Long-term storage

General Discussions
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Hi !

I am starting to accumulate a small stock of seeds and wonder about their long-term conservation.

Indeed, despite my context as a market gardener I do not have the possibility of renewing these seeds sufficiently to my liking. Knowing that these seeds are intended for my future seed production project.

My colleagues have been freezing our bean and salad seeds for several years. The germination rate does not seem to be changing but I still wonder about the limits of the technique. I know that it is used by some conservatories so I suppose it is just apprehension, but have you already tried this method and if so what is your feedback?

Are you aware of any impacts on the quality of seeds or plants and what about the storage capacity after defrosting? What are the points to watch out for?

Thank you and wish you a nice day!

EDIT : At the moment some information is quite contradictory. On the one hand I find that this can kill our seeds (because these preservations are generally carried out in laboratory conditions), on the other I read articles which emphasize the beneficial side and they even give procedures. For example this one used by the Jardin Conservatoire du Revermont in Ain (France).

  • Dry the seeds well. Very important!
  • Then bag them in paper.
  • Put everything in a perfectly airtight plastic box (like Tupperware)
  • Store in the freezer at –25°.
  • So the seeds will keep for more than 30 years.

What do you think ?

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I would like to learn more about this myself!

I have always heard that seeds can stay viable for a long time when stored properly in the freezer. It’s never been elaborated on.

I never wanted to risk it, so I have never done so. I am terrified that if I put my collection inside the freezer, I would do so improperly and there goes my collection.

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We store only some bulk seeds in the freezer. We divide them up so we only need to defrost a small amount at a time. We haven’t been doing it for very long so I don’t know the long term effects.
Most of our seeds are stored in a very well insulated room which doesn’t have big temperature swings. I think the humidity is also fairly stable but we don’t measure either.
We try to use the seed as soon as possible and once they go past their sow by date we either feed them to the chickens or sow them as part of a green manure.

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Carol Deppe’s book “The Resilient Gardener” goes into instructions for storing seeds longer-term; I don’t have it to hand at the moment but it might be worth a look.

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Just one thing I retained from a seedman is that freezing seeds must be under 8% humidity content. Which is to me - as I don’t have something to measure - very dry. Otherwise some seeds may break when freezing them, as the seeds expands proportionnally to the water content. Then it is better to store them in plastic otherwise when defrosting seeds humidity in the air will condensate on them.

Last thing I retained from various persons, is that you can freeze seeds temporarily to make sure you kill all insects - for example weevil - which I did one month ago when I saw part of my seeds attacked… So I took all my legume seeds and zipped them altogether in different big zip bags, and froze them. Then I defrosted then one week ago, still in the zip bag. It went fine.

Also I was wondering if a machine for vaccuum packing, or mylar bags + silica gel would not be another way of doing long term storage, without a need for a freezer, which can break down, or the electricity can go down.

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To me , this is the best resource ever on seeds, translated in about 10 languages: Films | Diyseeds (but: they teach how to keep pure lines, not how to landrace species…). Made by an NGO like Gts, and also accesible for free.
Still, they didn’t make a video about the storing stage in their “ABC of seed production”. But, there is always advises at the end of videos, of which some about storing. In these, they always suggest to “put the seeds in the freezer for a few days to kill parasites”. Prior to that, thay expressly explain how to do a “good” drying.
The point is that, with this video, they make all things simple. Which is great!

So my hypothesis is that the contradiction may be due to drying problems (and maybe containers also, for the defreezing stage, as written above): if not done properly, you may end up harming your seeds.

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It does, and I decided to take to heart her advice to make an archive of my best seeds from my garden every year, so I can always go back to an old population if I need to. Ever since I lost a computer when I was a teenager, I have strongly believed in the value of backups! :wink:

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we are helped in our association on the seed bank part with a professional seed company for 40 years for Kokopelli. She advises us to spend sensitive fleshy seeds like beans, corn… at least 15 days in the freezer to kill any predator.
We store our vegetable seeds in an old industrial drawer cabinet all year round at 12°C (53°F), in a cold room that we built ourselves with a lot of reclaimed insulation.
In July, just after the annual wheat harvest, we also lower our storage cold room to 5°C (41°F) for 1 month to avoid heating the grains stored in bags. This period combines the heat of the summer that provides energy to the solar and geothermal panels that makes the installation 100% energy self-sufficiency year-round. Another advantage of the cold room with its airtight metal partitions, we no longer have any insects or mice entry and this is really important when you start storing large quantities of seeds

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Thanks Stephane! That sounds great. Could you give us a photo or 2 one day? I would love building such a self-sufficient installation! And I wonder how big it is.

