Do Seeds Expire and Go Bad?
Part of managing this year’s garden is thinking about next year’s seeds. You may be able to use leftover seeds from this year’s garden in next year’s plan. Or you might be able to save seeds from this year’s harvests. In very general terms, like other living things, seeds can become damaged or diseased and die. The rate at which they lose viability varies by seed type and, most important, storage conditions.
Viability Lore and Science
Legends assert that plants have grown from seeds found in ancient city ruins and royal tombs. Perhaps best known are accounts of lotus seeds found in a Manchurian lake bed, sprouted successfully after 1,200 or more years; in 2002, two Manchurian lotus seeds over 400 years old were grown into mature plants at Brookhaven National Laboratory. According to the U.S. Forest Service, more realistic estimates set the length of time most seeds can remain viable at approximately 150 years. The Kew Royal Botanical Gardens Millenium Seed Bank, a worldwide seed conservancy project, regularly tests many varieties of seeds for viability every five to 10 years. Past and ongoing studies of found seed stashes suggest that numerous members of the bean family (Leguminae; Fabaceae) and grass family (Graminae; Poaceae) may be viable after 40 to 70 years (see References 7, 8 and 9). Not surprisingly, a number of these are commonly regarded as weeds.
Estimating Garden Seed Viability
Scientists classify the lives of seeds as microbiotic, or less than three years; mesobiotic, from three to 15 years; and macrobiotic, 15 years or more, although many factors makes these categories only approximations. Most garden seeds fall into the first two categories; and seeds of plants consumed in their entirety as food, like onions, tend to be the most short-lived. Because of the critical importance of seeds as food sources, home gardeners will likely find more generally accepted information on vegetable seeds than on flowers. Oregon State University Extension, for example, offers only a general guideline for flower seeds, estimating a viability of a year or two for annuals and two to four years for perennial flowers.
Vegetable Seed Viability
A comparison of estimates from two seed producers and two university extensions divided vegetables roughly into three categories. Seeds regarded as viable for one to three years were beans, carrots, corn, leek, onion, parsnip, parsley, spinach, peas and peppers. Those viable for three to five years were beets, brassicas, celery, chard, eggplant, lettuce, cucumber, radish, squash and pumpkin. Generally, tomato, muskmelon and watermelon seeds were considered viable for five to 10 years.
Factors Affecting Viability
In some ways a seed needs to be treated like the plant it will become. Extreme temperatures and excessive moisture are equal threats to seeds. Excess moisture can produce mold or foster fungal diseases and rot in the seeds of most plants that grow in temperate zones (U.S. Department of Agriculture plant hardiness zones 3 through 9), while seeds of plants from subtropical and tropical climate zones (zones 10 and 11) may require high humidity to survive. Cool, dry, dark, clean conditions are necessary to store most temperate-climate seeds, whether purchased from commercial growers or collected from your garden. Keeping seeds in sealed containers prevents mold spores or other airborne organisms from infecting them. Some experienced seed-savers save refrigerator space for winter seed storage. For tropical or non-native plants, information from seed packets, grower sites and botanical gardens can help you provide variety-specific storage for seeds.
For successful seed saving, wait until seeds are fully mature before harvesting them. No matter how carefully stored, immature seeds lack the ability to become new plants. With vegetable seeds, for example, wait until vegetables are slightly past their prime; the seeds of a wrinkled pepper or overripe tomato are mature and ready for storage. Typical seed-packet directions include the length of the typical germination period, usually within 14 days for annuals, and often indicate a soil temperature desirable — and sometimes essential — for germination. Even perfectly viable seeds may not germinate with the wrong soil temperature, water or light. Seeds with very hard outer coverings may benefit from being scraped with a knife blade or sandpaper. Others need the artificial wintering known as cold-stratification, in which seeds spend weeks to months between layers of chilled moist soil or planting medium. Still others germinate faster after being soaked.Do Seeds Expire and Go Bad?. Part of managing this year’s garden is thinking about next year’s seeds. You may be able to use leftover seeds from this year’s garden in next year’s plan. Or you might be able to save seeds from this year’s harvests. In very general terms, like other living things, … ]]>