Wednesday, April 13, 2016

Starting Those Hard to Grow Seeds: Stratification and Scarification By Brooke Colburn

Spring is creeping upon us here in the Front Range, and if you plan to start any of your flowering, perennial, native, or woody plants from seed, they may require some special treatment to overcome dormancy and germinate. There are two general types of seed dormancy: mechanical and chemical. Mechanical dormancy refers to a seed coat that is impermeable to water and or air, and it must be broken by a process called scarification. Chemical dormancy involves chemicals in the seed that must be leached away or broken down by a method called stratification.

Seeds with thick seed coats may require scarification to allow oxygen and water to pass through and trigger germination. This usually occurs in nature by weathering from the elements or from the seed passing through the digestive system of an animal. To scarify your seeds at home, use one of the methods described here:
  • Scrape the surface of the seed with sandpaper until the cotyledon can be seen
  • Cut the seed coat with a knife
  • Pour hot water (~200° F) over the seeds and allow to soak for 12-24 hours
Scarification is a technique required to germinate iris (Iris sp.), sweet pea (Lathryrus odoratus), nasturtium (Tropaeolum majus), and other seeds.
Larkspur seeds on moist paper towels for stratification
Stratification is a process that mimics winter and breaks down chemical dormancy. Most frequently, this involves a moist chilling process. Follow this procedure for most seeds requiring stratification:
  • Soak in water overnight
  • Place in moist sand or peat, either in a pot or directly in a plastic bag
  • Seal inside a plastic bag
  • Store in a refrigerator at 32-45° F for 60-90 days, or as required
Seeds requiring stratification include lupine (Lupinus perennis), columbine (Aquilegia sp.), clematis (Clematis sp.), larkspur (Delphinium sp.), purple coneflower (Echinacea purpurea), penstemon (Penstemon sp.), and many trees and shrubs.
Scarification and stratification are useful techniques when planting certain hard to grow species. For more specific details and requirements, refer to the resources below.
Starting Perennial Flowers from Seed Can Be a Challenge.