By E. Vinje, our esteemed guest blogger from Planet Natural in Bozeman, Montana
How long seeds last depends on the type of seed and the conditions in which they’re stored.
Your thrifty Planet Natural blogger has had good luck storing leftover seed (PDF) he’s purchased from year to year … except when he didn’t. Not too many years ago, we stocked up on spinach seed for all the repeated planting we’d planned. There was plenty left over — that summer was cool and damp, so our first crop took longer than we expected and our second crop barely leafed out before the first frost arrived. We stored our leftover seed as we usually do: inside its packet in a tightly sealed glass jar down in our cool basement.
When spring came around, we planted the seed we bought the year before, just as we’ve often done with the previous season’s extras. And even under near ideal growing conditions — we know because we kept track in our journal — we were rewarded with poor germination. The seed that did germinate didn’t do well, its leaves small and stunted. We wondered if we had too much nitrogen in the soil. Too much nitrogen often inhibits early germination of greens. But the lettuce we planted nearby, some of it from saved seed, did just fine. Could it be that spinach seed doesn’t keep as long as lettuce?
Well it could, maybe. Or maybe not. It depends on who you ask. This great chart assembled by Margaret Roach for her blog How To Garden.com shows just how little agreement there is about how long seeds will last? One year, according to Johnny’s Seeds. If you ask the Iowa State University extension office? Five years.
So who’s right? I’d had grown spinach previously with year-old seed. And I’ve grown tomatoes from seed that was at least four years old. Often the storage conditions dictate how long seed lasts. Seeds stored in damp packets or conditions will deteriorate, and maybe even grow mold. Making sure seed is dry before you store in a Ziploc bag, a plastic sandwich container, or jar, any of which will seal in moisture if the seed is damp. And frequent temperature swings will strain seeds. That’s why the basement is perfect. I don’t keep them in the refrigerator as do some of my friends. Nor do I freeze the seed for a few days after bagging, as some recommend to kill pests. I’m afraid that freezing might cause damage to seeds not perfectly dry.
Gardening guides will tell you to do a germination test to make sure your seed is viable. You know the drill: place seed between a folded paper towel and keep the towel moist. A saucer with a little water, or sealing it inside a baggie, makes it easy. If the seed sprouts within its usual germination period, it’s okay.
Note: All heirloom seed varieties offered by Planet Natural are non-treated and non-GMO. Planting instructions are included with each packet. Shipping is FREE!
But germination is only part of the problem. Seeds lose strength as they age (sound familiar?) and even if they germinate they may not have the vigor to produce the kind of harvests they did when they were new. Remember my stunted spinach? These weaker plants are also easy targets for pests and disease. Organic gardeners want their plants to be as strong as possible.
So may we make a suggestion that goes against our otherwise frugal principles? Play it safe. If a seed’s viability is generally agreed upon to be a couple three years, like celery, peas, and corn, don’t take a chance. Buy new. Even if your seed does germinate in the ground, it might be slow to grow and produce inferior harvests. But if the seed is the type that’s good for three years and more, like beets, broccoli, cucumbers, and tomatoes (which can last longer than five years) then why not? Most of these plants are started indoors anyway, and you’ll know right away if something is amiss.
All bets are off when saving seed from your own garden, as many of us are starting to do (and many have done since their grandparents taught them how). As long as the plant isn’t a hybrid that won’t replicate in true fashion, we’re fine. And our home-raised heirloom seed? Priceless. We’re going to keep those tomato seeds that gave us those juicy, flavor-packed fruits for as many years as it takes to replace them. And that might only be one. But saving seed from the garden is a whole other topic. Let’s talk later.