1. To set up the test, layer several sheets of paper towel. With a waterproof pen, mark a grid of 100 squares (or 50 or some other easy fraction of 100, but not less than 20) on the top sheet. Wet the towels until damp but not soaked.
2. Place one seed in each square. For most seeds, cover the test grid with several more layers of damp paper towel. Some seeds need light to germinate; the packet will usually tell you. For these, skip the covering sheets. Carefully slide the test sheet into a clear plastic bag (a one-gallon Ziploc bag works well). Keep the rest of your seeds stored in a cool, dry spot.
3. Close the bag without completely sealing it. You'll want a little oxygen to get in.
4. Place the bag in indirect light at 75°F to 80°F. The top of a refrigerator or water heater often works.
5. Wait three to four days for quick germinating seeds such as squash or cabbage, and as long as two weeks for slower germinating seeds like parsley or carrots. When sufficient time has elapsed, check the percentage of seeds that have sprouted. If more than 50 percent sprout, the rest of your seed stash is worth planting. To get the number of plants you want in the garden, take into account the germination test rate (if you have a 50 percent germination rate and want 100 plants, plant 200 seeds). A germination rate below 50 percent is your call. If the seeds are a common variety, buy new ones. If you have a rare or special variety, at least you'll know what to expect come growing season.
Stella Otto is the nationally recognized author of The Backyard Orchardist and The Backyard Berry Book.