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It’s not very aesthetic it looks like a room made of partitions seen from the outside, with about 10m2 to store the seeds of cereals and vegetables, our wheat crops, our production of apple juice and some drinks for the animations we realize.
I have to point out that the company that comes to us is a renewable energy installation company. We therefore take advantage of the know-how of a member, the used equipment that he recovers and recycles and especially the existing installation to make the local autonomous. It would not make sense to make a cold room autonomous by creating a geothermal and photovoltaic field. On the other hand with 20cm of insulation all around the cold group does not trigger often, it is really the key to the sobriety and stability of the internal temperature !

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Yes, that’s what we do for our beans in particular!

It crossed my mind too. If I can get my hands on a device I will probably give it a try. I will put seeds that degrade relatively quickly in a vacuum, and do a germination comparison with a package stored in a more traditional way after one or two years!

Yes it is very likely. I seem to have seen this “contradictory opinion” on the site of a seed company, which gave some conservation advice and was quite categorical on the impact of freezing. But maybe they didn’t even try!

I have just received his book in PDF format, given that the format is not the most practical to “browse through”. Could you point me to the passage dealing with storage in the freezer? I’ll capture it on my next post!

Yes, I am convinced by the value of a self-built conservation chamber. We already have one for vegetables and are quite happy with it. I haven’t yet looked into what form it will take for my seed production project, but it’s sure to be very interesting research! In any case, I am also interested in photos if you have any, even if it is not very aesthetic.

Thank you for these responses !

I would add that I did some research, and found this document:
FreezingSeedsData.pdf (151,6 Ko)

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blue: 8 days frozen Green: 0 days frozen
red: 5 days frozen Orange: 1 days frozen

I always assume that the results of a test can always be linked to several factors. We work with living things and that necessarily involves a complexity that we don’t have in a controlled environment. From the seed to an environment in full interaction. So, I put big quotation marks on this document. Despite this, we could confirm certain observations. We see in this graph in particular that the radishes did not withstand freezing, losing 30% germination rate in 8 days. Is it a constant dynamic with this type of seed, is the loss progressive or stabilizing, is it due to the protocol or to these very specific seeds (these “individuals”)? I don’t know, but if it’s a reality it’s probably worth looking into!

For those who freeze, have you had any problems with germination rates with certain seeds?

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I apologize; I have no idea! I have all her books in paperback, so I can’t digitally search them.

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It’s okay, I found the passage that interested us!

So, in the book “The Resilient Gardener” by Carol Deppe, from page 89 to 90:

In my freezer are gallons of seeds, specially dried and sealed in glass jars. Most of it is seed I have grown. Some is seed i have bought. I can expect that seed to last as long as the freezer and the electricity last plus (for the corn, for example) at least another ten years. I think it is a good idea to have such a backup supply of seed for all varieties that really matter to me, Whenever I come to appreciate some new variety, my first step isn’t saving the seed. My first step is simply buying extra, drying it properly, and freezing it. I don’t save seed of every variety I use. But i have learned how. And I do try to have a stash of every variety i use. Should it become impossible to buy the seed, I would have enough hoarded seed to grow a crop and to start saving the seed myself from that point on.
To freeze seed you need to be able to seal it in jars or other airtight containers. Much commercial seed is not dry enough for that. The seed continues respiring slowly, and needs oxygen.The seed needs to be dried more thoroughly, which puts it into a deeper state of dormancy. After the more thorough drying, the seed can be sealed in airtight containers and frozen. To get the seed dry enough to seal in glass jars or freeze requires a lower humidity than is found naturally in most places. So I dry our seed in a dehydrator at 95°F for the right amount of time, until the indicating criteria say that it is dry enough. The biggest indicator for corn and beans and other legume seeds is the “hammer test.” That is, take some seeds out to the sidewalk or driveway and hit a few of them with a hammer. If they shatter, they are dry enough to seal in airtight containers and to freeze. If the seeds smash instead of shattering, they are still too wet. The indicating criteria for dry-enough squash seed are a little more complex; I discuss them in the squash chapter. After you remove a jar of seed from the freezer, always give it a day to warm up naturally before you open it, Otherwise, moisture condenses on the seed, and it is too much of a shock. An added benefit of freezing seeds is that it kills insects and insect eggs. So freezing the seed for a few weeks is useful even if you don’t store any that way permanently. (A shorter freeze may or may not be sufficient.)
If you don’t have a freezer you can still hoard seeds. Dry them as described and seal them in airtight containers. Then replace each lot of seed with fresh seed occasionally. (For most seed, once every five years will do.) Store the containers of seed in as cool a place as you have. Hidatsa Indians hid caches of seed in the ground as they left summer villages for winter villages. I haven’t quite figured out how to store containers of seeds in the ground for more than a few years. (The metal lids would rust, Most plastic disintegrates.) But even a few years might be useful. I prefer to hoard seed I have saved myself. It is possible to produce hand-saved seed that is prime beyond anything possible on a commercial scale. Such seed has astonishing longevity and vigor. For example, six-year-old corn seed of mine that has been fully dried and stored in a glass jar at room temperature germinates faster and more vigorously than most freshly bought commercial seed. Last spring Nate and I planted six-year-old flour corn seed, most of which had been stored at room temperature. It was a breeding project, and we wanted every seed to count. So we spaced it carefully. Nearly every seed came up. I doubt if we were “missing” more than a dozen seeds in the entire field of a few thousand.

