For some seeds, all that is needed to germinate is warmth and moisture. However, for others, germination only takes place once the seeds have experienced the appropriate number of cold/warm cycles. It’s similar to fruiting trees and berries – a specific number of “chill hours” is needed in order to set the fruit.

With seeds, stratification provides an approximation to what the seed would experience in the natural world. By alternately cooling and warming seeds, and ensuring they are seated in a good growing environment, you can trick them into germinating. In most cases, stratification is a better fit for perennials rather than annuals, though.

In order to stratify seeds, you will need to place them in an appropriate rooting material. This could be peat, or it could be something as simple as a moistened paper towel. For cold stratification (seeds requiring chill hours), you’ll need to store them and their growing material in a cool place, generally refrigerator temperature. For seeds that require warm stratification, you would store them somewhere with a temperature between 68 and 85 degrees F (the average room temperature in your home may be perfect).

Check your seeds regularly for signs of activity. The length of time they need to spend in stratification will vary greatly depending on the type of seed in question. Note that there are some seeds that need both stratification and scarification, such as Baptisia. Scarification is the process of cracking a hard, outer coating to allow the seed to germinate