Stamina for Shelf Life Varies by Seed Variety

It is wasted effort to sprinkle dead seeds into furrows in the garden or in flats. Good seeds are alive, but they don’t live forever.

When you buy a packet of seeds, be sure of their freshness. There are government standards for the minimum percentage of seeds that must germinate for each type of seed.

The packing date and the germination percentage often are stamped on the packets. (Germination percentage must be indicated only if it is below standard.) If the packet isn’t date-stamped, write the purchase year on it.

Depending on where you kept them, your old dogeared seed packets may be worth using this season.

Low temperature and low humidity slow seed aging, making it a good idea to store seeds in sealed containers in your freezer or refrigerator. Canning jars or plastic freezer containers work well. An easy way to keep the humidity low is to sprinkle powdered milk, from a freshly opened box, onto the bottom of the containers. Renew the powdered milk each year.

Seeds differ in how long they remain fresh. Even with the best storage conditions, it is not worth the risk to sow parsnip or salsify seeds after they are more than 1 year old. Two years of sowings can be expected from packets of carrot, onion and sweet corn seed; three years from peas and beans, peppers, radish and beet; and four or five years from cabbage, broccoli, Brussels sprouts, cucumber, melons and lettuce.

Among flower seeds, the shortest-lived are delphinium, aster, candytuft and phlox. Packets of alyssum, Shasta daisy, calendula, sweet pea, poppy and marigold can be stored five to 10 years before the seeds get too old.

A yearly germination test each spring can tell you if an old seed packet is worth saving. Count out at least 20 seeds from each packet to be tested, and spread the seeds between two moist paper towels on a plate. Invert another plate over the first to seal in moisture. After a week or two at 70 to 75 degrees, peel apart the paper towels and count the number of seeds with little white root “tails.” Figure the percentage, and either throw out the seeds or adjust your sowing rate.

The record life-span for seed longevity is held by a species of lupine whose seeds germinated after 10,000 years. Such lengthy seed survival is rare. In this case, the lupine seeds were unearthed from animal burrows in the Arctic permafrost.

Stories of plants growing from hundreds- or thousand-year-old seeds found buried in ancient Egyptian tombs or ancient pueblos of the Southwest are fiction.

Fifty years ago, French scientist T. Becquerel studied the viability of seeds that had been held in storage with the National Museum of Paris. The oldest to germinate were 221-year-old mimosa seeds.

At the other extreme in longevity are seeds such as those of swamp maple, which retain their capacity to grow for only about a week.