When to start planting?

Zone 4 Seed Starting: Learn When To Start Seeds In Zone 4

Winter can quickly lose its charm after Christmas, especially in frigid areas like U.S. hardiness zone 4 or lower. The endless gray days of January and February can make it seem like winter will last forever. Filled with the hopeless, barrenness of winter, you may wander into a home improvement or big box store and find delight in their early displays of garden seeds. So when exactly is too early for starting seeds in zone 4? Naturally, this depends on what you are planting. Continue reading to learn when to start seeds in zone 4.

Zone 4 Seed Starting Indoors

In zone 4, we can experience frost sometimes as late as May 31 and as early as October 1. This short growing season can mean that some plants will need to be started from seed indoors several weeks before the last expected frost date in order to reach their full potential before autumn. When to start these seeds indoors depends on the plant. Below are different plants and their typical planting times indoors.

10-12 Weeks Before Last Frost


  • Brussel Sprouts
  • Leeks
  • Broccoli
  • Artichoke
  • Onion


  • Chives
  • Feverfew
  • Mint
  • Thyme
  • Parsley
  • Oregano
  • Fuchsia
  • Pansy
  • Viola
  • Petunia
  • Lobelia
  • Heliotrope
  • Candytuft
  • Primula
  • Snapdragon
  • Delphinium
  • Impatiens
  • Poppy
  • Rudbeckia

6-9 Weeks Before Last Frost


  • Celery
  • Peppers
  • Shallots
  • Eggplant
  • Tomatoes
  • Lettuce
  • Swiss Chard
  • Melons


  • Catmint
  • Coriander
  • Lemon Balm
  • Dill
  • Sage
  • Agastache
  • Basil
  • Daisy
  • Coleus
  • Alyssum
  • Cleome
  • Salvia
  • Ageratum
  • Zinnia
  • Bachelor’s Button
  • Aster
  • Marigold
  • Sweet Pea
  • Calendula
  • Nemesia

3-5 Weeks Before Last Frost


  • Cabbage
  • Cauliflower
  • Kale
  • Pumpkin
  • Cucumber


  • Chamomile
  • Fennel
  • Nicotiana
  • Nasturtium
  • Phlox
  • Morning Glory

When to Start Seeds in Zone 4 Outdoors

Outdoor seed planting time in zone 4 is usually between April 15 and May 15, depending on the specific plant. Since spring in zone 4 can be unpredictable, pay attention to frost advisories in your area and cover plants as needed. Keeping a seed journal or seed calendar can help you learn from your mistakes or successes year after year. Below are some plant seeds that can be sown directly in the garden from mid-April to mid-May in zone 4.


  • Bush Beans
  • Pole Beans
  • Asparagus
  • Beet
  • Carrot
  • Chinese Cabbage
  • Collards
  • Cucumber
  • Endive
  • Kale
  • Kohlrabi
  • Lettuce
  • Pumpkin
  • Muskmelon
  • Watermelon
  • Onion
  • Peas
  • Potatoes
  • Radish
  • Rhubarb
  • Spinach
  • Squash
  • Sweet Corn
  • Turnip


  • Horseradish
  • Morning Glory
  • Chamomile
  • Nasturtium

4 Steps to Figuring Out When to Start Seeds Indoors

For slow maturing plants and gardeners with short growing seasons, starting seeds indoors can be a crucial element to achieving success. To figure out the optimal time to start your seeds indoors, all you really need is a bit of backwards thinking.


Step 1: Getting Into Your Zone

Hardiness Zone maps are geographic divisions based on the average minimum temperatures of a particular region. For gardeners, knowing what zone you are in is key to knowing which types of plants will grow successfully in your area. Using hardiness zones to grow plants is not an absolute science, the maps are meant as a guide. Environmental stressors, cultivation techniques and artificial environments like buildings and elevated decks are all factors that play into whether a plant can be ‘pushed’ beyond its normal zone.

