What is Winter Sowing?
During the winter months we can not only dream about the flowers and vegetables that we want to add to our gardens next spring, but we can also actually start those plants through a process referred to as winter sowing. Winter sowing is a cost effective, low maintenance method of starting seeds in the winter for spring transplant. It is also a wonderful method, for those who have limited space, to start plants indoors since the containers are kept outdoors.
Many annual and perennial seeds require a cold period to germinate, a process referred to as hardening. In late summer, these seeds fall to the ground. During autumn, they slowly get covered with leaves and other materials. They then remain in the soil over the winter. Exposure to cold temperatures and moist conditions breaks dormancy and the seeds germinate when temperatures increase in the spring. Winter sowing replicates nature’s process in a controlled environment.
A wide variety of plants can be started using winter sowing. These include native plants such as milkweed, purple coneflowers, liatris, penstemon, Black-eyed Susans and perennial plants such as dianthus and phlox. You can also plant cool season annuals, cool season vegetables and a variety of herbs.
Creating Your Miniature Greenhouse
Plastic containers such as gallon milk jugs or plastic food containers can be used to create a miniature greenhouse that will reside outdoors and act as a house for your plants until they are ready to place in the outdoor gardens. They should have transparent lids so that sunlight can shine through and an opening that will allow rain and snow to reach the soil and the seeds it contains. Ideally the whole container should be transparent.
The “greenhouse” needs to be deep enough to hold 2-3 inches of soil and tall enough to allow for a few inches of headspace so the seedlings have plenty of room to grow. Before planting, thoroughly clean the container.
If using a milk jug, discard the cap. Cut around 3/4 of the jug just below the handle so you can fold back the top portion of the jug to plant and make several holes in the bottom of the jug to allow extra moisture to drain. After planting, reposition the top portion of the jug and secure it with duct tape.
If using a food container or other plastic container cut holes in the top to allow snow to reach the soil when it’s placed outdoors and cut holes in the bottom for drainage.
Fill your container of choice with 2 - 4 inches of potting soil, not gardening soil. Moisten the soil and allow to drain.
Sow seeds on the surface of the soil or a depth prescribed for the specific plant. Cover the seeds laid on the surface with a layer of soil and gently pat down.
Perennials and hardy annuals seeds require a consistent period of moist, cold temperatures before germination occurs in spring. So, these should be planted in January or February in Minnesota. Tender plants including annuals and vegetables can be sown later in spring (March or April) as they do not require a cold period in order to germinate.
Place the container outdoors where it will be protected from strong winds but where snow can reach it. The seeds require the moisture from the rain and snow. They should experience all the weather conditions they would in nature. Forget about your containers until the spring when the seedlings begin to grow and put out shoots. Once these seedlings emerge, monitor often. Even during the cold temperatures, the inside of the milk jug can heat up quickly and cause seedlings to wilt. If this happens, you may need to leave the container opened during the day but closed in the evening. Once temperatures warm up in spring, the top can be removed during the day and then put back on at night.
Transplant your seedlings to the outdoor garden when the soil reaches appropriate temperatures for the specific plants you have grown.
Have fun winter gardening in Minnesota!
Winter Seed Sowing, https://extension.illinois.edu/news-releases/winter-seed-sowing
Youth Gardening Activities Series, Winter Sowing Seeds, https://extension.missouri.edu/publications/ym105
Staring Seeds in Winter, https://extension.psu.edu/starting-seeds-in-winter
Photo credits: Lori Voll-Wallace, Penn State Extension (2), Illinois Extension (1)