Conditions for proper seed storage are basically the opposite of what seeds need to germinate. To grow they need moisture, warmth and light; for storage they need cool temperatures, dry atmosphere and darkness. Most seeds will last for about three years if stored properly. Often they last much longer.
What should you do if you have some seeds that have been lying around for several years and you are not sure if they will germinate? There is a simple way to test a seed’s viability before you prep your seed trays and waste your seed sowing medium on something that has little life left in it.
Moisten a few paper towels with water. Place a dozen or so seeds spaced apart on the towel. Then either hold on to one of the edges of the paper towel and roll it up into a spiral or place a few damp paper towels on top to create what looks like a seed-germination sandwich. Either way the seeds need to be encased on both sides by damp paper towels.
Place the towels in a plastic bag or plastic container and don’t seal all the way (allow a small amount of air to get in). The idea is to create a moist chamber for germination while allowing for some air circulation.
Leave the container in a warm spot (such as, perhaps, the top of your refrigerator) and check it every few days. If the paper towels start to look dry, remoisten them with a sprayer.
The seeds should take one to two weeks to germinate. Once they have germinated count your success rate. If less than 50% of the seeds have germinated, then they are probably not worth sowing. If 50% to 80% of the seeds have germinated, they are viable but you’ll need to sow more thickly than you normally would. If the germination rate is higher than 85%, sow as you normally would.