According to the National Agricultural Library Thesaurus, winter sowing is defines as: A propagation method used throughout the winter where temperate climate seeds are sown into protective vented containers and placed outdoors to foster a naturally timed, high percentage germination of climate tolerant seedlings.
How is Winter Sowing Beneficial?
- Saves space and clutter in the home
- Saves having to buy equipment for indoor starting
- Reuse items you already have at home
- Starting from seed is cheaper than buying plants
- Grow interesting species of plants that garden centers don’t carry
- Saves the time and effort of hardening off your seedlings
One fallacy is that winter sowing prevents damping off. Damping off is a situation where fungus attacks a seedling and kills it. It’s common in indoor seed starting when conditions are not ideal and the seedlings are weak. It can happen outdoors too. The fungi, Rhizoctonia spp. and Fusarium spp., along with the water mold Pythium spp. are the most common pathogens responsible for damping off and are common in garden soils. With winter sowing, healthier seedlings are better able to survive these pathogens.
When to Winter Sow?
As it says, winter. Start too early, before the environment is fully cold, and you might get germination during a warm spell. Refreeze is likely to kill off your premature seedling. Winter sowing is intended for seed that need a period of cold stratification in order to germinate. Depending on the species, it can take as little as 3 weeks to as long as 3 months. Commonly, it’s 4 – 6 weeks. In zones 5 – 7, starting in January to mid-February is about right.
What Seed to Sow?
Species that are winter hardy in your zone are likely candidates. If the planting instructions on the seed packet says to pre-chill, that’s the perfect candidate for winter sowing.
Stratification is the process of exposing seeds to required periods of cold temperatures in order to break dormancy and germinate. In nature, at the end of the growing season, seed fall to the ground and overwinter there before germinating in spring. It’s a survival method; if they sprouted before winter, the seedlings would be too delicate to survive.
Scarification is another process that some seeds must go through before they can sprout. These are seeds with very hard, thick shells that need to be broken down. This might be accomplished by being scratched, nicked or digested by animals. Freezing can also cause them to weaken.
Some species that are suitable for winter sowing:
Flowers: Echinacea, Rudbeckia, Asclepia , calendula, coreopsis, cosmos, foxgloves, hollyhocks, petunia, snapdragon, bee balm and delphinium.
Vegetables: Herbs, beets, broccoli, cabbage, kale, chard, carrots, radishes, spinach, lettuce and bok choy.
How to Winter Sow
Winter sowing can be as easy as sprinkling seed onto the ground where you want them to grow. This is the best option for species that do not like having their roots disturbed by transplanting. Poppies, foxgloves and Asclepia ssp. (Milkweeds) are amongst these.
This method is called direct sowing. Seed packets will indicate if direct sowing is recommended.
Sowing in containers can be more rewarding, if direct sowing is not specifically recommended.
Containers provide:
- Protection for your seed from being scattered, disturbed or eaten
- Quicker soil warmup and germination when temperatures start to rise
- Extra warmth and protection for your seedlings to grow faster
Most know about using milk jugs, but anything with:
- Lid that is transparent or translucent to let in light. You’re basically making tiny little greenhouses.
- Material that can withstand cracking
- Material that you can poke or cut holes in for water and air flow. Make enough holes on the top to let in water and for air circulation; enough holes at the bottom so water can flow out freely. If you are cutting jugs or bottles in half, you don’t have to completely seal it back together with tape. Less tape is easier to remove, so that you don’t struggle and damage the seedlings.
- Enough space for the number of plants you want and height for the species that you are growing. Species that grow tall will also have deeper roots. If your containers are too small, you may have to transplant more delicate young seedlings earlier.
If you have a smaller garden and only want a few plants, consider planting in soda bottles or groups of small pots in a milk jug or takeout container. Label each pot.
Label the container lid before planting your seed. Paint pens work better for labelling because they are more resistant to fading. But if you’re watching regularly, touching up permanent marker works. I like to write over clear tape, so that I can peel off the tape and reuse the container, year after year.
Also stick a label in the container before you plant the seed. That will come in handy when you transplant and also acts as insurance if the outer label vanishes.
Potting mix is a good growing medium. Garden soil works, it’s just heavier for baby roots to fight through and may contain more diseases and pests. Bigger plants will need at least 3”, tiny plants (thyme, for example) can do with 2”. The longer you want to leave them in the container to grow, the deeper your soil needs to be.
Moisten the mix before you fill your container. Lightly moist, not dripping wet.
Seed are mostly shallow or surface planted, for species that require winter sowing. Check the seed packet for instructions. If you plant too many seed, too close together, you may damage the seedlings when you try to separate them for transplanting. Space larger seed with about ¼” between them; poke shallow holes and drop them in. If seed are tiny, sprinkle sparingly over the surface and lightly press them into the potting mix. If you can’t resist covering them, just the thinnest sprinkle of potting mix will do.
There’s no need to water. If it’s too wet, your seed may rot.
Location is important. Place them where they can get sunlight and rain. You may also want to protect them from strong winds and animal tipping them over.
Start checking for growth around St. Patrick’s Day. As the seedlings get bigger, the lids will need to be removed periodically for more light and air circulation. Your little greenhouses may also overheat and cook your little seedlings if temperatures rise over 50F.
Transplant when the seedlings have at least 2 pairs of true leaves above the first leaves from germination. It’s good to leave them as long as you can, to toughen them up to survive transplanting. However, don’t wait so long that the roots are so tangled together that you end up damaging them while prying them apart.
Containers that work better
Here are products you might use, instead of just recycled containers. They allow better control over the process and are easier to manage if you want to speed up the process and bring them inside to warm up faster, after the cold stratification period. Tie the lids on to withstand the elements; taping leaves residue and has to be reapplied whenever you open to check.
The 12 cell containers work well for those who just want a few plants of each species and want to skip some of the work of picking seedlings apart. Just place a couple of seed per cell, or a very light sprinkle of tiny seed.
Color can matter. Roots are meant to grow in the dark, in soil. However, with clear inserts, you can watch root growth and keep them in dark watering trays. Green, to me, is more attractive, but not as dark for roots as black.
Each photo proves links to more information on the item.
- Assorted sizes is a good choice because of the options for different growing needs. The larger trays have higher domes for better ventilation when growing taller seedlings.
- Small set with high domes is a 10 pack of 12 cells each.
- Top right is the cheapest and works very well. I’ve reused a similar set for over 6 years.
- White set costs a little more, but those are good tools for seed/seedling management. and worth the extra few dollars, if you don’t already have them.
- Small pots can also be replace the 12 cell inserts. This works well for adding new batches of seed to a tray. Just keep note of the different dates that they started chilling.
There are many more options, but from my 20+ years of experience seed starting in the home, these are my top picks for economy and effectiveness.
