The Shelf Life of Herb Seeds

Seed Saving

• Generally, saving your own seed is the only way you can be certain how old the seed is to start with. Most seed packages say only what year the seed was packaged for, not what year it was harvested. When harvesting your own seed, remember to only harvest from healthy plants. Although a small amount of stress can increase seed set, it's not worth taking the chance that the seed will not be as viable by stressing your plants. Generally, unless you're trying to breed a new variety, hybrid seeds shouldn't be saved, as they will not breed true. When saving your own seed, ensure they have finished maturing before harvesting and dry the seed well to reduce the chances of mold or mildew.

General Herb Seed Information

• Herbs are generally woody perennials, herbaceous perennials or annuals. Woody perennial seeds, such as those from rosemary, sage, thyme or lavender, are generally viable for five to 20 years. Herbaceous perennial seeds, such as chives, ginger, lemon balm, or ginseng, have a much wider shelf-life range, from several years to several decades, with some woodland species remaining viable after decades in the soil. Annual herb seed, such as seeds from basil, borage, mustard and dill, stays viable for one to two years.

Refrigeration

• To increase the shelf life of your herb seeds, seal them in an airtight container, such as inside a plastic bag stored in a mason jar, and keep the seed refrigerated, but not frozen. It's important to keep the seed as dry as possible, so add a silica packet to the jar if the air was humid when you stored the seed. While you can't freeze the seed in a normal freezer, it is possible to cryogenically freeze the seed if you have access to the right equipment. Some seeds need to experience a cold period, or stratification, before they will germinate.

Testing Viability

• The seeds in a package usually don't stop being viable all at once. The best thing to do, if you're unsure if you have enough seed, or you want to know how many seeds to plant to get a certain number of plants, is to test the herb seeds' viability early enough to be able to order more if needed. Normally, you would test seed viability based on 100 seeds; however, if you are working with a smaller amount of total seed, test 1/10 of your seed. To tests for viability, soak your seed in water for four hours -- overnight for some large, heavy-coated seeds -- wrap them in damp paper towels and seal in a plastic bag. Put the seeds in a warm location, like the top of a refrigerator, and check your seeds every other day. At the end of the predicted germination time on the seed packet, calculate what percent of your seed has germinated.