The question many new gardeners probably are asking about now is “Can I sow the leftover seeds I purchased last year, or do I need to buy entirely new ones?” Their viability (ability to sprout—or not!) will depend on which you saved.
Vegetable Seed Viability
Among vegetables, the seeds of leek, lentil, onion, parsnip, rhubarb, and salsify generally don’t keep well—nor do dandelions. (Yes, some people actually plant dandelions!) So you should purchase new ones of those. If you harvested your own seeds from open-pollinated cultivars in 2020, they would be equivalent to “new” seeds (those packed for 2021).
Old sweet corn seeds also can be a bit if-fey, so it’s a good idea to buy a fresh supply of those. You’ll need them to come up heavily to make up for all the kernels the birds steal! After two years, you may want to think of investing in new bean, beet, chard, okra, pea, and pepper seeds too.
Many other vegetables fall into the 3 to 5 year category, so you could get good results with them using old seeds, as long as they aren’t verging on ancient! Those which may still sprout in their 6th year include vine crops such as cucumber, melon, pumpkin, and squash, while some tomato seeds can hang in there even longer.
Herb Seed Viability
As for herb seeds, the short-lived angelica, caraway, chives, fennel, and parsley ones should be sown in the year for which they were packed. Herbs whose seed could remain viable right up to years 3 or 4 include basil, catnip, chamomile, lavender, lemon grass, and oregano. Most others fall somewhere in between, meaning that they may or may not sprout after their first year.
Flower Seed Viability
Flowers for which you should purchase fresh seeds include annual geranium, aster, black-eyed Susan, columbine, delphinium, impatiens, larkspur, pansy, phlox, salvia, strawflower, and verbena. I’d also add sunflower to that list, because the only old Helianthus seeds which sprout well for me are those stored in foil packets.
Flower seeds which can germinate when as old as 4 or 5 years include: amaranth, bee balm, calendula, eucalyptus, euphorbia, morning glory, and stock. As with vegetables, many of the others fall into the 3 to 5 year category. Keep in mind that pelleted seeds should be used in the year for which they are packed, if possible—though I have had some sprout pretty well for me in their second year too.
To maintain seeds in their freshest condition, many sources recommend that you store the packets inside a glass jar, capped with a tight-fitting lid, in your refrigerator. For the best results, include a layer of a desiccant such as uncooked rice or powdered milk at the bottom of the jar. If you intend to try this, I would recommend a large, wide-mouthed jar, or you'll have to bend the packets quite a bit to jam them in.
I must admit that I don’t refrigerate my seeds, mainly because there’s too much stuff in our refrigerator already, including seeds being stratified in damp paper towels! Fortunately, dry seeds still will store pretty well if you keep the packets in a dark, moisture-free, and relatively cool place—preferably at temperatures not higher than 70 or so. Mine generally reside inside an accordion file in an old trunk.
Storing Seeds Damp
If you are collecting your own seeds, keep in mind that some species don’t endure dry storage well. This especially seems to apply to wildflowers including bloodroot, celandine, spring beauty, trillium, and twinleaf. A solution to that problem would be to sow the seeds immediately after harvesting them or to store them in damp vermiculite instead.
Variability of Viability
Of course, they are often as unpredictable as people. I just was reading an article in Guideposts magazine about a man from New York state who found 80-year old hibiscus seeds, which had belonged to a previous owner of his house, and managed to germinate one of them. (They had been stored inside an old tin with a tight-fitting lid on a shelf in a detached garage.)
My sister currently is experimenting with reviving old tomato seeds by a method she found online, which advises that the seeds be soaked overnight first in water to which a few drops of liquid plant food—either chemical or organic—has been added. The nitrogen involved supposedly helps stimulate germination. So far it hasn't worked on her extremely elderly seeds, but you might want to try it on some which are just middle-aged instead!
Just for fun I decided to try soaking several varieties of "packed for 2020" impatiens seeds in both gibberellic acid and a vitamin-based plant stimulant this year to see if any of them would germinate. Two were types I received in trade and the others some I harvested myself in 2019. The only ones to sprout thus far are my own. Three of the acid-treated seeds came up and one of the stimulant-treated. (The acid is a little more risky, though, as it can cause some seedlings to become elongated.)
Still, if you are hanging onto aged seeds which have sentimental value to you, I would try planting a few of them. You never know what might pop up!
Photos: The photos included in this article are my own.