Many of our Wyoming native plants require cold stratification for germination of seed. “Cold stratificaton” is a fancy term for “needs some time spent in cold dirt.” It’s easy to understand. If a northern plant naturally distributes its seeds in the autumn, those seeds will spend the winter being subjected to cold and rain and snow, and even intermittent periods of dry cold.
I have reproduced this environment for seeds by placing flats of planted seeds in freezers and refrigerators, and I have had pretty good success. But this year I am doing it the old fashioned way, by placing my flats outside under some large shade trees and covering them with a thin layer of leaves. It’s easy, low labor, and works great for the native plants who self sow here.
Today I sowed some of my favorite native Wyoming plants for my landscaping efforts in 2011: Eriogonum umbellatum, Antennari, Amelanchier alnifolia, Ceanothus velutinus, Epilobium angustifolium, and Penstemon angustifolius.
In the past, I have planted Antennaria in the early spring with good germination rates, but the seeds are so fine and difficult to prevent from washing away. So this year I am going to sow them now in a flat, let them germinate where I can keep track of them, then move them in clumps into the garden.