Sowing Seeds in Winter

Winter sowing is a method for growing native plants that involves planting seeds outdoors in containers during the winter. It mimics the natural process of stratification, where seeds experience the cold and precipitation of winter, followed by warmer temperatures in spring. This process is critical for breaking dormancy in many species, especially wildflowers and sedges.This process is called cold stratification. Nature does it, well, naturally. People can recreate this in controlled conditions.

I consider myself to be a pretty good gardener - not a master - but I'm new to cold stratification. That probably explains why some seeds that I planted in early spring never sprouted. 

Native plants give food and shelter to bugs and birds, and don't need much to thrive. They stay dormant over the winter, then germinate at the right time in the spring. 

Mixing seeds with barely damp sand, vermiculite, or peat moss is the start. Some people put this damp seed mixture in a container in the refrigerator, but I was told by some other wiser gardeners that it's better to let nature do the job.

The seeds of some species go into a period of embryonic dormancy and often will not sprout, or will have a poor germination percentage, until this dormancy is broken. Other species have seeds with a very hard seed coat, and exposure to the moist cold helps break down this shell for easier germination in spring. 

General Directions
Use containers with drainage holes that are about 3-4 inches tall and have a clear top with ventilation holes. I see that people cut old plastic milk jugs in half, sow seeds and reattched with duct tape. Leave the cap top open.
Cover seeds with a layer of sand to hold seeds in place from rain. Freezing and thawing will works the seeds down as it does with seeds that plants self-sow. I'm using a window screen over them in an old cold frame.

Getting this done before a snow is also recommended.

When they naturally sprout in spring, treat them as you would any seedlings. I worried that if they sprouted too early, they would die in a cold snap but others have told me that nature will take care. Still, I'll probably add some protection in early spring. Keep the seedlings watered throughout the growing season. Plant them directly into the ground or move them into regular containers.

What species should you winter sow? My first thought was milkweed which I planted last spring and had lousy results. You can find lists of species but here is a start: Asclepias, Aquilegia, Amsonia, Aruncus, Baptisia, Chelone, Echinacea, Eupatorium, Eutrochium, Geranium, Spicebush Mountain Laurel Coastal Pepperbush New England Aster White Wood Aster Zigzag Goldenrod New York Ironweed Eastern Bluestar Blue Lobelia Butterfly Weed Swamp Milkweed Common Milkweed Foxglove Beardtongue Wild Indigo. 

More at wildrootsnj.com/blog/sowing-native-seeds-in-winter