All vegetable seeds have a limited shelf life. This ranges from one year for plants like parsnips to up to 10 years for plants like tomatoes. Exactly what storage life a particular plant has can be looked up in reference books, or perhaps found on the Internet. Some examples of common plants are peppers (3 years), sweet corn (3 years), other corn (5-10 years), and so on.
Storage times for a particular variety of plant seed are very dependant on good storage practices, and as such few commercial suppliers of seeds will guarantee their products beyond the year in which they were sold to you. Because germination rates for seeds will only decline with their age, most seed companies as a matter of good business practice and with the intention of providing the highest quality product to their customers will only sell seeds from the most recent year’s harvest.
What happens if you try to grow old or improperly stored seeds? The quality of seeds is measured by their germination rate. Older or improperly stored seeds will have a lower rate of germination, or may not germinate at all. If you are unsure about the quality of some seeds, nothing will be lost by just trying to plant them and seeing what happens. If they grow, the plants will likely be just as healthy as plants grown from fresh seed. If you want to test some seed for the ability to germinate, just set them in a few layers of paper towels and keep moist and in a warm place for about a week.
The most important things to keep in mind when storing seeds are to keep them dry, at a steady temperature and out of direct sunlight. Beyond this, a cooler temperature is better than a warmer one.
A good choice of location to store seeds is the refrigerator. You must insure they stay dry, and this can be done by first putting the seeds in a plastic or glass container.
For very long term storage of seeds, one of the best containers is a glass jar with a rubber seal. This is because all plastic containers will leak a little bit over time.
For long term storage of seeds they can be frozen. Before freezing seeds, you must ensure they are dry enough or the water inside of them will expand during freezing and damage the seeds. A rule of thumb is if a seeds breaks when you bend it, it is dry enough, otherwise it is still too moist. Freezing seeds can increase their shelf life up to 10 times what would otherwise be possible, for example tomato seeds can be stored up to 100 years, peppers 30 years, and so on.
One of the most common ways of drying seeds for long term storage is to use silica gel. There is a special type of silica gel with a color indicator, that is very useful to seed savers. The most common type available in the US is blue when dry, and changes to light pink as it absorbs moisture. Because this type of silica gel contains small amounts of cobalt, which is poisonous and a potential environmental contaminate, there are also other types available. In Europe the most common types are orange changing to blue, or orange changing to colorless. Color indicating silica gel can be reused over and over, by drying it out in an oven at about 125C (250F) for several hours until it reverts back to its original color.
To dry seeds with silica gel, place them together with an equal amount by weight of silica gel in a closed container. Let it sit for 7 days. Beans and other legumes should not be over dried or they may be damaged, so you may wish to dry these for only 5 days. If you suspect you have over dried a particular batch of seeds, you may wish to germination test the seeds to make sue they will still grow.
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