Labeling the seed type is important; duct tape marked with a permanent marker works well. With covers securely in place, the containers are placed in the snow under Mother Nature's care.
Why does winter sowing work?
Many seeds only become viable after exposure to chilling temperatures. The winter months naturally provide this vernalization, this necessary cold-temperature treatment that promotes flowering.
Winter sowing is an ideal germination method for perennial and hardy annual seeds. It is especially effective for herbs such as parsley and oregano, cold germinating vegetables like spinach, chard and kale, alpine species and biennials like hollyhocks which need two seasons to produce flowers.
What seeds should you choose?
Trudi Davidoff, who is credited with discovering winter sowing, offers advice on how to read the clues given in seed catalogs. Terms such as "Needs Pre-chilling (freeze seeds, refrigerate seeds, stratify for x amount of days or weeks), Needs Stratification, Will Colonize, Self-Sows, Sow outdoors in early Autumn, Sow outdoors in early Spring while nights are still cool ..." are all clues that the seed type is appropriate for winter sowing. You can find much more advice about seed selection at the excellent website, WinterSown.org. Do remember to consider your hardiness zone when choosing seeds.
Winter sowing does require a little organization; not all plants need to be sown at the same time. Kevin's updated post on A Garden for the House offers good advice on the best time to sow specific plants.
Winter sowing is definitely something new for me. Like any new gardening approach, it calls for a little research and a little experimentation. The USDA describes this method as a way "to foster a naturally timed, high percentage germination of climate tolerant seedlings." What could be better for our northern gardens? Why not give it a try?
- Ensure container depth is 5" or more to accommodate soil, roots and seedlings.
- Add holes to the bottom of the container to ensure proper drainage.
- Planting soil should feel moist but not wet, otherwise it will freeze when placed outdoors.
- Label carefully, both inside and outside.
- Once containers are set in the snow, rest a board on top to protect against wind and animals and cover well with snow.
- Ensure that containers are always in contact with the snow.
- If the soil becomes too soggy, add more drainage holes to the bottom and elevate the container.
- Once the seeds germinate and daytime temperatures rise, open the containers, but monitor carefully for moisture and freezing temperatures. Close to protect plants at night.
- Use a watering can with a rosette (80 holes or more) or a hose attachment set on mist to provide water to seedlings.
- Monitor for slugs on the containers. Elevate on a palette or in a tray of chicken grit if slugs are evident.
Browse or post a question on the Canadian Winter Sowing forum on GardenWeb.com.
What is your experience with winter sowing? Please share in a comment.