If you’re like me, you’ve probably been in this position before…
You’re standing in the garden center trying to decide between perlite and vermiculite. All you can remember is that one looks like little Styrofoam balls.
The difference between perlite vs vermiculite is important to know for the prosperity of your garden. They seem very similar, but differ in a few crucial ways.
Let’s get into the details and clear up any confusion you have!
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- What is Perlite?
- What is Vermiculite?
- More Differences Between Vermiculite and Perlite
- Which To Use In Your Garden?
- What is Perlite good for? Uses, types, and comparing growing media
- How perlite is made?
- Uses for perlite
- Types of perlite
- Pros and cons for gardening use
- Growing herbs in perlite
- Perlite vs other components
- Perlite; a great way to improve drainage (And a primer on what ‘organic’ means)
- What Is Perlite Made Of: When and how to use it
- What is perlite
- What is perlite made of
- How to use perlite in your garden
- Where to use perlite
- Perlite in hydroponics
- What types of perlite are there?
- Where can I buy perlite?
- Perlite in the Garden: To Use or Not to Use?
- Characteristics of Perlite
- When is it Best to Use Perlite in the Garden?
- Additional Tips for Using Perlite in Your Grow Medium
- What Is Perlite: Learn About Perlite Potting Soil
- Perlite Soil Info
- Uses of Perlite
- When to Add Perlite Soil to Container Gardens
- Dreaming of a beautiful, productive veggie garden?
- What is the Difference Between Perlite Soil and Vermiculite Soil?
- What Should be in Container Garden Soil?
- Compost for Container Garden Planting Mix
- Using Peat Moss and Sphagnum Moss in Container Garden Potting Mix
- Should you Add Mulch or Wood Chips to Container Gardens?
- Water Needs of Container Gardens
- Purchasing the Right Potting Mix for Container Gardens
- Related posts:
What is Perlite?
Perlite is lightweight, easy to handle, clean and has no odor. It has a pH of 6.6 to 7.5.
The life of a bag of perlite begins as volcanic glass — but not any type of volcanic glass. It’s formed when obsidian contacts water, creating a unique type of volcanic glass with a high water content. When manufacturers apply heat to perlite, it puffs up into little white balls. Often times they’ll mix these little white balls — what we call perlite — into potting soils to aid with soil aeration and water retention. It retains some water but also air on the surface of the little balls in all the hidden nooks and crannies.
Perlite is a good choice when you have plants in your garden that require soil to dry out completely between watering. For example, if you’re growing a cactus or a succulent, perlite is a great addition to the soil.
Because it’s so porous, perlite does allow excess water to drain quickly…sometimes all over your porch. It has a tendency to easily crush into a powder between your fingers, but this usually isn’t a problem because it doesn’t encounter that type of pressure in your pots or beds. It’s chief use is to improve soil aeration, lightening the soil and giving better drainage and oxygen access for your plants’ roots.
What is Vermiculite?
Vermiculite interacts with potassium, calcium and magnesium in your soil. It also helps to raise the pH slightly of your plants even though it’s a neutral pH of 7.0.
Vermiculite is made from compressed dry flakes of a silicate material which is absorptive and spongy. The color of vermiculite is a golden brown to a dark brown and is a sometimes difficult to tell from the potting soil it’s mixed with. When water is added to vermiculite, the flakes expand into a worm-like shape and act like an absorbing sponge. If you want to poke these “vermiculite worms” with your fingers, you’re not alone — that’s what I wanted to do when I first saw them too!
Vermiculite is best used for plants that require soil to stay damp and not dry out. For plants that love water, using vermiculite or mixing a healthy scoop of it into your potting soil is the way to go. It can absorb 3 to 4 times its volume when water is added, making your pots a little bit on the heavy side.
Since vermiculite acts like a sponge and absorbs more water than perlite, it doesn’t aerate the soil as well. This means less oxygen for plant roots. If you use it when growing plants that don’t need damp soil, you might find your plants suffering from root rot. So be aware of your plants’ needs when you decide how water retentive you want your soil to be.
