Seed catalogs seem to come in the mail to entice us gardeners just when we start to feel the drag of winter. Garden seed can be expensive, and this is why many gardeners consider using leftover seed purchased from previous years. Many wonder how long they can expect their old seed to be usable when planning for a new season of gardening. January is a good time to evaluate old seed or do a germination test to determine if new seed should be purchased.
Impacts of storage
The way seed is stored is perhaps the biggest factor that will impact its longevity. Seed stores best if kept in a cool, dark, dry location that is ideally less than 50 degrees. A zip-locked plastic bag or a plastic jar with a rubber seal such as a canning jar works well to provide an air and watertight environment.
When seed is completely dry, a freezer is the best way to store it for the long term. Seed that has 8% or less moisture can be frozen without harm and will actually store much longer than seed stored above freezing. Seeds dried to 8% or less moisture will break instead of bending when folded. Those that have a hard seed coat such as corn and beans will shatter rather than mashing when struck with a hammer. If you are interested in saving and drying your own seeds, an excellent reference on effective procedures is given in the book “Seed to Seed” by Suzanne Ashworth.
Length of seed life
Crop groups vary in seed longevity. Use the following as a general guide for seeds stored under cool, dry conditions. Crucifers (cabbage, cauliflower, broccoli): 4 to 5 years, corn: 2 to 3 years, lettuce: 3 to 4 years, spinach, beets, carrots and chard: 2 to 3 years, cucurbits: squash, melons (including watermelon): 4 to 5 years, tomatoes: 4 years, peppers: 2 years, onion, parsley, parsnip and salsify: 1 year.
If you are unsure of viability and have plenty of seed, there is an easy method of determining how good your seed is. Place 10 seeds on a paper towel moistened with warm water and cover with a second moistened towel. Roll up the towels and place inside a plastic bag with enough holes for air exchange but not so many that the towels dry quickly. Place the bag in a warm place such as the top of a refrigerator. Re-moisten the towels with warm water as needed. After the first week, check for germination. Remove sprouted seed and check again after another week. Add these numbers together to determine the percent germination for the seed in question. If the germination rate is low, it is time to purchase new seeds.