To find your zone in North America, visit the National Arboretum’s website at:

  • USDA Plant Hardiness Zone Map

International gardeners can find maps of their zones here:

  • North American Hardiness Zones

Step 2: Finding Your Last Frost Date

Now that you know your Hardiness Zone, you will need to find the average last expected frost date for your zone. If you live outside of North America, you can either compare your zone to the equivalent North American zone that matches your average lowest temperature, or check with your national climate data center.


Average Dates of Last Frost
(North American Zones)
Zone 1: June 1-June 30
This zone remains vulnerable to frost 365 days per year.
Zone 2: May 1-May 31
Zone 3: May 1-May 31
Zone 4: May 1- May 31
Zone 5: March 30-April 30
Zone 6: March 30-April 30
Zone 7: March 30-April 30
Zone 8: February 28-March 30
Zone 9: January 28-February 30
Zone 10: January 30 or before.
Zone 11: Frost-free year round.

As you can see, the above list illustrates a 4-week range of potential last frost dates for each zone. Many gardeners in lower zones like to use the earliest dates in the range. This is probably a good strategy if your growing season is on the shorter side. Higher zones may want to start seeds somewhere in the middle of the 4-week period. No matter what your zone, make sure you factor in an extra week for hardening seedlings off before moving them permanently outdoors.


To get the best picture of trends on your area, contact your county extension agency, or ask a local nursery. The best way to calculate the last average frost date for YOUR garden is to keep a journal and watch the trend over several seasons.

Step 3: Find the Number of Weeks Until Transplanting

The amount of time it takes from planting to maturity will vary greatly depending on the type of seed you are planting and what type of growing conditions you provide for it (soil, light, and water). New seed packages should tell you on the back the average number of weeks before the last frost they should be planted. Remember, the numbers given always assume that you will be providing optimal growing conditions. If your seeds didn’t come information on how far in advance to sow them, use the chart at the end of this article as a guide:


Step Four: Think Backwards

Once you have your average last frost date and know how many weeks before it your seeds should be planted, simply find your last average frost date on calendar and count backwards the number of appropriate weeks and you’ll have your date. Remember, when sowing seeds indoors, it’s usually better to be too late, than too early. Start seeds too soon and you may end up with weak, spindly plants that can’t hold up in the garden.

Plant Number of Weeks Before Last Frost to Start Indoors
artichoke 10-12
ageratum 8
alyssum 8
aster 6
balsam 6
basil 6-8
batchelor button 4-6
begonia 12 or more
broccoli 8
browallia 12 or more
brussels sprouts 7-8
cabbage 5-7
cauliflower 8
catnip 8-12
calendula 6-8
cantaloupe 3-4
celery 7-12
celosia 8
centurea 8
chamomile 8-12
chervil 6-8
chives 12-14
coleus 8
collards 5-7
columbine 8
coriander 6-8
cosmos 4
cucumber 4
dahlia 8
daisy 6-8
dianthus 10
dill 6-8
eggplant 8
feverview 8-12
fuchsia 18-20
geranium 12 or more
impatiens 10
kale 4-6
lemon balm 6-8
larkspur 12 or more
leeks 10-12
lettuce 8
lobelia 12-14
marigold 6
mint 12-14
muskmelon 4
nasturtium 4-6
nicotiana 8
okra 2-4
onion 10-12
oregano 12-14
pansy 12 or more
parsley 12-14
peppers 8
petunia 10
phlox 8
poppy 12-14
portulaca 10
pumpkin 2-4
sage 6-8
savory 6-8
snapdragon 10
spinach 6-8
squash 4
stock 10
Swiss chard 6-8
thyme 8-12
tomato 6
verbena 10
vinca 12 or more
watermelon 5-6


Tip: Don’t discard your half-used seed packets from last year! Many of them will stay viable for several years if your keep them stored in a cool, dry place. Here is a brief list of the life expectancy of some common vegetable seeds.