More Differences Between Vermiculite and Perlite
There are major differences between vermiculite and perlite, making it important to choose the right one, lest your garden be ruined by a bad growing media choice.
We’ve already covered the biggest difference: Vermiculite will mix with soil and help to retain water. Perlite, on the other hand, will add drainage to the soil that it’s mixed with.
Vermiculite finds its way into many seed starting systems. It both protects seedlings from fungus that so often ruins seed starting, and helps to retain water in the tiny little pods that seeds start in. While perlite can be used with seedlings, it’s better used when you move your seedlings into separate pots for additional drainage.
Which To Use In Your Garden?
There’s a large discussion in the gardening community on which to use in the garden. Here’s the truth: it’s a false debate. They both have their own purposes in the garden.
Use Perlite If…
- You have plants that need to dry out before watering again
- When you move your seedlings to separate pots
- You need to loosen clay soil in your garden
Perlite when added to clay soils, it can eliminate both surface crusting and puddles. It will also help to reduce fluctuations in soil temperatures in your garden soil. Perlite will also improve both drainage and aeration in your home gardens. Horticultural perlite can be bought in different grades according to how you’re going to use it. For general application, a fine to medium grade can be used. It’s free of weeds, disease free and sterile.
Use Vermiculite If…
- You need an additive for plants that need to be kept moist
- You want your seed trays to develop strong seedlings
Vermiculite is odorless, can be purchased in horticultural-grade bags with directions on working it into the garden soil. It’s a permanent soil conditioner and won’t break down in your soil like compost does. When it is watered or it rains, the vermiculite will hold water in the soil until the soil begins to dry out and releases it. Vermiculite can be used in potted containers, on lawns and for composting. It can be used in mycology for mushrooms added to the substrate. It can improve the soil that needs an additive to retain water for your plants which need it.
In summary: Both are good additives to your gardening needs, you just need to know what you’re using them for!
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What is Perlite good for? Uses, types, and comparing growing media
Ever take a look at the potting soil in your container plants and think those little white specks are styrofoam? If so, you’re not alone. Although extremely similar in appearance (and “clinginess”) to styrofoam, those little white balls in your potting mix really aren’t styrofoam after all. They are actually little bits of expanded rock called perlite and have a very valuable place in gardening and horticulture.
How perlite is made?
A natural volcanic glass, perlite is typically made from the hydration of obsidian. The chemical made up is seventy to seventy-five percent silica or silicon dioxide; the remaining twenty to twenty-five percent is a mix of aluminum oxide (Al2O3), oxides of sodium, potassium, iron, magnesium, and calcium, and moisture (1).
To create the perlite we are familiar with, the gray to black obsidian rock is mined, crushed into smaller fragments, and then heated to very high temperatures. Once temperatures reach 850-900 ℃ the perlite becomes soft. Water trapped inside the rock vaporizes and tries to escape, expanding the rock to more than 10 times its original volume and changing the color or perlite to white. An extremely similar process to making popcorn.
The resulting expanded perlite is a lightweight material full of tiny little air pockets; it is clean, sterile, and resists compaction. The pockets on the outside absorb water, blocking moisture from entering into the center of the perlite pieces.
Close up of crushed perlite.
Uses for perlite
Yes, most of us are familiar with perlite because of its uses in gardening, but it actually plays important roles in other industries because of its lightweight nature and other advantageous properties.
- Gardening: Perlite can be added to soilless mixes to improve drainage and aeration, providing more oxygen to plant roots. It is also added to gardens as a soil additive to improve soil structure. Perlite also helps reduce soil compaction in clay soils. It is used as a standalone product to germinate seeds, root cuttings, and anchor/support root systems in hydroponic gardening setups. Epsoma is a great option for perlite and other gardening needs. Purchase it on Amazon here.
- Construction: Perlite is used as loose fill material in hollow concrete blocks or masonry walls for insulation.
- Filtration: Perlite is increasingly being used to filter solids out of liquids in many applications. It is used to filter beer before it’s bottled to remove sediment and is used to filter stormwater runoff from roads and highways.
