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Seed Dormancy: Botanical "Hibernation"
By John Murgel, Horticulturist on Jan 10, 2012
While taking advantage of the warm daytime temperatures in recent weeks to get some pruning in, I was hailed from the pathway nearby.
"Do you ever worry about seeds coming up early during warm spells like this?"
In a word, "no." But why not?
The seeds of most temperate plants have evolved a variety of mechanisms to avoid arriving on the springtime stage ahead of cue. Together, these mechanisms are generally known as dormancy. Dormancy enables seeds to wait until conditions are favorable before germinating. Length and strength of dormancy varies among plant species, and is controlled by physiological and anatomical characteristics. Some dormancy can be very deep indeed--seeds of many plants can remain in the soil for decades before germinating.
Seed dormancy is often divided into three categories: innate, induced, and enforced. Innately dormant seeds cannot germinate when fresh, even if conditions seem perfect.—an adaptation to delay sprouting until the appropriate season. In temperate North America, winter temperatures can induce hormonal changes within the seed or simply damage thick seed coats to allow plant embryos to continue development. Many Colorado native perennials require a long period of cold before germinating. This prevents “accidental” germination during brief winter warm spells.
Induced dormancy affects seeds that could germinate at once but that have been dispersed in unfavorable conditions. One common form of induced dormancy is initiated when seeds are buried deeply, depriving them of needed oxygen. Immediately after ripening, such seeds will germinate readily in light or dark, but after being buried they undergo physiological changes that will only allow them to germinate in the light, an adaption to ensure that the seed is close enough to the soil surface to thrive after germination.
Enforced dormancy is the simplest form of dormancy—it occurs when a seed is deprived of any or all of its germination requirements (water, light, or a suitable temperature, for example). No special physiological adaptations are required for such dormancy, only the enforcement.
Seeds may exhibit any or all of the three dormancy types; all designed to give young plants the best shot at success.
I love seed dormancy because it helps brighten the cold, grey stretch between Christmas and Memorial Day. “But how?” you might ask…
“By letting me plant my garden in January!” I would reply. NOW is an excellent time to sow seed of native plants. Scattering seed throughout the yard is quick and painless, plus it comes with “Johnny-Appleseed” charm.
If you like a bit more control, you can sow native perennial seed in small pots, empty yogurt cups, trays or any other suitable container. Simply fill the pot with potting mix, add seeds, water, and place in a shady spot outdoors. I find the shade provided by my neighbor’s fence just about right, plus it’s close to the sidewalk so I can scoop extra snow over the pots to insulate them from the worst of winter’s cold. In the spring you will be rewarded as your very own miniature nursery fills with new garden plants!