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Springtime starts in February and March with winter sowing. With winter sowing, temperate climate seeds may be planted in containers and set outside to experience natural conditions to stimulate germination. This nature-inspired approach can be used to grow vegetables, flowers, and even fruiting plants like strawberries – all without refrigerating seeds, special schedules, or equipment like grow lights.
In fact, reusable containers, tape, seeds, and potting soil are all you need to get started. In addition to higher germination rates, winter sown seedlings become healthy, sturdy plants that do not require hardening off and will be ready for your the garden when spring finally arrives.
When to winter sow
Winter sowing considers our hardiness zone’s average frost free dates. Try to winter sow prior to the first frost free day. For cool weather crops and those needing a chilling period or cold stratification, sow four to six weeks before the first frost free date.
- Northern Illinois is covered by Zone 5a (far northwest) or Zone 5b (rest of the counties) – Frost-free date: May 1-10
- Central Illinois spans zones 5b and 6a – Frost-free date: April 11-30
- Southern Illinois includes zone 6a, 6b and 7a – Frost-free date: April 1-10
The recommended months for northern Illinois are February to April starting with cool crops, perennials, and hardy annuals in February and March, and warm weather crops and flowers in March and April. Some sow earlier, some sow later.
How to winter sow
Protected, vented containers allow precipitation in and drainage out. Use milk jugs, old food containers, or bins. The key is to have openings on the top for precipitation, openings on the bottom for drainage to prevent flooding, and a covering to create condensation and to imitate a mini greenhouse.
The following suggestions will help you winter sow successfully:
- A sunny location will create warmth and humidity.
- Potting soil provides drainage and a limited amount of nutrition. Later seedlings will need diluted liquid fertilizer.
- You can add perlite to potting mix to improve drainage and aeration.
- Avoid moisture retention soil and fertilized soil mixes which can lead to algae growth.
- Do not use soilless growing mixtures.
- Moisten the soil at the start and monitor moisture levels until seedlings are transplanted.
What to winter sow
Donna Aufdenberg, field specialist in Horticulture at University of Missouri, provides a step-by-step approach and recommends winter sowing the following plants:
- Perennial flowers: dianthus, phlox, gaillardia, Shasta daisy, poppy, salvia
- Native plants: milkweed, black-eyed Susan, purple cone flower, liatris, lobelia, penstemon and countless others (check seed packet for more information on how long different natives need to be stratified as some will need to be planted earlier)
- Cool season annuals: snapdragon, pansy, nasturtium
- Cool season vegetables: broccoli, cabbage, cauliflower, lettuce, kale and spinach
- Warm season vegetables: tomatoes, peppers, zucchini, cucumbers
- Herbs: oregano, marjoram, thyme, chives, basil, parsley
This is not an exhaustive list but provides a sample of the types of plants that can be winter sown. Do not forget fruiting plants like strawberries, which can be winter sown from seed. Interested in learning more about Winter Sowing, visit extension.illinois.edu/blogs/over-garden-fence/2024-01-15-how-try-winter-sowing or extension.illinois.edu/news-releases/chase-away-those-winter-blues-four-seasons-gardening-webinars.
• Evonne Waters is a University of Illinois Extension Master Gardener serving Kane County. Water’s primary areas of expertise are deconstructed square-foot gardening, winter sowing methods and chaos gardening. Evonne is a member of the Community Collaborative Rain, Hail and Snow Network.
Have a question for the Master Gardeners? Residents can contact the Master Gardener volunteers March through October. Learn more at go.illinois.edu/HelpDeskMGdkk.