Plant Seed Life Exptectancy
beans: 3 years
beets: 4 years
broccoli: 3 years
cabbage: 4 years
carrots: 3 years
cauliflower: 4 years
corn: 2 years
cucumber: 5 years
eggplant: 4 years
lettuce: 4 years
onions: 1 year
peas: 3 years
peppers: 2 years
radishes: 5 years
spinach: 3 years
squash: 4 years

Starting Seeds indoors:  Tomatoes and Pepper Seeds in January!?

by Karen of Love Your Land

with Sharon Peterson

I’m a native of California, so when I moved to Colorado and began gardening in this beautiful, four-season climate, at the end of my first season, to say I was sad is an understatement. Hadn’t it just started?

Seed Starting Class

Check out this Course on Starting Seeds Indoors. My friend Rick does a great job going over all the supplies needed, types of lights and how to handle your seedlings.

Seed Starting Simplified.

My first and biggest mistake was to assume that if I followed the growing guidelines on the back of my seed packets, I would have optimum yields. I failed to recognize that seed packets are simply not written for individual zones. So while it was technically acceptable for Starting Seeds indoors, indoors 4-6 weeks before the last frost, transplanting 8-inch tall tomato seedlings on June 1st and expecting them to grow, mature, flower, set fruit, and have the fruit ripen in 3 months was delusional.

Once September hit, we already had frosts in the forecast. So there I was, picking all of my green (and small) tomatoes off my plants, and bringing them inside to (hopefully) ripen them in a cardboard box with newspaper. (This isn’t nearly as satisfying for the gardener as it may sound.)

Months later (December 29th, to be exact), I took the bull by the horns and started my tomatoes and peppers inside – a full 6 months before they were to be transplanted outside. This was the best thing I ever did for my garden, and myself.

So how do I do it? Following are 6 very simple steps to starting your own garden, from seed, inside, in winter! Starting Seeds indoors.

Step 1: Prepare your grow room (or grow ‘space’)

In December or January (no later than early February), I begin starting seeds indoors by setting up my grow space in a large, south-facing window. The first step in preparing my grow space is making the epic journey, through the snow, to my shed outside, to gather supplies, which includes my grow racks, small (2”x 2”) seed starting pots, plant markers, and my handy dandy spray bottle.

Inside, I tape a double layer of plastic to the floor to protect it (it’s going to get messy in here), then assemble my grow racks on top. They won’t be holding pots for a while, but will instead hold my supplies, give me additional work space, and when the seedlings are ready for big pots, they’ll be ready for action.

Step 2: Prepare your planting medium

seeds are already starting in this pot

Next, I get my planting medium ready. What’s a planting medium, you ask? It’s whatever you choose to grow in – be it potting soil, rehydrated coir, organic soil, sterile soil, etc. My planting medium is one part sterile soil, one part rehydrated coir, and a handful of vermiculite. I put all of this in a big, storage tub with a lid, and mix it up with my hands (and arms). (This might just be my favorite part of the process.)

Step 3: Starting Seeds indoors

I take a large bowl or a bucket, and fill it about three-quarters full of the soil mixture, water the soil, and mix thoroughly. I pre-water my soil so that once I add my seeds, I won’t need to disturb them by pouring water over them.

I take my tiny seed starting pots, and fill them with my pre-watered soil mixture. Ever so slightly, I press the soil down with the back of my fingers, mainly so that I know it’s full and there are no big soil-less pockets. Do not press hard!

Drum roll, please! Finally … I add 3 seeds (of the same variety) in a triangular placement on top of the soil. The rule of thumb for the depth in which to plant your seeds is … as deep as their size. This means, tiny seeds like tomatoes, peppers, and basil need only be placed on top of the soil, and then a sprinkling of soil goes on top, only to ensure they are in full contact with the soil on all sides.

Once you’ve placed your seeds on top of the soil, and sprinkled a bit of soil on top of the seeds, again, press the soil ever so slightly, again, only to ensure full contact between seeds and soil.

Don’t forget to mark your pots! Just like when our kids are little, we think we’ll never forget this moment. Trust me, in about 5 minutes, you won’t be able to tell one pot from the next. Label them as you go, or better yet, before you even put seeds in them.

