As the new seed catalogs arrive in the mail in January, it is a good time to take stock of leftover seed before you place an order. Carry-over seed can and should be used before its viability declines, especially given the cost of buying new seed each year. As you go through older supplies, evaluate what crop seeds you have on hand, how much is leftover and is it enough for next year? Try to determine age of seed by packing dates on the package, and consider conducting germination tests.
Always keep in mind that a seed is alive and respiring, but very slowly in a resting or dormant state. Viability of stored seed is affected by two main factors: seed moisture and storage temperature exposure over time. These factors interact with natural seed longevity, which varies greatly between species. Thus when evaluating aging seed stock, how and where you kept your seeds are important considerations, as well as knowing the natural seed life expectancy.
The combination of high seed moisture and either high or low storage temperature regimes are especially detrimental to seed longevity. Low seed moisture means longer life, particularly when it is exposed to fluctuating temperatures. Silica gel and calcium chloride are good mediums to dry seed and also control humidity in a damp storage environment. It is important not to allow direct seed contact with these materials. Cool, consistent, basement or refrigerator storage is preferable to attic or outdoor garden shed storage. Periods of high temperature exposure, such as a seed packet left in direct sun or in a hot shed, can significantly reduce seed longevity or kill it outright. For many species, sub-freezing temperatures can be detrimental. Ideal seed storage temperatures are between 40 to 50 degrees F, with desirable seed moisture for most crops around 10 to12 percent. Lower moisture of 5 to 6 percent is better for long term storage in airtight containers, with the exception of okra and bean seed which can develop hard seed coats and not germinate well if kept below 10 percent moisture.
Relative life expectancy under favorable storage conditions for certain crop groups is, in years: legumes (beans) 3 to 4 yrs; crucifers (broccoli, cauliflower) 4 to 5 yrs; corn 2 to 3 yrs; lettuce, endive and chicory 4 to 5 yrs; spinach, beets, carrots and chard 2 to 3 yrs; cucurbits (melons, squash) 4 to 5 yrs; tomatoes 4 yrs; peppers 2 yrs; onion, parsley, parsnip and salsify 1 yr. As seed gets older, the percent germination declines at varying rates depending on conditions and species.
Seed packages state percent germination on the package as well as the year that the lot was packed. New seed usually tests between 85 to 99 percent germination. As noted, even under ideal storage conditions, germination of any seed lot declines with time, as well as the vigor and rate of germination, so it is best to test percent seed viability if you have doubts. This can easily be done by wrapping some seeds in a wet paper towel, keeping them moist and warm (65 to 70F) over a period of 3 to 7 days and counting germinated seeds. If the percentage is low or germination is slow or variable, it is best to discard the lot. A weakened seed, even though it germinates, makes for a weak seedling and poor early growth.
Properly storing and utilizing older seed is a great way to save on garden seed costs, though it should always be evaluated before planting. A poor stand in the garden results in lost growing time if it needs replanting, and often a planting delay beyond the ideal window of time. For more information on vegetable gardening, check out the University of Illinois publication "Vegetable Gardening in the Midwest", available from your local county Extension office or visit the new U of I Extension website "Illinois Vegetable Garden Guide" at http://web.extension.uiuc.edu/vegguide/.
Source: Anthony Bratsch, Extension Educator, Horticulture (Serving East-Central and Southeastern Illinois), firstname.lastname@example.org
Pull date: March 30, 2009