URBANA, Ill. – Winter-sowing is a cost-effective and low-maintenance way of starting plants for the garden. Creator of the winter-sowing method, Trudi Davidoff puts it in simple terms: starting plants outdoors, in winter. 

“Winter-sowing works with nature to prepare seeds for growth by providing the proper conditions to begin germination. While this may sound complicated, the only supplies needed are a recycled container that allows light through, soil, and seeds,” says Nicole Flowers-Kimmerle, horticulture educator with University of Illinois Extension.

To begin, create your miniature greenhouse from recycled plastic containers. Milk jugs that allow light to penetrate work well. Experiment with the recyclable containers you have on hand. 

Miniature greenhouse made from recycled plastic container

Because the containers will collect snow and rain, add drainage holes in your mini-greenhouse. With a drill or utility knife, cut several holes into the bottom of the container. Cut around the milk jug below the bottom of the handle, without cutting the top of the container all the way off. Leave about a half an inch intact just below the handle. This section acts as a hinge to hold the container together.

Next, fill the bottom of the miniature greenhouse. Moisten the soil and allow it to drain. The soil should have a moisture level like a damp sponge. Light and fluffy soil that drains well works best.

The container is now ready for seeds. Small seeds can be left on top of the soil, however larger seeds require more attention Follow the instructions on the seed packet for planting depths of larger seeds. Make sure there is good contact between the seed and the soil. Replace the lid and secure with duct tape. Label the container with the date and the type of seed planted. Your small greenhouse container is ready to go outdoors. While the mini-greenhouses should receive sunlight and have exposure to rain and snow, they should be placed in an area that is safe from strong winds

The temperature variation prepares the seeds for germination at the proper time. When the days begin to warm, seedlings will emerge. After emergence, open the container on sunny days, but close it at dusk to protect the seedlings from cold night temperatures. The seedlings naturally harden off and can be transplanted when soil temperatures reach proper levels. Cut flaps along the side of the miniature greenhouse to slide seedlings out. Divide the clump into pieces and plant as you would a store variety.

Wait to begin winter-sowing until January or February. If there is a warm spell, the seeds can germinate, but won't be hardy enough to survive when temperatures fall.

“Do your homework when choosing seeds,” Flowers-Kimmerle says. “Frost-tolerant flowers and vegetables such as petunias, cosmos, kale, broccoli, spinach, and Brussels sprouts successfully withstand the cold temperatures of early winter. Frost-sensitive species such as zinnias, tomatoes, and squash need to wait until the warmer temperatures of March or April before sowing using this method.”

Winter sown seedlings grow into healthy, sturdy plants. Plants will be ready to thrive in the garden when spring arrives.

News source/writer: Nicole Flowers-Kimmerle, 309-547-3711, nflower2@illinois.edu