What Seeds Need Cold Treatment?
Seeds are the embryos of new plant life. Mimicking the the conditions in which seeds would germinate in nature is often necessary to maximize seed germination and grow new plants in a home garden or nursery. Cold stratification, or chilling the seeds, usually in moist sand or peat moss, is one of the most common treatments to break seed dormancy and encourage germination, as it replicates conditions seeds would endure through winter before sprouting.
Most tree seeds, as well as the seeds of woody shrubs, require cold treatment before they will germinate. According to the North Carolina Cooperative Extension, Redbud, Dogwood, Crabapple, and Southern Magnolia tree seeds all require cold stratification for several months to break seed dormancy and encourage the seeds to germinate, while Red Oak acorns, Southern Wax Myrtle, and Southern Sugar Maple require cold treatment for one to two months. The North Carolina Extension advises that cold stratification will speed germination of pine seeds as well.
According to the University of Kentucky Department of Horticulture, seeds of some types of herbaceous plants which grow in temperate zones require cold stratification before germination, which is best accomplished by placing the seeds in damp sand in a container in the refrigerator for one to three months. Among the flowering perennials commonly grown by home gardeners are the Aconitum or monkshood species, Gentiana or the many varieties of the gentian family, and Echinacea, including the ubiquitous purple coneflower as well as the many recent cultivars of this popular rayed garden perennial.
Mary Baldwin College's guide to Gardening With Wildflowers suggests gathering seed as a ecologically sound method of collecting wildflowers for growing in the home landscape. Many wildflower seeds must experience the false winter conditions of cold stratification before they will germinate. Columbine, Bleeding Hearts, False Solomon's Seal, Bloodroot, and Jack in the Pulpit are among the wildflower seeds that will not germinate, or will do so only slowly, without several months of cold treatment.