- Manufacturing: Perlite is also used as an ingredient in lightweight concrete and plasters, ceiling tiles, and acoustical sprays to name a few.
Types of perlite
After heating and expansion, horticultural perlite is separated into four different grades based upon the particle size: super coarse, coarse, medium, and fine grade.
- Super coarse perlite has particles ranging in size between ¼ and 3/32” with a water holding capacity of 19%. Creates the best porosity for drainage and aeration but isn’t as popular in gardening because of the particle size.
- Coarse perlite ranges in size between 3/16 and 3/64”, with a 34% water holding capacity. Considered an all-purpose grade it is a good balance of drainage and water holding capacity. Due to its size, it doesn’t blend well with garden soil but makes a great media for succulents and orchids.
- Medium grade perlite is a middle ground between the coarse and fine grades ranging in size between ⅛” and 1/32”. It has a 46% water holding capacity and is best to use alone as growing media for potted plants and potted seedlings or as an ingredient in potting mixes with other components.
- Fine grade perlite has the smallest particle size, with pieces between 1/16 and 1/128”. With a water holding capacity of 52%, it works well for rooting cuttings and starting seeds.
Pros and cons for gardening use
As with so many other products, perlite has both its advantages and disadvantages as a growing media. In this case, the advantages far outweigh the downfalls boosting its popularity in the horticulture industry.
- Its sterile nature makes it highly suitable for starting seeds. There is little risk of root rot or damping off (2).
- Naturally contains minerals needed for plant growth.
- A non-toxic substance that doesn’t require rinsing like some other growing media does prior to use.
- Neutral pH doesn’t need to be adjusted, nor will it adjust the overall pH when mixed with other components.
- It can be used alone or mixed with other media to create potting mixes.
- Great for seedling germination or plant propagation as the particles allow for plants to be pulled from the perlite without damage to the root systems when it’s time for transplanting.
- Reusable year after year since it doesn’t decompose.
- Low-cost option, perlite is cheaper than sand per cubic foot, costing about $4 or $5 per cubic foot.
- Easily available and simple to manufacture.
- Water can drain away quickly. Perlite holds water in the nooks found on its large surface area but since it’s made of amorphous volcanic glass it doesn’t hold it tightly.
- Being so lightweight, perlite can be blown away and tends to float in excess water.
- Nonrenewable resource. Although more readily available than peat moss, it isn’t considered renewable like coconut coir.
- Dust can create respiratory problems and eye irritation. When working with perlite make sure to take precautions by wearing goggles and a mask to reduce dust exposure.
Vermiculite vs Perlite
Growing herbs in perlite
I’ve talked about how perlite is useful for starting seeds, and rooting propagated cuttings because of its sterile nature and ability to drain excess water quickly. All herbs can be started using perlite as the sole growing media. When it’s time to pot up plants into containers while some herbs will thrive growing in only perlite, some herbs prefer other types of growing media.
Herbs that prefer drier, sandy soils that drain quickly will grow well in perlite.
- Lemon balm
Moisture-loving herbs such as basil, parsley, and coriander would grow better in a media other than perlite, one that holds onto more water.
Perlite vs other components
It’s commonly asked why perlite is so often used in gardening and if it is possible to replace perlite with other growing media products. The simple answer is that perlite is used often because of its low cost and extensive advantages. Also, there are common misconceptions about replacement products such as vermiculite or diatomaceous earth. These products are more complementary to perlite than useful as alternatives.
When you look at a bag of commercial potting mix you quickly notice the little white specks of perlite and the little gold pieces that almost resemble teeny tiny blocks consisting of plates or layers of material. These gold pieces are vermiculite, another very important product in gardening. Gardeners often think the two are interchangeable but that isn’t the case.
Vermiculite also comes from rock, and expands like perlite, but has a higher expanding potential. When heated it expands into an accordion-like shape composed of many, many layers of thin plates. It has a pH close to 7.0 but it fosters alkaline reactions because of carbonate compounds, so it has the tendency to slightly raise the pH in the root zone.
