Have you ever bought a packet of special seeds, maybe something a little unusual or more expensive than you’d normally buy, only to plant them and find that not one seed germinated?
Some seeds, especially those of prairie plants, woody perennials and trees and shrubs, need help in breaking dormancy before they germinate. This characteristic, called “innate dormancy” helps insure their survival in nature. The seeds know to wait out the winter or a dry season before sprouting. And if their pre-germination requirements aren’t met, they just won’t germinate.
For some seeds, this means exposure to cold, also called stratification. This is most easily accomplished in the refrigerator. Mix the seeds with an equal volume of moist, clean sand, vermiculite or sawdust and place them in a sealed plastic bag. The mixing medium should be barely wet as too much moisture will cause the seed to rot. Most seeds need three to four weeks of refrigeration, but some need much longer. A reputable seed company will have this information on the seed packet. If you’ve collected the seeds yourself, some internet or library research will be necessary to determine stratification time. Count backward on the calendar and start the cooling period so that it ends when you are ready to plant.
Another option is to plant the seeds in fall and let winter do the stratification for you. This may work, but realize that your valuable seeds may be subject to extreme temperature fluctuations, excessive wet or dry conditions, and damage by birds, rodents or other animals. Also, note that some seeds, lilacs and arborvitae for example, are double dormant and require a period of cold stratification followed by a period of warm, moist stratification, so if planted outdoors, they may take a year or more to germinate.
Other seeds, like morning glory, sweet pea, okra and others have very hard seed coats that inhibit water absorption. They need something to help soften or break the seed coat before they can germinate. This is called scarification. In nature, freezing temperatures or soil microbes soften the seed coat in winter. Scarification can also occur as seeds pass through the digestive tracts of animals.
There are several methods home gardeners can use to scarify seed coats. Large seeds can be nicked with a sharp knife or cut with a razor blade. Be careful not to damage the embryo inside the seed. Medium and small seeds can be rubbed between two sheets of sandpaper. To scarify large numbers of seeds quickly, slip a sheet of coarse grit sandpaper inside a jar, add the seeds, screw on the lid and shake the jar until the seed coat wears down. The seed coats will look dull when they are sufficiently scarified.
Even seeds with thin seed coats can be helped along. Soaking large seeds like peas, beans or nasturtiums in lukewarm water for several hours before planting will speed germination.
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