This confirms the importance of very dry seeds, an airtight container and keeping the container closed before complete defrosting! And I imagine she has enough feedback not to be worried about the outcome.

For the French who go through this, I have difficulty understanding the nuance between “smash” and “shatter” for the hammer test. Feel free to send me a little private message if you can enlighten me!

EDIT : And in the chapter on squash:

In chapter 4 i introduced the idea of hoarding seeds, that is, putting away a long-term, ideallyfrozen stash of seed of every variety you care about, whether you save seed of the variety or not. I didn’t start out with that policy. I started out, as most seed savers do, simply saving seeds of certain varieties and not others. Since I was actively breeding both pepos and maxes, I had to do lots of seed saving for my breeding projects. I figured I didn’t have to also save seed of the squash varieties that are widely available commercially. As should be graphically apparent from the rest of this chapter, that turned out to be a big mistake. No matter how widely used and available a variety is, we really cannot count upon the commercial supply. I did not actually need to save seed of every variety initially, however. It would have been sufficient if i had simply hoarded some of the good “storebought” seed of each variety I cared about. Then I could have used the hoard to start saving my own seed of a variety when something went wrong with the commercial lines. To hoard squash seed we have bought, we often need to dry it additionally. Refer to the section in chapter 4 for the basics of drying bought seed for freezing or storage in airtight containers. Omitted from that account was how to evaluate squash seed to see whether and when it is dry enough. The way to do this is to shell out some seeds and examine the seed shells and the meats separately. When the seed is dry enough, the shell is brittle, and the meat is also. The meat snaps clean when you bend it instead of bending. Very often, small seed such as is typical of pepos is easy to dry, but people often don’t dry the big seeds from the larger-seeded max varieties well enough. What happens with the latter is that it is easy to dry them to where the shell or whole seed is dry enough to snap, but the meat isn’t. The moisture content is too high. In addition, the moisture from the meat re-hydrates the shell in storage, often enough so that the seed molds if stored at room temperature. So to evaluate the dryness of squash seed, always shell some and test the meats.

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In case this helps:

Smash = The seed squishes when you hit it.
Shatter = The seed breaks into little pieces when you hit it.

If it’s moist, it’ll stay in one piece and flatten. If it’s dry, it’ll break into lots of little bits.

I hope that helps!

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here are some pictures of our cold room built in low tech mode and recovery.
the walls are made of compact insulation boards because they remained panels of the old company that sold cold solutions for manufacturers, the door is a real cold room also recycling the old stock, and as it was put under roof my colleague artisan renewable energies who hosts our association with 1 m of insulation on top.
Only the refrigeration unit is purchased. The electricity is 100% renewable produced by solar panels and geothermal energy.
We see our industrial furniture where we store our seeds, and above the small plastic lockers that are our mobile seed bank when moving on an event.
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@DebbieA shared a resource related to vacuum sealing seeds recently, for the purpose of long term storage. Particularly in humid environments. The article goes on to describe how to fabricate a vacuum sealer from a bicycle pump if needed. Vacuum-Sealing Options for Storing Seeds | ECHOcommunity.org

I remembered this thread so I thought I would ask. Has anyone here used a vacuum sealer for seed storage? It came up previously in the discussion but it seems like none of us has used this approach yet ourselves.

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I just came across this article and it reminded me of the conversation here. Very interesting:

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Apologies if it has been mentioned already, but a fundamental part is to the success of storing this way is to let the container return to room temperature before you take off the lid. This way the seeds and the inside of container don’t attract moisture and can be refrozen again if needed. I tend to not use dehydrator and haven’t noticed viability problems with homegrown or commercial seeds (though summers in my location tend to be low humidity). I store all seeds in the freezer.

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