Most gardeners know about the two main ways to start seeds: either plant them directly into the soil, or start them early indoors to and transplant later. Much less familiar is “winter sowing” —starting seeds early outdoors with just enough protection to allow germination.
It doesn’t work for all vegetables or flowers, but winter sowing is easy enough and sufficiently low-cost that it’s worth a try for varieties that don’t mind a bit of cold. The technique gives at least a few weeks head start to the season without the lights, soil spills, watering issues and other possible pitfalls of indoor seed starting.
Here’s how to do it in 6 steps
- Start with rinsed-out plastic beverage containers—either gallon or half-gallon ones, depending on how many plants you want. Translucent containers let in enough light for germination and good seedling growth, yet are enclosed enough to give a few degrees of extra warmth.
- Use a sharp knife to cut the containers horizontally about halfway up and most of the way around. Don’t cut at the handle. Let the containers become “flip tops” that can open and close.
- Cut small holes at the base of each corner for drainage. A ballpoint pen, a heated, half inch nail or an ice pick works well.
- Add about 4 inches of dampened, light-weight container or seed-starting mix to each container and water. When the mix drains, you’re ready to plant.
- Bigger seeds can be pushed in one at a time. Smaller ones can be scattered and lightly tamped into the mix. Don’t forget to label each container so you know what’s in each one.
- Set containers outside without their caps to let rain in. Use a couple pieces of duct tape placed vertically to keep the containers from blowing open in the wind.
In most cases, seeds can be winter-sown in containers 4 to 8 weeks before they’d normally be sown unprotected in the ground. Experiment with start times. The germination and cold-hardiness of seeds varies widely from species to species. Expect the seeds to take longer to germinate outside than inside.
Window wells, empty beds along a heated wall and cold frames made out of lumber and plastic or glass are all good places to set winter-sowed containers—at least in the early going. As the weather warms and the seedlings grow, the containers can be moved more out in the open, such as on a deck or patio.
On mild days, raise the tops of the containers to allow more light to reach the tiny seedlings. Close them at night. If the weather is dry, sprinkle the containers occasionally to keep the container mix damp.
Winter-sown plants won’t need to “harden off,” unlike with indoor-grown seedlings. When the time comes to plant unprotected in the garden, the containers will be filled with young seedlings that are already acclimated to the air and light of the outside.
Some of the best annual flowers for winter sowing: Sweet alyssum, snapdragons, California poppy, larkspur, annual phlox, blue woodruff, calendula, flax, cornflower, browallia, larkspur, linaria, nigella, and Joseph’s coat. Start these indoors until temperatures rise: Cosmos, diascia, sunflowers, ageratum, marigolds, nicotiana, celosia, cleome, and zinnias.
Some of the best perennial flowers for winter sowing: Aster, astilbe, baby's breath, gaillardia, liatris, coreopsis, gaura, penstemon, phlox, black-eyed susan, coneflower, Shasta daisy, yarrow, carnation, coralbells, baptisia, hollyhock, salvia, veronica.
Some of the best vegetables and herbs for winter sowing: Parsley, mesclun, lettuce, Swiss chard, cabbage, broccoli, cauliflower, kale, collards, spinach. Start tender herbs and vegetables indoors until temperatures rise, including: basil, dill, tomatoes, eggplant, and peppers.