A Guide to Long Term Seed Preservation
Small Scale Seed Drying Methods
Seeds Eye View Cleaning and Storage
In my research I referenced the two above links for information of which I will paraphrase, customize and summarize for preppers in this article.
As preppers we store things for future use right? We preserve food and we can keep seeds for longer term use. You can buy seed banks in buckets. But what does it really take to store seeds for the long term and how long can they be stored for? We already know some of this from prepping. But we might want to take a look at what seed banks do. They use the following techniques.
- Hygroscopic desiccants
- Freeze drying
- O2 absorbers
- Full or partial vacuum
- Freezing -20c, 0f
- Cryogenic Freezing -200c, -330f
- Refrigerating 33f to 45f
- Anti-fungal treatments
First there are two types of seeds and then some that are in between. They call the type that tolerates ultra drying Orthodox seeds. Seeds that can’t take drying are called Recalcitrant and require moisture between 15 and 20%. Some seeds can take some drying or slow drying. Ultra drying is getting moisture content down to 1% to 2% or so. The seeds you may dry more tend to be all the smaller seeds. Pumpkin seed size and up tend to be ones that need more moisture. Plants that grow in rainforests and on riverbanks usually have seeds that need more moisture. That makes sense because their environment is very moist.
For the ones we may ultra dry, silica gel may be used. A chemical is added to the gel that can indicate moisture content by color change. To dry, it’s a matter of replacing the gel over and over until there is no more color change. This, of course, needs to be in a sealed container that won’t breath. Glass with a rubber sealed glass lid seems to be a container of choice. I don’t see why metal lids wouldn’t work; however, the lid needs a coating inside to separate the metal from the air. This coating might be rubber or plastic or some paint maybe. Plastic alone will breath. I was thinking pill bottles might be good for seed storage but probably only for the short term. They are made for 30 to 90 day use, not 40 to 100 years. Also, by using glass, you may inspect the seeds and color of the gel to ensure that moisture has not broken through the seal.
Freezing can help and won’t hurt except with the seeds that require moisture. Temps of 0F or -20c are best. Even when freezing, seeds should be protected from oxygen and ethylene gas which they produce as they age. Use O2 absorbers. They should still be protected from moisture even when frozen. Use silica gel. However freezing can be overkill and may not be necessary at all. They have tried freeze drying and it works, but is far more costly than simply using desiccants. But I’d say at least keep the jars from light in ground temperature storage. Use a root cellar for example. Remember the reason to use any cool, cold, or freezing temperature is to slow down fungal attack or rot and decay.
For the seeds that need higher moisture content cryo-preservation freezing at(-328f) -200c may be the only practical yet ***not*** cheap method for long term. Recalcitrant seeds, if not frozen, they can be kept in cool refrigerated temps up to near freezing which help, but they must also be protected from fungal growth and such.
It would be nice if we could put seeds in a jar, screw on a lid and then use those seeds with 100% germination rate any time for the rest of our lives. Sadly seeds simply don’t last. However seeds have been found in the great pyramids and germinated after 2,000 years in storage! The seed bank methods can keep seeds for 40 to 100 years or more. And most of the general info I have read about keeping garden seeds show 1 to 5 years unless you use seed bank extremes.
To recap a bit, the factors that affect seed longevity seem to be presence of oxygen and gasses produced from aging, as well as moisture. Temperature seems to be more of a problem with the seeds requiring more moisture. Fungal attack is yet another factor for the seeds that have to be stored higher in moisture content.
Pre-drying in the sun or using warm dry air is one method. I’m not sure that a home dehydrator would work as the temps may be too high and kill the seeds. Also it seems we should use cloth or paper bags to contain the seeds when drying to have better air flow around the seeds. These bags should be on a rack or screen which would also allow better air flow.
Desiccants are little packs we throw in buckets of food to keep them dry. Gel packs, iron based desiccants, O2 absorbers, rice, chalk, powdered milk, rock salt, and charcoal are things that come to mind. I really like the idea of using charcoal because I can make that at home. Many desiccants can be reused by heating them in an oven to drive off the moisture. As I said before, there are silica gel desiccants that are treated so that they change color when moisture is above 2% or so. Small packs of these added with other desiccants can be used as indicators as to when to change out the desiccants and to when we reach ultra dry state.
We can use an attachment for canning jars for a vacuum packer machine such as the ones we can get from Cabella’s or WalMart. We can store the seeds under a vacuum. However, silica gel or other desiccants still need to be used in the jar. Canning jars can indicate a lost vacuum by popping upwards on top. Silica gel can indicate moisture that is too high. Replacing oxygen with CO2 or nitrogen is not practical in most of our homesteading situation, I’d say. At any rate, looking at how seed banks store in tubes, I’d say we need to do the same in jars. Layer seeds on bottom, then dry cotton layer, then desiccant layer, then dry cotton layer. Once seeds are dry, they may even be packed in a plastic bag and stuffed in the bottom with a final layer of desiccant and O2 absorber. Actually I’m thinking O2 absorbers need to be on bottom. Next a final vacuum seal. Alternatively, if one had the equipment for vacuum packing in retort bags, I would think that would be a good method. The problem is that you can’t inspect the contents as you can with glass. So glass is the best method. Finally you could freeze or refrigerate the seeds in the glass containers or simply store them at ground temps away from light.
Opening the containers up year after year to get seeds from them for planting would expose them to new moisture and oxygen. So each time a new treatment process would be needed. I don’t know how to protect seeds with higher moisture content from fungus, except to say again keep them free of oxygen and air tight. Maybe its best to keep those vacuum sealed and at near freezing temps. It was mentioned that keeping seedlings at low light levels to be an option for seed banks, but that’s not a good option for us, I’d think. Seeds can be soaked in fungicide, as is done in agriculture, but then that is no longer organic, right? Seeds in agriculture are treated with fungicide and pesticides. No, at least right now, I think a vacuum or O2 absorption might be best for us.
In the end, the only way to see if we have been successful at storing seeds for a period of time is to plant them and see what kind of germination rate we achieved. I also read something about dormancy, where a seed could be good but dormant and I guess planting alone won’t bring them out of it. There is more than one way to bring seeds out dormancy, but one that was mentioned was soaking the seeds in a sulfuric acid solution. This is called Scarification. For example cracking a nut hull with a hammer slightly is a scarification process. Maybe simply soaking seeds overnight in water would help.