but not wet) and most seeds germinated (75%). However, the seedlings were small and spindly; we recommend starting a regular fertilization regimen within a week of germination. We also found that one seedling tray developed a fungus growth of some sort in all of the Eco-co cells.

Green slime covered most of the Pro-Mix surface.

Pro-Mix from Premier Tech Horticulture – Although all of the seeds initially germinated, they quickly wilted and most died. Those that survived were very small and weak. The mix stayed very wet and grew a green slime over the entire surface.

CocoTek and Earthworm Castings – The mix stayed very, very wet and developed a thick layer of green slime on top. It may have worked better without the earthworm castings.

Wonder Soil Seed Starting Pellets – With an overall germination rate of only 50%, this mix was one of the worst performers. Although the mix stayed nicely moist, seedlings were weak and stunted and green slime appeared in many cells.

Where to Buy

Many of these seed germinating mixes can be bought in your local big box store or garden center. Those from Gardeners’ Supply can be purchased on the Gardeners’ Supply website. Or, as with most things these days, you can buy from Amazon through the links below.

  • Organic Seed Starting Mix, 6 Qts. from Gardener’s Supply
  • Grow Kit Pellets from Gardeners’ Supply
  • Black Gold Seedling Mix from Sun Gro
  • Potting Mix from Miracle Gro
  • Coast of Maine Sprout Island Organic Seed Starter

Related Reviews and Resources

  • How to Successfully Start Seeds Indoors – Video and article
  • How to Care for Seedlings After Germination – Video and article
  • Five Keys to Successful Seed Starting
  • Growing Seedlings Indoors Under Grow Lights – Everything you need to know to do it right
  • When to Start Seeds Indoors – Perennials, herbs and some veggies are best started early indoors
  • Where to Buy Seeds – Online sources for high-quality seeds

Which seed starting mixes have you used or made? What worked best for you? Let us know in the comments below!

Last update on 2020-02-01 / Affiliate links / Images from Amazon Product Advertising API

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Potting soils and seed-starting mixes for your garden

March is the month when smart gardeners gear-up for the growing season by starting vegetable and flowering seedlings. One important factor that will determine the degree of success is the potting media.

All seed-starting mixes and potting soils are not created equally. As you visit area garden centers you will see products such as Miracle Grow, Scott’s, Farfard, Schultz, Happy Frog, Hyponex and others. Experienced gardeners generally have their favorites, while beginners may be at a loss as to what potting media to select.

According to Michigan State University Extension, there is a difference between potting soil and seed-starting mix. Soilless seed-starting mixes have a finer texture and are made from ingredients such as milled peat moss, perlite, coconut coir fiber and vermiculite. Although potting soils may be used to start seeds, they tend to have a more coarse texture and may contain field soil, compost or composted manure along with vermiculite, peat moss or perlite. Some seed-starting or potting mixes may contain fertilizer as an additive. Read the package. Some products contain enough fertilizer to provide seedlings with sufficient nutrients to last up to three months, while others may have no added nutrients.

Although most soil mixes contain some peat moss which absorbs and helps retain moisture, some manufacturers add moisture retention granules to their soil mixes that expand many times their size as they absorb water. These are especially beneficial for container gardening during dry weather or when you forget to water your plants. When potting soil ingredients include field soil, compost or manure, they may also contain some weed seeds. Although this may be an inconvenience, few seeds will be viable if the soil has been pasteurized.

Organic gardeners prefer to use organic potting media, but be aware that the term “organic” on the package does not mean that the mix would be acceptable for starting organic seedlings. Read the package closely to determine if the soil and other additives are approved for organic production.

For smart gardeners hoping to save a little money, making your own seed-starting or potting mix is an option. I like to mix one-third part spaghnum peat moss or coconut coir fiber with one-third part finely screened compost and one-third part vermiculite. Add about 1 to 2 cups of worm compost to a 5 gallon bucket of your soil mix. I also like to stretch commercial potting media by adding up to 50 percent screened compost. I generally use this mixture when transplanting seedlings into larger pots.

