Seeds that require “stratification” (or cold treatment) to germinate are best for this method, which gives seedlings an earlier start. Master gardener Jennifer Behm gets an 80 percent germination rate with native plants–butterfly weed, hyssop, blue vervain, big blue stem grass, coneflowers, rudbeckia–which she starts in December or January.
1. Wash an empty plastic gallon milk jug container with hot soapy water.
2. Cut slits in the bottom for drainage.
3. Cut all the way around the milk jug, making sure the bottom is at least 4 inches tall. Fill the bottom with potting soil to about 1 inch from the top, plant seeds to appropriate depth, water well and let drain.
4. Put top half of jug back on with duct tape. Leave the small cap off; the hole will let snow and ice melt into the plant.
5. Label your container and set it outside where it won’t be blown away. Mother Nature’s freezes and thaws will be just right for the seeds to germinate.
6. Once the snow melts, water seeds when soil dries out (which can be daily once the weather warms up). The soil in the jug warms up much faster than the soil in the ground, and the seedlings emerge much earlier than anything in the garden. The milk jug acts like a miniature greenhouse, warming up by day and protecting the seedlings from frost at night.
(If it doesn’t snow where you live, consult www.wintersown.org for stratification instructions.)
7. When the seedlings get ½-inch high, take the lid off completely.
8. Once the seedlings are 1 to 2 inches tall, transplant into the garden.