Above are some of the many packets of seeds I'm considering using for this year's demo garden. We received generous seed donations from High Mowing Seeds, Seed Savers Exchange, and Southern Exposure Seed Exchange. Baker Creek Heirloom Seeds also has a donation program, which we may apply to next year.*
It's an exciting time of year, not so much in the garden (although I was in mine on Monday, when it was 50 degrees out - seems like a distant memory now!) but inside the gardener's head, which is full of imaginings of spring, summer, and fall. If some of you are sketching your garden bed arrangements, ordering seeds, or even getting a head start on seed-starting, you may be looking at last year's seed packets and wondering if you can still use what's inside them.
In most cases, the answer is yes, but seed life varies depending on species. There's some disagreement among sources as to how long seed lasts, but here are a few resources you can refer to:
Iowa State University Extension
Virginia Cooperative Extension
Johnny's Selected Seeds
And a post from Margaret Roach's blog that draws together information from several sources in a chart and points out the disagreements.
However, it's pretty much agreed upon that onion, parsley, parsnip and salsify seeds only last a year, so go ahead and throw those packets away (unless you want to experiment). For the others, you may want to do a viability test, as described in several of the above links. Most instructions for this will tell you to try sprouting 20 seeds between moist paper towels inside a plastic bag, and then decide based on the percentage of successfully sprouted seeds how viable the remainder are. Since I often buy small packets to begin with, I often don't have 20 seeds left, or don't want to waste that many (often the viability test has to happen too early in the year for the resulting sprouts to be planted). In that case, I just use 10, or 5, or whatever number I can spare; the viability percentage may not be as accurate, but if they all sprout then you're good to go, if fewer than half sprout it's not worth it, and if it's something in between, it probably is, if you accept you'll get fewer plants than anticipated.
*Mention of specific products, brands, or companies is not intended as an endorsement by the University of Maryland.