When I purchase commercial potting media, I like to select those that have a guarantee. To me, a guarantee indicates that a company is willing to stand behind their product. Keep the sales receipt just in case you are not satisfied with the performance of the product. It is generally required to obtain a refund.

Visit my online class for more additional information on growing seedlings (high speed internet connection is required).

For more information on a wide variety of smart gardening articles, or to find out about smart gardening classes and events, visit www.migarden.msu.edu.

Choosing the Right Soilless Mix

The term potting soil has become something of a misnomer in today’s world of container gardening. Most bags of potting soil contain no field soil but are composed of a variety of organic and inorganic materials and are referred to as soilless mixes. As a commercial greenhouse operator and horticultural researcher, I’ve worked with all kinds of soilless mixes over the years and believe them to be far superior to soil-based mixes for a variety of reasons. Many excellent brands are readily available at chain stores and garden centers. If you have a clear understanding of the requirements for a good container medium and the various ingredients used in these products, choosing the right mix for your container plantings is in the bag.

Successful container gardening requires a potting medium that meets several of the plant’s needs. The medium must be a stable reservoir of moisture and nutrients and remain loose enough to allow for root and water movement and the exchange of gases in the root zone. A growing medium must also have a pH (a measure of the alkalinity or acidity of a medium) that can support adequate nutrient uptake, and it must be free of soil-borne diseases, weed seeds, and toxins. Finally, a container medium must provide adequate anchorage and support for the roots while still being heavy enough to provide sufficient ballast to prevent plants from tipping over. A well-blended soilless medium can easily satisfy all these requirements and do so without the inherent problems and variability frequently encountered when field, or native, soils are used in containers.

If you have a good mix, water will penetrate it quickly and drain freely from the bottom of the pot. When the excess water has drained away, air will fill the large pore spaces, but enough water will be retained in the smaller spaces to provide ample moisture for the plant. In a poor mix, water may be slow to penetrate, the medium will become heavy and waterlogged, and a crust from algae or accumulated salts may form on the surface. Under these conditions, the roots become starved for oxygen, plant growth slows, foliage may begin to yellow, and plants often succumb to root rot.

For the best results:

• Lightly moisten the mix before filling containers.
• Don’t pack the mix too tightly when planting.
• Water your pots thoroughly after planting.
• Begin fertilizing your pots two to three weeks after planting if you did not include a slow-release fertilizer at planting time.

Both organic and inorganic ingredients serve a purpose

Peat mossComposted pine barkCoir

Organic ingredients hold water and nutrients
Some organic ingredients, such as peat moss, provide needed water-holding capacity, and others, like pine bark, can lend a porous structure to avoid compaction.

Peat moss: The physical and chemical properties of peat moss make it an ideal base for most soilless mixes because it can hold both water and air. It’s light, but its fibrous structure allows it to hold 15 to 20 times its weight in water. The peat fibers also give it a large amount of pore space (80 to 90 percent of its total volume). It holds nutrients well, and it readily shares them with the roots, thanks to its slightly acidic pH. Horticultural-grade peats come from the decomposed remains of sphagnum moss species that have accumulated over centuries in peat bogs. They are not a renewable resource, however, and concerns about the sustainability of harvesting this product is a common topic of discussion among gardeners. Another type of peat that is used in soilless mixes is known as reed-sedge peat, but this material is generally inferior to sphagnum peat.

Composted pine bark: This material is a renewable resource and is one of the most widely used components in commercial container media, although barks from many other species are also processed for this purpose. Bark lacks the moisture-holding capacity of peat moss, but it can dramatically increase the porosity of a mix. Bark particles used in container media generally range in size from dustlike to about 3/8 inch in diameter.

Coir: Another renewable organic material is coir, a derivative of coconut hulls that shows promise as a peat substitute. Coir has exceptional water-holding capacity, and when mixed with pine bark, it can eliminate or substantially reduce the need for peat moss in a mix. Other sources of organic matter that can be used in soilless mixes include composted manures, leaf mold, and crop residues such as rice hulls.

