Do Seeds Expire?

Gardening enthusiasts and professionals alike often find themselves with leftover seeds from previous planting seasons. The question that frequently arises is, “Do seeds expire?” While seeds don’t have a strict expiration date like perishable foods, they do have a viability that can decrease over time.

Understanding Seed Viability

Seed viability refers to a seed’s ability to germinate and grow into a healthy plant. As time goes by, the germination rate of seeds (i.e., the percentage of seeds that successfully sprout) generally decreases. This means that while older seeds might still germinate, fewer of them will do so compared to when they were fresh.

Factors Affecting Seed Viability

1. Seed Species: Different species of seeds have different lifespans. While parsley seeds might retain good viability for only one to two years, certain tomato seeds can remain viable for over a decade if stored properly.
2. Storage Conditions: Seeds stored in cool, dry places will generally last longer. High humidity and temperature can adversely affect seed viability. Prolonged exposure to these conditions can accelerate seed degradation.
3. Seed Maturity: Fully mature seeds harvested at the right time have a better chance of remaining viable for longer. Immature seeds often have reduced viability.
4. Disease and Pest Damage: Seeds that are damaged or infected by pests or diseases may have a reduced shelf life or might not be viable at all.

How to Test Seed Viability

If you’re uncertain about the viability of old seeds, you can perform a simple germination test:

1. Place about 10 seeds on a damp paper towel.
2. Fold the paper towel and place it in a plastic bag, ensuring it remains moist but not waterlogged.
3. Keep the bag in a warm spot.
4. Check the seeds after a few days to see if any have sprouted. The number that germinates gives you an approximate germination rate. For instance, if 7 out of 10 seeds sprout, you have a 70% germination rate.

Tips for Storing Seeds

1. Refer to the Seed Packet: Always check the seed packet for any “packed for” or “sell by” dates. While this doesn’t strictly indicate an expiration, it can give you an idea of the seed’s age. Additionally, the packet often provides specific storage advice for that seed variety.
2. Cool and Dry: Store seeds in a cool, dry place. A popular method is placing seeds in airtight containers or sealed plastic bags and keeping them in the refrigerator.
3. Avoid Direct Sunlight: Exposing seeds to direct sunlight can reduce their viability. Always store them in a dark place.
4. Labeling: Always label your seeds with the name of the plant and the date of collection. This will help you keep track of their age and potential viability.
5. Oxygen Absorbers: Consider using oxygen absorbers in seed containers. These can help prolong the shelf life of seeds by reducing oxidative damage.
6. Regular Check: Inspect stored seeds periodically for signs of mold, pests, or any other issues.

The Beal Seed Experiment at MSU

Michigan State University’s (MSU) Beal Seed Experiment, started in 1879 by Professor William James Beal, offers unique insights into seed longevity. Beal buried 20 bottles filled with seeds and sand on MSU’s campus, intending to unearth one every five years to test germination. While many seeds lost viability over time, astonishingly, some, like the moth mullein (Verbascum blattaria), germinated after over a century. This experiment highlights the remarkable resilience of certain seeds.

Conclusion: Do Seeds Expire?

So, do seeds expire? The answer is nuanced. While seeds don’t “expire” in the conventional sense, their viability does decrease over time. Gardeners can take proactive steps to extend the shelf life of their seeds by following proper storage protocols. Moreover, it’s always a good idea to periodically test the germination rate of older seeds before planting them extensively in the garden. By understanding seed viability and how to maintain it, gardeners can make the most of their seed collections year after year.