The biggest difference between the two products is that perlite helps increase the drainage, while vermiculite increases water retention by absorbing water in its plate-like structure. Use perlite when you are growing plants that benefit from the growing media drying out completely between waterings (succulents, orchids); use vermiculite when you are growing plants that prefer to be kept moist such as tropical plants.
In essence, perlite and vermiculite act as complements to one another versus alternatives.
Diatomaceous earth, or DE, is a naturally occurring, soft, siliceous sedimentary rock. It is another additive gardeners keep in their arsenal but it shouldn’t be used as a replacement for perlite for a few reasons.
- Like vermiculite, DE is more moisture-retentive than perlite so it helps to keep water in the root zone versus increasing drainage.
- Diatomaceous earth typically comes in powder form versus a granular. When mixed into garden soil as an amendment it doesn’t have the ability to reduce soil compaction like perlite does.
- When wet, DE has the tendency to clump together filling pore space. This doesn’t encourage or allow good airflow and oxygen movement to the plant roots.
Perlite is a valuable product in gardening and commercial horticulture. Expanded perlite is extremely lightweight and porous increasing the drainage capacity and allowing improved aeration in the root system when it is utilized. It can be used as a standalone growing media for starting seeds, rooting cuttings, or in hydroponic systems; it can be mixed with other ingredients to create soilless potting mixes; it can be used as a soil amendment in the garden.
Perlite; a great way to improve drainage (And a primer on what ‘organic’ means)
Q. Dear Mr. McGrath: My wife is an avid listener of your program, planning her Saturdays so that she can be home when your show is on. She suggested I contact you with my small concern that the perlite you often recommend isn’t “organic” in any sense that I recognize as a chemist—or probably in any sense that non-scientists use the word, as it is a form of glass http://www.perlite.net/. Now, this doesn’t take away from it being a useful component for gardening as you have advised; the advice is still fine. I would just suggest adjusting your justification of “it’s organic.” Oh, and rest assured that I am also a listener who enjoys your show. Keep up the good work!
—Harry in Havertown, PA
A. I have to thank Harry for bringing up an important point. In the world of technical chemistry, the word ‘organic’ has a very different meaning than it does in the world of contemporary food and agriculture. But that’s not unusual, as many English words have multiple meanings, like ‘bulb’, which can refer to an underground plant part, something that gives off light or even a squeezable thing, like the back end of a turkey baster. Context always reveals which version is in play (at least you hope it does, and people aren’t burying CFLs in their garden or screwing tulip bulbs into table lamps.)
Let’s take a look at the roots of the word ‘organic’ as we use it in modern gardening and grocery shopping. Back in 1940, J. I. Rodale, the founder of Rodale Press (now known as Rodale, Inc. or just ‘Rodale’) and originator of ORGANIC GARDENING magazine (titled “Organic Farming and Gardening” during its early years), chose ‘organic’ from a slew of words that the British were using to try and describe a form of agriculture that shunned the toxic chemical pesticides and fertilizers of the day; things like ‘arsenate of lead’ and ammonium nitrate—and later, famously, DDT. In its earliest and simplest uses ‘organic’ meant anything that occurred naturally—like seaweed, manure, rock dusts…
…and perlite, the misunderstood mineral. Harry is correct that perlite is a form of glass; specifically a volcanic glass that is mined and then heated in big ovens until it ‘pops’ into a round, white material that’s used in seed-starting and potting mixtures to lighten the soil, allow more air around the roots of plants and to both help retain water and improve drainage.
A lot of people think that those little white balls are some kind of Styrofoam-type artificial substance—heck, that’s what I thought they were my first couple of years gardening! But they are a mined mineral popped into little balls. Little balls that our bulb-happy friend Art Wolk (author of “Bulb Forcing for beginners and the seriously smitten”) has raved about on our show, during his lectures at places like the Philadelphia Flower Show, and in his publications.
One of Art’s missions as an educator is to beat the importance of air in the soil into gardener’s heads, whether they’re forcing bulbs in the ground or growing plants in garden beds—and perlite is a great way to do that. You may also recall that the great Four-Season farmer Eliot Coleman listed ‘air in the soil’ as one of his “three essential keys” in the seaweed piece we did a few shows back.