Inorganic ingredients improve drainage and add weight

Inorganic ingredients improve drainage and add weight Inorganic ingredients like sand, vermiculite, and perlite generally lend porosity to a mix, but they can also help retain moisture and add weight or density.

Sand: This material can add needed weightto peat- and bark-based mixes and fill large pore spaces without impairing drainage. Coarse sand is preferred in most cases, and sand ground from granite is used in the best mixes. Fine sand with rounded grains like that found at the beach can actually reduce drainage when used in excessive amounts.

Vermiculite: A mineral that has been heated until it expands into small accordion-shaped particles, vermiculite holds large amounts of both air and water. But it can easily be compacted, so avoid packing down mixes containing large quantities of it. Vermiculite can also retain nutrients and help a mix resist changes in pH.

Perlite: One of the more common ingredients in commercial potting mixes, perlite is an inert ingredient manufactured by heating a volcanic material to produce lightweight white particles. It promotes good drainage while holding nearly as much water as vermiculite. Other inorganic materials that are useful in potting media include polystyrene (plastic) beads and calcined clay, which is similar to kitty litter. Plastic beads are inert and serve only to promote drainage, but calcined-clay particles can actually improve the moisture- and nutrient-holding capacity of a mix.

The ideal mix: Generally, most container plants will thrive in a mix that contains about 40 percent peat moss, 20 percent pine bark, 20 percent vermiculite, and 20 percent perlite or sand.

SandVermiculitePerlite

Soilless mixes leave the fertilizing to you

Soilless mixes have little natural fertility, so they need fertilizer, lime, and sometimes other materials added to them to give the plants nutrients. Many soilless mixes contain a “starter charge” of fertilizer that can satisfy the nutritional requirements of plants for a few weeks, but longer-term fertility maintenance can require the addition of liquid fertilizers on a regular basis. Another option is the application of a slow-release fertilizer, which provides a constant supply of available nutrients and can either be incorporated into the medium or simply top-dressed on the surface. The rate of nutrient release for most of these fertilizers is regulated by temperature, so plants receive more fertilizer when they are actively growing, and frequent watering will not leach the nutrients from the mix. Slow-release fertilizers are available in various formulations that can provide adequate nutrition for as short as three months or as long as two years.

Soilless mixes also have limited reserves of trace elements, so for best results, choose a fertilizer that also contains these micronutrients. Some mixes now come with slow-release fertilizers incorporated into the medium, and in these cases, the fertilizer analysis is usually included on the bag’s label.

Most commercial mixes have ample lime added, so the pH should remain fairly stable over time. Soilless media perform well at a slightly acidic pH, so the lime requirements for these mixes are not as critical as for native garden soils. When in doubt about the fertility of a soilless mix, a soil test may be useful, but be sure to indicate that you have an artificial or greenhouse medium when submitting your samples.

One positive trend in soilless media products is improved labeling on the bags. Many products now list all the ingredients and additives on the package (mixes with systemic insecticides added are always clearly labeled). If you have an understanding of what components do in a mix, then choosing the right product for your container gardening needs has never been easier.

Why don’t native soils belong in pots?

Photo/Illustration: Jennifer Benner

Field soils can be appropriate for growing plants in the garden, but these soils are unsuited for growing plants in containers. In most cases, the texture of field soils is simply too fine to ensure adequate aeration in containers, and pots or planters of any size are generally too shallow to permit proper drainage. Soilless media have larger particles, which form bigger spaces or pores to hold air in the medium, while still retaining enough water for plants to survive. Adding too much water-absorbing material, which expands greatly when moistened, can knock your plants out of their container.

Photo/Illustration: Scott Phillips Adding too much water-absorbing material, which expands greatly when moistened, can knock your plants out of their containers.

Use crystal polymers to help retain moisture
Many soilless mixes have either liquid surfactants or gel-forming granules added to help them retain moisture. If you have trouble keeping containers well watered in hot weather or in sunny locations, you may want to consider adding one of these products to your mix before you plant. As with fertilizers, follow the label directions and don’t overapply. Soilless mixes that already have extra wetting agents typically indicate this on the label.

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