Vegetable seed viability depends on various factors.
Seeds that gardeners plant in home gardens, community gardens, fields and farms are living structures waiting for the right conditions to begin a new growth phase. Viability refers to the seed's ability to sprout and begin leaf and root growth. Seeds have variable life spans dependent on many factors, and they can die. If not properly stored to preserve their inner embryos and kept safe from attack by fungi and bacteria, seeds quickly dry out or are killed by invading organisms.
Ideal Storage Conditions
A lot of seed viability depends on how it's stored. Ideal seed storage conditions to preserve and maintain viability are cool, dark and dry environments. Temperatures between 40 and 45 degrees Fahrenheit and humidity between 45 and 50 percent are best for seed storage. Sealed glass or plastic containers stored in a closet are good seed storage conditions. Seeds should be dry, with no green or moisture, before being sealed for storage or they will mildew. Thick plastic zippered bags also make good storage containers. Keep seed containers out of strong sunlight.
What Kills Seeds
High temperatures and high humidity are the two main factors in seed death. Seeds exposed to direct sunlight or left in high moisture conditions die or become severely compromised. Although you want to avoid fungus and bacteria from moisture, total dehydration of the seed kills it. Sealed glass keeps the embryo's moisture even without exposing it to extra moisture and organisms. Time kills seeds also. Although some seeds stored in ideal conditions can remain viable for up to 10 years, too much time from seed formation to planting results in worthless seeds that won't grow.
Seed Storing Tips
Let freshly collected seeds dry outside on a windless day. Use dry paper towels or a screen to lay seeds out on a flat surface, not overlapping or piled together. Wash seeds from wet fruit such as tomatoes and cucumbers, using a fine mesh strainer to remove as much liquid and fruit pulp as possible for drying. Once seeds are thoroughly dried, place them in glass containers marked with the type of seed and the date.
Common Vegetable Seed Viability
Common vegetable seeds that remain viable for up to four years include beet, cabbage, Swiss chard, eggplant, squash, pumpkin and tomato. Vegetables with a brief viability of one year include lettuce, onion and parsley. Vegetable seeds that last a few years include beans, carrots, peas, spinach and okra. Seeds may still sprout after these time frames, but in lower percentages than fresher seed, and plants won't be as vigorous.
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