And I am proud to add that I personally use a lot of perlite. I buy a couple of big bags of it every season and mix lots into my seed-starting mixes>; however much perlite they already contain, I add more. And when I began to worry that the soil in some of my raised beds seemed to be getting a little heavy a few years back, I started mixing perlite into what’s otherwise now mostly 20 years of compost. And I add a lot of perlite to my garlic planting beds in the fall to make sure the bulbs don’t get waterlogged over winter.
And remember a few weeks back when we reported that Eliot Coleman said that seaweed was the only input he would buy if he didn’t live right near a cold ocean where he could get it for free? Perlite is my choice in that category. And since I don’t happen to live near an old volcano that’s conveniently located next to a giant oven, I do have to buy mine. And I buy and use more of it every year. “Air in the soil”; it’s a gardener’s second best friend. (After compost, of course!)
And you can be certain that it’s organic, because it’s a mined mineral; like rock dust and seaweed, it’s naturally occurring. It does need to be ‘popped’ but that only makes it more useful, not unnatural.
And you don’t have to believe just me…
…because it’s also officially organic.
In the early 1990s, the state of California did the hard work of making the first official decisions on what inputs and products would be allowed in what would come to be called ‘certified organic agriculture’. Shortly afterwards, the NOSB—the National Organic Standards Board—was formed to codify the Federal regulations that exist today. And part of that ‘standard’ is that all of the ‘materials’ or ‘inputs’ allowed in organic production must be on what’s called the “OMRI list”—the official listing of allowed products as issued by the Organic Materials Review Institute. Access their website, type in the name of the product or material you’re considering and it’ll give you a thumbs up or down.
And with perlite, the thumb is up: “Status: Allowed in certified organic agriculture; a mined mineral.”
Case closed. Now, where’s my big bag of perlite….?
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What Is Perlite Made Of: When and how to use it
admin February 4, 2019 1683 Views 0 SaveSavedRemoved 1
You will have seen perlite when you open up a bag of compost, all the little white specks mixed throughout the compost are pieces of perlite. In this article you will find out what perlite is made from, how, why and where you should use it in your garden.
What is perlite
Perlite – also known as expanded pyrite, is a form of amorphous volcanic glass, it is naturally occurring and is very lightweight and porous when processed. It is beneficial to use in gardening as it will keep your soil well aerated and drained and its porous nature helps to store nutrients.
What is perlite made of
Perlite is a form of volcanic glass which has a high water content, typically formed from the hydration of Obsidian. Perlite in its natural state is like a rock/glass. It is and brown/ black in colour before processing.
Processing is carried out by heating the rock/glass to very high temperatures- 1560-1650 Fahrenheit (850-900 Celcius) this causes the moisture inside the glass to turn to steam and expands the material from 7 to 16 times its original size- this steam expansion turns the perlite from a dense dark rock into a fluffy white lightweight product which we associate with the perlite we know. The material turns white due to the reflection of light bouncing off the surface of the expanded bubbles. Its nickname volcanic popcorn is well deserved!
How to use perlite in your garden
The main uses for perlite around my garden is for drainage. Because perlite is an expanded glass material it will not compact. When you add it to your soil or compost it keeps the soil structure from closing up and becoming dense.
Dense compacted soil will hold water within its structure and prevent the free movement of water through it, thereby stopping drainage. As mentioned before perlite can also help to hold vital nutrients within its cavities for your growing plants. A similar product- vermiculite can be used in the garden although it has very different properties.
Where to use perlite
Perlite can be added to potted plants, raised beds or mixed in with the soil in the ground. Perlite is a very useful and can be used in all applications around your garden and home. It allows the roots of the plants to grow uninhibited and provides a clear path for water air and nutrients to get easy access as the soil is not compacted, worms and other insects can enhance the soil further.
Perlite in hydroponics
Large or coarse grade perlite is very useful in hydroponics as a growing media and is great for starting stem cuttings as it allows the roots of the plants to uptake water and nutrients without becoming water saturated or getting root rot. See our article on how to use perlite in hydroponics.
What types of perlite are there?
