If you have gardened for long, you have wanted to store seed for longer periods of time than what can normally be done by sticking the envelopes in a drawer. Perhaps you have purchased more seed than you need. Maybe you’re super frugal and just don’t want to waste any. Or, possibly, you possess a seed which is so hard to get that you might not be able again if your supply expires.
Let’s consider what factors after the shelf life of a given seed.
- The kind of seed makes a difference. Some seeds last longer than others. For instance, parsnip and onion seed expire very rapidly compared to squash or cucumber seed. Take a look at What Should I Do With Old Seed? and check out the link from Iowa State University. That’s a decent list of garden seed viability.
- Humidity affects the storage life of seed. High humidity shortens its life and low humidity (up to a point) lengthens it. We once spent some years in a cold rainforest environment. There, due to humidity issues, my seed often expired in less time than it took to go from harvest to planting time! TDS article on seed storage and humidity
- Temperature is a major factor affecting seed viability. Hot temperatures kill seed. Warm temperatures shorten seed life. Cooler temperatures extend seed viability. Provided that the seed is properly dried and sealed, seeds can be frozen for decades at a time with virtually no deterioration in viability.
- Light conditions affect seed viability. Darker is better.
So, lets talk about how to store seed for a long time.
- First, check how old the seed already is. Here’s another link with relative viability time for garden seeds. If it’s questionable whether it will grow, do a germination test.
- If the seed is still good, make sure that it is fully dry. One way to do this is to leave it spread on a tray, in a cool dry location. If already packaged, but possibly humid, try placing a couple silica packets in with them, in a sealed container, for a couple days.
- Seal the seed in something air tight. I prefer glass jars, but zip lock bags do work. Be sure to label the seed with variety, date and even when put in cold storage.
- Place the sealed container of seed in a cold environment, one which will remain consistently cold. A refrigerator helps greatly. Personally, I like to use a freezer. The best freezer is one which is dedicated to seeds, and not opened frequently.
That’s it. Many seeds, stored this way, will outlive the one who put them into cold storage.
Part of knowing how to store seed long term is knowing how to take it OUT of cold storage.
If seed is taken out of cold storage, it is important to warm it up properly, before opening the sealed container it is in. Take the seed, in its container, out of cold storage, and let it warm to room temperature BEFORE opening it. Some experts suggest that seed be left to warm for four hours before opening. To open the container before the seed has warmed will cause condensation on the seed, possibly ruining it. I once pulled a jar of beans from the freezer, and, in a hurry, I quickly opened it and poured out a little seed before closing it tightly and leaving it on the shelf, next to the freezer. I gave the seed I had taken to a friend, who planted it. It grew. But a month later, when I got some for myself, not a single seed germinated. In fact, they were all coated in a fine layer of mold.
When you carry the seed out to the garden, be careful not to leave it in the sun.
This is true for any seed, whether from cold storage or not. Seed sealed in glass or plastic will heat up very rapidly in the sun. It’s all too easy to kill it by over heating it. I have taken a jar of beans out to the garden to plant and been called away, leaving the seed, sealed an in the shade. But then, forgetting to get it immediately, I discover that the sun moved and the seed cooked. Be careful!
Barksdale Wax Pole Bean, our family heirloom surfaced in a frozen seed bank after more than 31 years. It was fun to grow the old seed alongside what we have been growing for decades.
Anecdote about long term seed storage:
Back in 1985, as a new seed saver, I corresponded with a friend in Oklahoma, exchanging seed. I sent him seed of a tomato and a squash which were special to me. In 1987 our family left for basically 14 years in Mexico. During that time I lost those two varieties. In 2002, I found an old letter from my friend and upon establishing contact, he sent me seed which he’d had frozen since 1986 (16 years). All my seed had expired. It wouldn’t grow, but his seed grew as if it were freshly produced. I recovered my varieties. This is the beauty of cold storage! Other friends have grown seed stored for 40 plus years.
If you love seeds, why not consider starting your own frozen storage unit?