Sleeping Seeds?

A Little Bit More

Don’t get the impression that ALL seeds need a dormant period, they don’t. But most of the seeds from native plants in the colder regions of the world do. The term “stratification” probably sounds strange for this process; I know it did when I first heard it. This term comes from the horticultural practice of layering (or stratifying) multiple levels of seeds in peat moss or moist sand and exposing them to cold temperatures to simulate natural conditions needed to initiate germination.

American Beech seed sprouting

In most wild plants, seeds contain an inhibiting hormone called abscisic (ab-SISS-ic) acid that prevents a seed from germination. Over time and at an optimal temperature of about 4ºC (39ºF) enzymes within the seed are able to breakdown this inhibiting chemical and prepare the seed for the germination process to take place. As you can guess, abscisic acid prevents seeds from germinating in the fall, just before cold temperatures arrive that would otherwise prevent normal growth of a delicate, young plant.

Once the stratification process is complete, however, a seed doesn’t automatically germinate; it must now wait for the proper temperature and moisture. Once all of these parameters are met, and this almost always occurs in spring, the seed sprouts and begins growth.

Activities

Science – Stratification

Objectives: Experience the process of stratification firsthand

Materials: Seeds, plastic zip-lock bags, peat moss or sand (optional), access to refrigerator

Although some of the literature states that stratification can take place within 4 weeks at 4ºC, it will probably prove best to exceed this minimal time period. Refrigerators are often not as cold as 4ºC (39ºF) – optimal stratification temp - so the time your seeds need to be dormant will be longer. To be on the safe side, I’d keep my seeds at least 6-8 weeks in the refrigerator before planting.

  1. In the fall, you can have students bring in seeds they find in their yards, along the streets, or from local parks and woods. Those you might want to try can include apple seeds, walnuts, hickory nuts, acorns, goldenrod seeds, aster seeds, berries from shrubs and a whole assortment of other species. You’re collecting FALL seeds, not spring seeds, because spring seeds don’t need this process to germinate! If you can obtain some seeds that are outside during the winter, you won’t need to stratify these if they’ve experienced at least 4-6 weeks of cold, since they’ve already been prepared “naturally” for germination.
  2. Once you’ve accumulated your seeds place them in zip-lock plastic bags with just a wee bit of moisture (moist sand, peat moss, or a few flicks of water) and seal tightly.
  3. Label your seeds if you know what kind they are and also date the time of the placement in the refrigerator on the package. Also, make a note on your calendar for “X” number of weeks into the future that “it’s time to remove the seeds and plant them”
  4. Place your seeds in the coldest part of the refrigerator and forget until your calendar prompts you to retrieve them. CAUTION – don’t get the idea that you can speed this process by keeping the seeds extra cold. Stratification takes place most rapidly at 4ºC – not above nor below that temperature!
  5. Once the 6-8 weeks are up, take the seeds out of their containers and plant as you normally would any seeds. Place in a warm area of the room, keep moist (not wet) and watch what happens.

Don’t expect 100% germination. Even in nature not all seeds survive to germinate but what does sprout will be fun and educational to watch as it grows. Once you have seeds sprouting you may want to decide where it will be best to plant outside if you choose not to grow them in your room. If you do choose to keep your seeds in the room, be sure you have plenty of space for their growth and realize that if you have plants that live for more than one year (perennials) you’ll need to allow them to be dormant once winter arrives.

Key Concepts

Structures and Functions, Life Cycles, Growth and Development

Questions

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Filed under: Plants