Perlite usually comes in three size grades, fine, medium and coarse.
Coarse perlite is used more often in deeper soil cultivations such as raised beds or if the soil has strong water holding characteristics – clay soils etc.
Medium grade perlite is used more in larger potting applications or window boxes, fine grade is only really used with seed starting mixes or cutting mixes.
There are no hard and fast rules which grade you should use- if you are unsure and it is your first time to use it, a medium grade will usually be ok for most applications.
Where can I buy perlite?
You can buy perlite at any local gardening centre or home and garden store – or you can buy online.
I have listed the types i would recommend below. Click on the image or title for more information on Amazon.
Espoma PR1 1 Cubic Foot Organic Perlite
GROW!T GROWT JSPERL84 Perlite, 4 cuft 4 cuft White
Bonsai, Cactus & Succulent Pumice – Professional Sifted and Ready to Use American … (2.5 Dry Quart
If you have any questions please let me know in the comments section below. Thanks!
Perlite in the Garden: To Use or Not to Use?
Those small white particles we have all seen in potting mixes really do have an important role to play, though we may often take them for granted. They are called perlite and work to prevent the soil from becoming compacted.
By doing this, perlite functions as an aid to maintain adequate air or oxygen in the soil, which in turn improves plant respiration. To better understand whether perlite is right for your growing operation, it is best to look a bit deeper into just what it is and what it does.
Characteristics of Perlite
Non-combustible, perlite is essentially expanded glass that is retrieved from areas where a volcano has been active. Perlite is initially quarried, crushed, and then fractionated or divided up into its various parts: those that will be capable of being expanded into useful perlite, and those that are not.
The useful form of the product will have a typical grain size between 0.14 and three millimeters. These particles will later be expanded at high heat to give the final product its airy texture.
Perlite is non-fibrous, which makes it safe for use. However, it can contain perlite dust particles, so it is best to work with it moist to prevent the inhalation of these particles.
Nutrient-rich water is attracted to the small crevices in the perlite particles, and this capillary feature is why it can also provide moisture to your plants as well as aide in providing oxygen.
When is it Best to Use Perlite in the Garden?
Whether to use perlite or not greatly depends on what type of grow system is being used. Regular soil is an obvious candidate as it is quite heavy and can become compacted. Some organics like peat moss or coco mulch can and will also compact.
This happens over time as the soil or media is watered; each particle gets closer to the others and air pores are shrunk or eliminated. When this happens, water will not drain through the grow media very well and air will not easily penetrate. The grower will likely notice a decrease in plant vigor and production, though they may not be aware of the cause.
Roots also may fail to expand or grow, and they may contract various diseases due to a lack of oxygen and overabundance of moisture. Moss can grow on the medium’s surface if it remains wet most of the time.
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Perlite makes a positive contribution towards resolving these issues when used in the proper ratio. If your grow pots are sheltered from wind, perlite placed on the surface of the grow media will wick away moisture from the surface and reduce or eliminate mold and moss.
Perlite, however, is lightweight, which makes it problematic for grow systems where it might float. Deep water culture is an obvious one. With ebb and flow, the perlite particles may slowly travel towards the surface of grow pots, causing uneven distribution within the pot.
Any grow system where flooding is a part of normal operations may not be appropriate for using perlite.
Additional Tips for Using Perlite in Your Grow Medium
Though it is not a synthetic material, perlite can have a detrimental effect on the local ecological environment because it is strip mined. So, when buying perlite, it is worth researching the various firms that mine it and learn how they implement the maintenance of soil composition and ecology, and what steps they take to restore the environment. When done properly, there is no need to leave the landscape damaged after the mining process is finished.
As perlite does not hold much more than one per cent moisture, it is usually best used in conjunction with other materials. Vermiculite is a popular companion to perlite as it does hold considerably more water. In fact, vermiculite will hold from between 30 and 50 per cent of its volume in water, and 200 to 300 per cent of its weight.
When mixed 50/50 with perlite, it will do an excellent job of providing much-needed media porosity and air, as well as help to sustain plants from drought. If mixing perlite or vermiculite with peat moss, a combined ratio of between 25 and 35 per cent by volume is best.
