I love trying different edible plants and so I grow a wide variety of crops (and often several varieties of each one) every year. This adds greatly to my enjoyment of the garden, but also means that I end up with a lot of half empty seed packets at the end of the growing season. Fortunately most seed remains viable for at least 3 years (even if just sitting in a drawer) so you can use up the rest of the packet later. A few kinds of seed (corn, onion, leek, chives and parsnip) are only considered dependable for 2 years, so you should try and use these up in the following year. Others (cabbage, chicory, endive, cucumber, squash and tomato) may last as long as 6 to 8 years.
Seeds are sleeping plants
The exact length of time a seed will remain viable is determined by how it is stored. Seeds may not look like living plants but they are (just in a different form) and have to respire to maintain life processes. While a seed is dormant they do this at a very slow rate, but warmth and moisture (the same things required for germination) increase this rate, causing them to use up their food reserves more quickly. As these are gradually depleted, less is available for germination and their vigor declines until the seed is no longer able to germinate (this is why 5 year old seed isn’t as vigorous as one year old seed).
How to store seeds
If you are planning to use the rest of the seed in the following year, all you need to do is keep them in a dry, cool place. If you want them to survive as long as possible you must keep them very dry and very cool. This means drying them thoroughly (put them in a glass jar with a moisture absorbent such as silica gel) and then keeping them in a place that remains cool even in summer. For longest possible storage they may be kept in a freezer, though any seed you store in this way must be very dry, otherwise moisture in the seed may freeze and damage it.
Garden centers often sell off year old seed packets cheaply when the new seed arrives in February or March and this can be a good way to save a little money and try some new varieties. It should still be good for at least another year and often a lot longer (just be aware of which seeds are long lived and which aren’t). The best deal is seed that comes in packets lined with aluminum foil, as this keeps the seed very dry and extends its life considerably (I’ve had good germination from 12 year old lettuce packed in foil).
We make it easy
If you’re at all unsure how long you should keep your seeds, we include seed viability information right in the plant description.