ITG seed viability

To sprout into vigorous seedlings like these, seeds kept in storage must maintain viability, which is dependent on a variety of factors.

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Anyone who has gardened long enough likely has a pile of seed packets squirreled away with intentions of using those seeds someday. Many times I keep seed packets in my collection because I just can’t stand to throw things away, especially seeds that may have a viable, living plant embryo inside.

However, it can be tricky to figure out exactly how viable my old seeds remain in storage. With all the time that carefully goes into preparing a garden bed, I rarely have the guts to sow many of the seeds from years’ past for fear that my efforts will go to waste. So many times, I wind up buying new seed while the old packets remain in my collection, creating a conundrum of sorts.

Most of us think of seeds as dormant, inactive structures with potential to grow but not much going on in the meantime. However, a seed’s viability is tied to its ability to respire slowly, using stored sugars to sustain this process until the time is right to initiate growth.

Remember, respiration in plants is kind of like the opposite of photosynthesis. During respiration, plants use the sugars generated during photosynthesis, combined with oxygen, to produce the energy (plus carbon dioxide and water) that fuels all plant processes.

A seed must use energy to remain viable, but they lack the leaves needed to conduct photosynthesis and produce additional sugars, or energy. So seed viability is related to the ability to sustain respiration using stored sugars from past photosynthesis the parent plant performed. While this occurs very slowly, there is limited amount of time it can continue, as there is finite amount of stored sugar in each seed.

As with so many things in nature, there are plenty of other variables beyond the amount of stored sugars that affect seed viability. Environmental factors, such as humidity and temperature, play a major role as well. Past research has identified the optimal storage conditions for seeds, which requires low temperature and low humidity to slow metabolic activity and keep seeds viable.

The Global Seed Vault, located halfway between Norway and the North Pole on a remote island in the Svalbard archipelago, represents one of the largest seed collections in the world. With seeds from more than 1 million species from nearly every country in the world, it is vital that this vast collection of plant genetics maximizes the life of its seeds.

The location of the vault was a strategic choice, since permafrost helps the underground facility maintain a steady temperature near 0 degrees. The cold temperature also helps keep humidity low, which creates the ideal seed-storage environment.

I often get questions from folks wondering if they should plant old seeds or not. Many assume there is a shelf life for each species and it’s as simple as looking back to when the seed was bought to determine viability. However, storage conditions have a major effect on viability, so the answer is not so simple — it all depends.

Since none of us have a true seed vault designed to maintain optimal conditions, storage in a refrigerator or freezer is probably the most practical. It pays to keep seeds in a tightly sealed container, such as a zip-close bag or jar with a screw-tight lid, to limit fluctuations in humidity.

Without the benefits of permafrost, it’s safe to assume that many garden seeds will last for one year in storage. By the second year, there is most likely a loss in viability, but to some degree, it is predictable. By Year 3 in storage, all bets are off.

Under average storage conditions, simply a cool, dry place, you can assume the storage life of many common vegetable seeds as follows:

  • Viable for one year: beans, broccoli, carrots, corn, most herbs, leeks, lettuce, okra, peas, peppers, spinach
  • Viable for two years: beets, cabbage, cauliflower, cucumbers, eggplant, kale, melons, pumpkins, radishes, squash, swiss chard, tomatoes, turnips.

Ryan Pankau is a horticulture educator with UI Extension, serving Champaign, Ford, Iroquois and Vermilion counties. This column also appears on his ‘Garden Scoop’ blog at go.illinois.edu/GardenScoopBlog.

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