The Effect of Dormancy on the Quality of Vegetable Seeds
Dormancy refers to the period of time between the production of seed by a plant and when the conditions become right for the seed to sprout, or germinate. During dormancy, the biochemical activity of the plant embryo inside the seed slows down. Plants vary in how long a seed may lie dormant while still remaining viable. Some seeds, such as parsnips, must germinate within a year of production, while others, such as muskmelon, may still germinate after five years. In other cases, seeds hundreds of years old found in archeological digs still sprout under the right conditions. Storage conditions also determine whether a dormant seed will germinate. Does this Spark an idea?
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A Normal Process
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A dormant seed is not necessarily a low-quality seed. Dormancy is a normal process used by seeds to protect the embryo within the seed until conditions are optimal for growing. As the Centre for Genetic Resources in the Netherlands points out, seeds without dormancy may fail because the seeds germinate too soon, before conditions are optimal, causing the plant to die.
Seed Quality over Time
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The longer a seed lies dormant, the less likely that it will properly germinate when planted. The Colorado State University Extension recommends planting seed the year after it is produced whenever possible, as the germination percentage will decline each year after. Test older seeds annually for viability.
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Planting Dormant Seeds
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Vegetable seeds usually germinate without extra help from you. If the soil temperature is right for the vegetable that you are planting, the seed should germinate on its own. Planting seeds at the correct depth is essential, and this is a major reason why otherwise healthy seed will not germinate. Plant according to instructions on the seed packet, or plant at a depth twice the diameter of the seed. When in doubt, plant shallower, especially for hard or clay soils. Extra soil can be added once the plant germinates, if needed. Also be sure that the seeds have enough water, but not so much to make the ground swampy.
Breaking Dormancy
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Some seeds need extra help to break dormancy. Some seeds require exposure to light in order to begin germinating. Other seeds with unusually hard coats, such as okra, require scarification, or a slight cutting or breaking of the seed coating, in order to acquire enough water to break dormancy.
Testing Seeds
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If you have vegetable seeds more than one year old, test them for germination before using them. The Washington State University Extension Office recommends testing for germination by placing ten seeds on top of a damp paper towel and sealing them inside of a plastic bag. Keep the seeds at room temperature for about a week. Parsley, carrot and celery will take longer. Count the seeds that germinate. If 80 percent or more germinate, the seed is still good. If 50 percent to 80 percent germinate, you will need to sow the seeds more thickly. If fewer than 50 percent germinate, the seed is no longer good and should be discarded.
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References
- "Rodale's Ultimate Encyclopedia of Organic Gardening"; Fern Marshall Bradley, Barbara W. Ellis and Ellen Phillips, editors; 2009
- Washington State University: Seed Germination
- Centre for Genetic Resources: Seed Quality in Genetic Resources Conservation
- Colorado State University Extension: Saving Seed
Resources
- Photo Credit vegetable image by dinostock from Fotolia.com