The ability of perlite to improve aeration while it aids in providing water makes it an excellent product for many hydroponic applications. Perlite is a naturally occurring inorganic, chemically inert, and sterile product, so it does not represent a threat by adding unwanted biologics or pests into your system.
It is also an insulator so it can effectively reduce relatively high ambient air temperatures from transferring into the soil or media when used as a surface or lining product.
The question of whether to use perlite or not will first be decided by the type of system you are using. Some systems will not work well with it—mostly because it floats. Otherwise, this beneficial natural material can help to maintain a healthy root system by assuring that the soil or grow media stays porous and provides oxygen for root respiration.
Healthy roots mean greater yield and better-tasting crops. Any time you notice your grow media is becoming hard or compacted and seems to drain more slowly, you may want to incorporate some perlite into the mix.
Check out What Makes a Good Gardening Potting Mix? for more tips and tricks on mixing.
What Is Perlite: Learn About Perlite Potting Soil
Okay, so you bought the potting soil and have just planted a magnificent Ficus tree. Upon close inspection, you notice what appear to be tiny Styrofoam balls in the potting medium. Having heard of perlite, you may wonder if the little balls are perlite and, if so, what is perlite and/or the uses of perlite potting soil?
Perlite Soil Info
Appearing as tiny, roundish white specks amid the other components, perlite in potting soil is a non-organic additive used to aerate the media. Vermiculite is also a soil additive utilized for aeration (though less so than perlite), but the two are not always interchangeable, although as rooting mediums, both provide the same benefit.
Perlite is a volcanic glass that is heated to 1,600 degrees F. (871 C.) whereupon it pops much like popcorn and expands to 13 times its former size, resulting in an incredibly lightweight material. In fact, the end product weighs only 5 to 8 pounds per cubic foot. The super heated perlite is comprised of tiny air compartments. Under a microscope, perlite is revealed as being covered with many tiny cells that absorb moisture on the exterior of the particle, not inside, which makes it particularly useful in facilitating moisture to plant roots.
While both perlite and vermiculite aid in water retention, perlite is the more porous and tends to allow water to drain much more readily than vermiculite. As such, it is a more suitable addition to soils utilized with plants that do not require very moist media, such as cactus soils, or for plants which generally thrive in well-draining soil. You may still use a conventional potting soil that contains perlite; however, you may need to monitor watering more frequently than those made up of vermiculite.
When growing plants in perlite, be aware that it may cause fluoride burn, which appears as brown tips on houseplants. It also needs to be moistened prior to use to reduce dust. Due to perlite’s large surface area, it is a good choice for plants that require levels of high humidity. Evaporation off its surface area creates higher humidity levels than those of vermiculite.
Uses of Perlite
Perlite is used in soil mixes (including soilless mediums) to improve aeration and modify the soil substructure, keeping it loose, well-draining and defying compaction. A premium mix of one part loam, one part peat moss, and one part perlite is optimum for container growing, enabling the pot to hold just enough water and oxygen.
Perlite is also great for rooting cuttings and fosters much stronger root formation than those grown in water alone. Take your cuttings and place them in a Ziploc bag of moistened perlite, about one-third full of perlite. Put the cut ends of the cuttings up to the node into the perlite and then fill the bag with air and seal it. Put the air-filled bag in indirect sunlight and check it after two or three weeks for root formation. The cuttings can be planted when the roots are ½ to 1 inch long.
Other uses of perlite include masonry construction, cement and gypsum plasters, and loose fill insulation. Perlite is also used in pharmaceuticals and municipal swimming pool water filtration as well as an abrasive in polishes, cleansers and soaps.
When to Add Perlite Soil to Container Gardens
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What in the world is perlite soil anyway? Is it organic? I do a lot of container gardening, especially with my herb plants. Since I try to keep things all natural and as organic as possible, I looked into what makes perlite soil. The answer surprised me because I thought it was little bits of Styrofoam! Ick! But it is not. Perlite particles are actually totally natural volcanic glass particles that undergo a heat process to change form.
