How long do heirloom seeds remain viable?
Written by
Benjamin Miller
Reviewed by
Prof. Martin Thorne, Ph.D.Knowledge of the viability of heirloom seeds can save you from the disappointment of seeds that do not germinate. The viability of heirloom seeds can greatly differ between species, and even depending on how they are stored. For example, my Cherokee Purple tomato seeds will remain viable and germinate for up to six years, provided the seeds have been stored properly. In contrast, onion seeds are usually only feasible for one season. Good methods and techniques can make the difference between success and failure each time you plant heirloom seeds.
Storage Fundamentals
- Temperature control: maintain 40°F (4°C) for longevity
- Humidity management: below 40% relative humidity prevents mold
- Absolute darkness: UV light degrades seed embryos rapidly
Species-Specific Longevity
- Tomato family: 4-7 years viability potential
- Alliums: 1-2 year maximum viability window
- Beans/peas: 3-5 years with silica gel protection
Viability Extension
- Silica gel packets absorb moisture effectively
- Vacuum sealing reduces oxygen exposure damage
- Freezer storage doubles longevity for most varieties
Reasons for inheritance are more important than seed age for longevity. Consistent temperatures of 40°F (4°C) or lower, along with humidity levels of 40% or lower, are the goal. I use mason jars with silica gel packets that I change every year. This has kept some seeds viable for over twenty years, such as the Moon and Stars watermelon seeds that I sowed a couple of years ago, which germinated successfully.
The characteristics of life forms create differences in viability in nature. For example, tomato seeds have a protective gel coating which helps them last longer. In contrast, fragile allium seeds, such as onions, decay much quicker. You can check the viability of older seeds on hand the classic way: the float test. Viable seeds sink; seeds that are no good float. This check is simple and may be valuable in avoiding time wasted planting.
The storage life of seeds can be extended significantly by storing them in the freezer. Dried seeds can be placed in vacuum-sealed bags with all the air removed. Then keep frozen at 0°F (-18°C), and biological activity is effectively suspended. I have frozen beans from my Cherokee Trail, and had an 80% germination rate, even after eight years. Always allow your seeds to thaw gradually before planting them.
Today is the day to start saving your seeds! Be sure to label each batch with the harvest dates, and use the oldest seeds first to rotate your stock. Take part in seed exchanges to periodically refresh select genetics. When you practice proper techniques, your heirloom seed collection will become a lasting legacy!
Read the full article: Heirloom Seeds Definition: Core Insights
