If you haven’t tried winter sowing flower seeds, you may be surprised that you can sow seeds in small, homemade greenhouses and let the containers sit outdoors all winter, even if your climate sees more than its fair share of freezing temperatures, rain, and snow. Even more surprising, winter-sown plants tend to be stronger and more resilient than indoor-sown seeds. This winter sowing guide will help get you started.
How to Winter Sow Flowers
Save a few translucent or clear plastic containers for sowing flower seeds in winter. Milk or water jugs work well, or you can use 1-liter (1 qt.) soda bottles or similar containers. Use a sharp craft knife to cut the bottles around the middle, but don’t cut completely around the jug – instead, leave a small uncut area to work as a “hinge.” Punch several holes in the bottom of the jug because your winter-sown seeds will rot without drainage.
Fill the bottom of the container with 2 to 3 inches (5 to 7.5 cm.) of any lightweight commercial potting mixture, or use a combination of half perlite and half peat moss. Water the potting mix thoroughly, then set the container aside to drain until the mix is evenly moist but not dripping wet.
Sprinkle your seeds on the surface of the moist soil. Cover the seeds according to the planting depth recommended on the seed package, then pat the seeds lightly into the soil. Close the hinged container, secure it with duct tape, and label the containers clearly with paint or a permanent marker. Don’t put lids on the containers.
Set the container outdoors, in a location where they are exposed to sun and rain but not too much wind. Leave the containers alone until you notice seeds germinating in early spring, usually while nights are still frosty. Open the containers, check the potting mix, and water lightly if needed. If days are warm, you can open the tops, but be sure and close them before nightfall.
Plant the seedlings in your garden when they’re large enough to survive on their own, and when you’re sure all danger of frost has passed.
Flowers for Winter Sowing
Hardy plants can be sown as early as January or February. These include flowers such as:
Suitable vegetables for winter sowing include:
Tender, extremely frost-sensitive plants (i.e. tomatoes) should be planted after any danger of a hard freeze has passed – often as late as May if you live in a chilly climate.
If an unexpected late freeze is predicted, you may want to move the containers to an unheated garage or sheltered area during the night. Don’t bring them into a warm indoor climate.