In addition to good mineral nutrient content, air is an important part of the soil mixture for any garden. Container gardens need air to keep the roots from being compacted by the soil. Perlite soil to the rescue! Volcanic glass is the basis for perlite soil. It is formed when heat is applied to the perlite component of ash and acts like popcorn. The perlite particles expand and pop, trapping moisture inside and adding air in the space between particles. It does have a similar appearance to the man-made Styrofoam but is an inert and sterile mineral.
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What is the Difference Between Perlite Soil and Vermiculite Soil?
Vermiculite is mined from silicate. It is commonly found in seed starting mixes and also plays a role in keeping moisture in the garden soil. It used to be more common to use vermiculite until asbestos was found in the mine in Montana. The industry changed its methods and vermiculite is still available. It has a strong moisture-retention ability without leading to fungus because of its spongy consistency. It is possible to use both vermiculite and perlite in your container gardening soil. Many gardeners prefer vermiculite for growing seedlings indoors and perlite soil for container gardening.
What Should be in Container Garden Soil?
Gardening discussions often center around the plants, but the soil is important too. Without good, nutrient-rich soil, your plants will not produce well, or at all. Nutrient-poor soil also contributes to weaker plants that are less disease and insect resistant. You do not need to use chemical or purchased fertilizer to add nutrients to the soil if you plan ahead. Although container gardens are a smaller scale production than a large garden bed, giving the plants the best soil will increase the production. If you are growing lettuce in containers or when growing flowers, starting with the right soil will help your results.
Compost for Container Garden Planting Mix
Compost is a great start when building soil and can be added to the container garden. In addition to the compost and garden soil, consider adding perlite for air. Many expert gardeners insist that air is one of the main components of healthy garden soil. The air provides oxygen, drainage and a lighter soil for deep root growth.
Using Peat Moss and Sphagnum Moss in Container Garden Potting Mix
Peat moss or sphagnum moss will help with moisture retention in the container garden. Garden soil lacks enough moisture, air and plant nutrition for successful growth and production. Adding peat or sphagnum mosses to the potting mixture helps change the composition enough to create the right soil for a container garden.
Should you Add Mulch or Wood Chips to Container Gardens?
Learning how to lay mulch in the garden helps with moisture retention and weed control. Mulching can also add to the nutrients in the soil over time. Susan Vinskofski, author of The Art of Gardening, Building Your Soil, states that using wood chips for mulch does not necessarily acidify the soil. Vinskofski regularly uses both hay and wood chips for mulch in her gardens. I think I will take her advice and start using mulch where I am growing vegetables in pots. I learned from Vinskofski’s blog posts that you need to make sure you push the mulch aside when planting and to not plant in the mulch layer itself but below in the soil. In addition, use no more than a couple of inches of mulch so that you can plant in the soil without having to dig through many inches of mulch.
Water Needs of Container Gardens
It has been my experience that my container gardens need to be watered far more frequently than my garden beds. The container garden itself is subject to heat and drying not only on the surface but also through the sides of the pot. During extremely hot weather, I need to water at least once a day. Sometimes I will carry some of the smaller containers to a shady spot during a heat wave. Overwatering has not been much of an issue for me but it has happened on occasion. The plant will wilt and die quickly if not tended immediately. When over-watering occurs, carefully take the plant from the water-logged container and replant in drier, well-draining potting mix. Set in a partially sunny location to help it recover. Under watering will result in browning, dry brittle plants that look unwell. Now that I have more knowledge of what the container garden soil should be, I would repot the plant using a better system that contains the peat moss and perlite soil for moisture retention and drainage.
Purchasing the Right Potting Mix for Container Gardens
If you don’t want to mix your own potting soil mix, there are many commercial types available. Most garden centers, plant nurseries, and home centers carry quite a variety of bagged potting mix. Knowing the soil facts concerning the difference between garden soil and potting mix is important. Now that I understand the different needs of container gardens, I can look forward to healthier producing plants in my garden. Have you added perlite soil to your container garden potting mix? Let us know in the comments below.
Originally published in 2016 and regularly vetted for accuracy.