A primer on native seed stratification
Story and photos by Jeanne McRight
Native seeds have particular germination needs that relate to the habitats they evolved with. Compared to domesticated plant species, native plants take much longer to germinate, or begin the growing process. Many native seeds live for years in soil seed banks before the perfect conditions arrive for germination - in order to speed up germination, we can simulate these environmental patterns.
Some species need to be cold stratified, meaning the seed needs to be kept cold and moist for a period of time before they will germinate. The cold temperature mimics winter conditions that the seed would normally experience in nature. It is important to research the species-specific needs before attempting germination. That chart provided by NANPS is useful for this purpose and it is linked below.
See these tips below for germinating your native seeds, and have fun!
Stratifying seeds indoors
Native forb (herbaceous flowering plant) seed is often germinated indoors in trays or pots under lights where ideal germination conditions can be simulated. Below are some of the methods you may need to employ to get your native seeds to germinate:
Above: Mohan cold-moist stratifying swamp milkweed seeds.
Cold-Moist Stratification (Physiological Dormancy): Natural enzymes in some native seeds prevent them germinating until winter has passed. This ensures that the seed germinates in the spring at the beginning of the growing season, as opposed to germinating in the fall before the freezing, killing temperatures of winter arrive. It is easy to simulate a short winter by first sprinkling seeds thinly across a moistened coffee filter or smooth paper towel, making sure it is not dripping wet. Then fold the filter and place it in a ziplock bag in the refrigerator for 60 to 90 days.
Above: Showy Tick Trefoil (Desmodium canadense) undergoing scarification and stratification.
Scarification (Physical Dormancy): Seeds with very tough exteriors must have their seed coat broken before water can reach the inner tissues. The seed coat can be clipped, pierced with a knife, or scratched with sandpaper. After treating the seed, follow 60 days of the cold-moist process described above.
Complex Germination (Double dormancy): Some species' seeds require alternating periods of cold and warm to germinate. In nature that can mean seeds germinate in their second year.
Stratifying seeds outdoors: Over-wintering
An even easier method for germinating seeds is to over-winter seeds outdoors. Native plants are accustomed to local climatic conditions and do not need to germinate indoors, in greenhouse-like conditions. Therefore, another option is to plant the seeds in the fall in containers, using the steps outlined above, and leave them outside where they will receive precipitation and cold conditions throughout the winter. They will naturally germinate in the spring once soil temperature increases. It will be necessary to protect your seeded pots from squirrels or birds that may dig in the pots, and possibly from extreme winter winds. Hardware cloth or chicken wire can be laid flat and weighed down with heavy objects over the seeded pots as protection
Indoor Native Seed Stratification. North American Native Plant Society https://nanps.org/96358-2/
Cullina, W., (2000) The New England Wild Flower Society Guide to Growing and Propagating Wildflowers of the United States and Canada. The New England Wild Flower Society.
Toogood, A. (Ed.). (1999) The American Horticultural Society Plant Propagation. DK Publishing.