Some seeds will need pre-chilling for better germination results. Here are some specifics on that process.
An earlier column gave specific instructions on how this can be done indoors in the refrigerator.
Many perennial seeds will need about four weeks of chilling.On the other hand, others will benefit from longer periods, 4-6 weeks.
In a pinch, I have given lavenders and columbines as little as 7-10 days, and still received uniformly high germination.
Some of the more commonly grown plants requiring stratification include purple coneflower, iris, daylily, perennial lobelias, clematis, many wildflowers, and some bulbs, such as lilies, Turks cap lily, and anemones.
Most seeds of deciduous woody species will generally need a lengthy chilling period before they will germinate.
Dogwood is an example, and there are many others as well, including redbuds and trumpet vine.
During the chilling period, examine the refrigerated seeds once or twice to be sure they aren’t sprouting. Should this occur, plant them immediately. This happened to me several times when I chilled Japanese maple seeds on a screened porch. Surprisingly, the sprouted seeds survived to become thriving plants, which I distributed free at a beekeepers’ meeting.
Regarding specifics as to which seeds require stratification and for how long, the Thompson & Morgan catalog notes if and when a variety needs chilling, and the specific amount of time recommended.
For more details, please refer to enclose a copy of the Thompson and Morgan instruction pamphlet, “The Germination Times Booklet.” A copy of this booklet is included with each order.
The catalog of J.L. Hudson lists the number of days for chilling as well as any other special seed treatments required, such as nicking.
If you choose to chill your perennial and woody plant seeds outdoors or in the refrigerator, you will be rewarded with more uniform sprouting and higher germination rates.