Garden seeds: How old is too old?

QUESTION: How long do seeds last? If a seed packet says “purchase by 12/11,” would the seeds still be good for this year?  I’m looking at sunflowers, green beans, and other summer vegetables.

Packed for 2011. Still good? Probably, if they’ve been kept dry and cool.

It’s probably a common experience among gardeners to find packets of last year’s seeds – or seeds from two or more years ago (opened or unopened) stashed in a forgotten corner. They look too good to throw away, but is it worth wasting time and space in the garden to plant them if they may not germinate?

The good news is that many seeds last beyond the “sell-by” or “packaged for” date that’s printed on the packet, especially if they’ve been kept in favorable conditions – dry and reasonably cool. Seeds of parsnips, onions and leeks are among those that will only be good for a year, but seeds of most of the common garden vegetables can last two, three, or some, even five years. Here’s a short list from vegetable researchers atOregonStateUniversity:

Two years: sweet corn, lettuce, parsley, peppers, chard.

Three years: Bush and pole beans, carrots, cucumbers, melons, peas, squashes, tomatoes.

Four years: radishes, turnips.

Seeds of annual flowers are generally good for 1 – 3 years, the researchers say; seeds of perennials can last 2 – 4 years.

You can test the viability of a packet of seeds by placing a few in a moist paper towel in a warm room for a few days to see if they germinate. Seed Savers Exchange provides detailed instructions here.

If you have seeds left at the end of the season, the best way to store them is in a sealed jar with something to absorb moisture (rice or powdered milk are two suggestions). Store the jar in the refrigerator or a cool area in the house, such as a basement.