Sarah Smith, NC State Extension Master Gardener^SM volunteer intern of Durham County

(Image credit: Allie Mullin)

This article was originally published in: The Gardeners Buzz: Newsletter for the Extension Master Gardeners Volunteers of Durham County^SM in April 2024.

I was recently asked this question from someone who saved his seed in the freezer for many years until he read an article stating that seeds should never be frozen, but stored in the refrigerator. I keep them in a box in my office. Which way is best?

The answer is all of the above. Each method has advantages and disadvantages. However, the goal of all three is to keep the seeds from starting the germination process because once it begins, the embryo will die if it doesn’t have what it requires to continue growing. What begins germination is warm temperature, moisture/humidity, and light, so seeds need to be stored in a cool, dry, dark place. The refrigerator, the freezer and my seed box in the office all provide darkness, so I won’t go into that aspect.

Moisture is the first element that begins germination, so no matter where you store your seeds, they should be kept dry. I keep desiccant packets in my seed box to wick away any excess moisture. Paper envelopes helps to keep them dry also. Whether you store them in the freezer or refrigerator, it is recommended that you place the paper envelopes and a desiccant in an airtight container. When taking them out, let the jar come to room temperature before you open it. Opening it beforehand may cause the packets to absorb moisture generated by the thawing process. Add warmth to moisture and you either have germination or mold, which is why it’s
recommended to keep them cool. The question is, “How cool?”

Some resources say that freezing will kill many seed varieties. Others say that freezing is a great way to store seeds. Both are correct, but under different circumstances. Temperatures between 35 to 40 degrees F, are optimal for most seeds, so storing them in the refrigerator will prolong their viability. If you’re going to be periodically taking them out and then returning them, then this is your best option. Thawing and refreezing seeds are stressful for them and may result in decay. Keep them dry with an airtight container and maybe desiccants. Craft supply stores sell silica gel in bulk in the dried flower section. You can also use powdered milk wrapped in cheesecloth. Replace it about every six months.

If you are storing seed for a long period (up to 10 years), then you can use the freezer with a caveat: it must be dried to 8% moisture content. Even a small amount of moisture may be enough to crystalize inside the seed coat and kill the embryo. This is what seed banks like Svalbard do. However, it may be difficult to accomplish and maintain in a home setting. Before freezing them, make sure they are thoroughly dried, then place them in a sealed container with a desiccant for three days. You can also dry the seed at 100 degrees F for six hours. Do not use the microwave. Because the seed must be dried before storing them, freezing is not an option for a small group of seeds that must maintain moisture to stay viable. Recalcitrant seeds cannot resist the effects of drying or temperatures less than 50 degrees F. Examples are pawpaw, avocado, mango, lychee, and cocoa.

What about the third option: leaving them unrefrigerated? The seed box in my office is a good option for me because it’s dry (in paper with desiccants), dark (in a box) and the temperature doesn’t fluctuate much. (If you can’t keep them cold, then keep the temperature consistent. Fluctuating temps can mimic the changing seasons.) Other suggested unrefrigerated places are kitchen cabinets, closets and basements. I also use my seeds up quickly, so long term storage is not a concern for most of them. I do use the refrigerator for some of my seed

The refrigerator satisfies all three criteria without the added precautions of freezing. They store longer than in room temperature and when properly contained, they stay dry. Refrigerated seeds can be taken out and returned without the hazard of freeze-thaw-freeze damage that taking them in and out of the freezer causes.

Freezing seed also satisfies all three criteria, but with extra precautions such as maintaining the moisture level at 8% and using airtight containers. Under those conditions, your seed can stay viable for up to 10 years. However, it is not recommended for most gardeners who tend to get into them on a regular basis which causes damage to the seed. Also, it takes lab equipment to determine that the seeds are dried to the right percentage of humidity before storing them.

In conclusion, stored seeds need to be dry, dark, and either in cool temperatures, or consistent temperatures. How you decide which is best for you is determined by your environmental factors. Do your research and then experiment.

References
University of Minnesota – saving vegetable seeds
Utah State University – collecting and storing seeds from your garden
Carolina Farm Stewardship – how to store vegetable seeds long term
Colorado State University – storing vegetable and flower seeds
USDA.gov – how long do seeds last.
West Coast Seeds – storing seeds

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