Step 4: Germination

When I begin starting seeds indoors, I place my tiny pots in a seed starting (humidity) dome. It keeps the seedlings warm, keeps the moisture level consistent, and prevents the soil from drying out too quickly. It also has a light, but seeds don’t need light to germinate. However, once they germinate, then they’re seedlings, and seedlings must have light to grow. (And no, the light from the south-facing is not enough.)

In my experience, this protective little dome speeds up germination. However, each type of seed is going to germinate at a different rate. Using this dome, I usually see the first signs of germination of tomatoes and peppers in about 4 days. Which, of course, is the happiest day of the year (so far) for us gardener types.

Step 5: Watering & Feeding

Before your seeds have germinated, I do not recommend pouring water in the pots. Again, you will be disturbing the seeds, and they may lose contact with soil. Instead, I use a spray bottle. About every other day, I spray the top of the soil (and because I’m weird, I give each pot exactly 12 sprays – I don’t know why, it’s just what I’ve always done, and it works for me).

Once your seeds germinate and your seedlings are at least a few inches tall, then you can begin watering them by pouring the water in the pots. But be very careful – they are very delicate in this stage.

And DO NOT over-water. This can lead to dampening off, which is basically cutting off their oxygen supply, and will kill them. Instead, poke your finger into the soil to check for moisture. If the soil is bone dry, give them some water (and maybe check on them more often). If the soil is moist, hold off on watering, and check again the next day. In fact, letting the soil dry out a bit in between waterings will force the roots to go deeper and wider in search of water (making them stronger), and will also reduce the risk of the soil developing surface mold and other diseases.

Once your plants have their second set of true leaves, they’re going to need to be fed. (They DO NOT need to be fed as seeds or newly germinated seeds.) However, young seedlings can’t handle full doses of fertilizer, so I recommend diluting it or cutting it in half. Look for an organic fertilizer that’s right for your type of plant, and feed them about once a week. (And remember, any plant held captive in a pot needs to be fed. It has no way of searching out nutrients in surrounding soil, so it needs your help!)

Step 6: Pruning

Here’s a tip!

When you cut off the grow tip, place it in a cup of water, let it root, and after a couple of weeks, plant it in a pot! Free plants!

Plants such as tomatoes and peppers benefit greatly from pruning. And frankly, so will your grow room/space, because after a couple of months, your plants are going to be getting mighty big.

So … once the main stem is at least as thick as a pencil, and the plant is about 10 inches tall, it’s time to start thinking about pruning. I recommend snipping off the grow tip at this point, which means cutting just above the juncture at the third or fourth set of leaves. This will force side shoots to grow out horizontally, and your plants will be stronger and better prepared for outside life when the time comes. (The rule of thumb for tomatoes and peppers is, you want them wide and strong as opposed to tall and gangly.)

You can count on needing to prune them about every other week until it’s time to transplant them into your outdoor garden.

A Note about Flowering and Setting Fruit

If you start your tomato and pepper seeds inside as early as I do, and assuming things go well, you can bet at least some of the plants will be flowering weeks before you put them outside. In fact, I consistently have tons of fruit on the plants before I ever set them out as well!

And no, I don’t have bees in my house. On a small scale like this, you can hand-pollinate your flowers! (Just take care not to cross-pollinate.) You can either use your finger to go from one flower to another, or you can gently shake the plant. (Gently, I say!) Do one of these things every day, and I can all but guarantee you will have tomatoes and peppers on your plants, inside your house, before a bee ever lays eyes on them. How cool is that?!

So, start your seeds today! You’ll be glad you did, I promise! It truly is something special to watch a single, tiny seed come to life and grow, and then to know those tomatoes in your salad came from that single, tiny seed. It truly is a miracle.

Happy Gardening, Everyone!


Video with Karen planting and starting seeds indoors.

Karen is a wife, mother, business owner, gardener, canner, and the owner of “Love Your Land.”

Karen understands that gardening in Northern Colorado is seemingly a fleeting moment in time, so join her on Facebook for daily tips, tricks, and discussions, and on Love your Land You Tube for weekly how-to videos on how to extend a 3-month grow season into a 9-month grow season!

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