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What is seed stratification?

If you’re someone who likes to save seeds from perennials, to start the following year, then you may be familiar with the need for some seeds to undergo a cold period before they can germinate. This is a natural process that happens when a perennial goes to seed, drops seed, that seed is snowed over, and germinates the following years. The cold shock is what ensures vitality for the seeds that need it. This natural process is interrupted a bit if you save seeds from your perennials, storing the seeds indoors overwinter. However, you can mimic the natural stratification process yourself, making sure that you get good germination yields in the spring.

In a guide provided by the University of Washington, you have the option to try refrigerated stratification, outdoor stratification, or outdoor planting:

Refrigerated Stratification

  • Stratification is accomplished by placing seeds in moist planting medium in a cold environment for a period of time (two weeks to three months). Seeds require moisture, cold and oxygen. In general, this period of time allows an undeveloped embryo to mature.

Outdoor Stratification

  • Seeds may be kept outdoors through the winter in lined pits or raised beds. They must be protected from freezing, drying and rodent predation (use wire netting in the soil). Pits or beds are layered with clean sand, medium with seeds, more clean sand, etc.

Outdoor Planting

  • Some categories of seeds may simply be planted outdoors in the fall and natural stratification is allowed to happen.

If you have seeds saved from last year’s perennial plants, then it may be worth looking into if they need a stratification period to bring them out of dormancy, ready for spring and summertime blooms. You may only need to plant your seeds outdoors during the cold months, or at most, leave the seeds in your refrigerator until it starts to get warm outside. However you end up planting your saved seeds, take some joy in the fact that you’re helping the natural cycle of perennial plants and possibly getting some free plants along the way.

Whispering Hills Garden and Landscape Center is a full service landscape center and nursery located in Cary, Illinois. Stop in today to schedule a Spring 2022 cleanup. (Updated: 1/17/22)

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