by Katie Parker
Have you ever planted seeds, but nothing sprouted? This could be the result of many different things such as soil moisture, seed viability, soil temperature, planting depth, and many other factors; however, not all seeds are ready to sprout as soon as they are planted in soil.
Some seeds require a temperature change to trigger the end of a dormancy (or sleep) period; this process is called stratification.
Stratification occurs naturally when seeds are sown outdoors through the cold winter. It is a survival mechanism, making it so the seed does not prematurely germinate.
However, if you’re like me and failed to get your seeds planted this last fall, we can still grow them this spring by mimicking the required conditions indoors. To stratify seeds indoors, place them in a moistened paper towel, sand, peat or vermiculite within a closed container or sealed plastic bag.
The stratification process can require cold or heat. For cold stratification, put the container in the refrigerator (33-40 F); for warm stratification, store the container where the temperature is between 68 and 85 F. After removing the seed from the refrigerator, it can be sown into pots or direct seeded outside if conditions are suitable for growing outdoors.
The length of time needed to stratify is dependent on the plant species; this period typically varies from one to three months. It is important to check your seeds occasionally to make sure there is still some moisture in the container but not too much which can cause mold. You can also check the seeds periodically to see if they are sprouting; sprouted seeds can be planted.
Many plants require a period of cold temperatures to break their dormancy cycle with woody plants and herbaceous perennials being some of the more common species.
Some popular plants that require stratification include many of the milkweed species, purple coneflower, false indigo, black-eyed Susan, flowering dogwood, redbud and many others. Many times, seed packets will let us know if there is a cold period requirement for germination, but it is always a good idea to research any germination needs — especially when it comes to collecting and saving seeds.
Good Growing Tip: Don’t wait too long to start seeds that require a cold period. Depending on the required period of stratification, it can add one to three months when starting seeds.
