Thanks for everyone’s comments. Here is the updated version of the file. I encourage you to make more comments below if you have further suggestions.
Seed Storage Guide.pdf (59.0 KB)
Could be great to mention how long they need to be air dried. And a chart for how long each kind of seed can be stored under different conditions (could be for example room temperature; fridge; freezer.
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Full text of the google document open for comments is below in case anyone can’t use that app:
Guide to Seed Storage
Types of seeds
The majority of crops produce seeds that go dormant when their moisture content falls low enough. The seeds of some species die when desiccated (many fruit trees like citrus behave this way). Either way, the natural lifespan of seeds of different species varies widely, from a single season to centuries.
With proper storage, the viability of seeds can be extended.
With improper storage, an entire seed collection can be destroyed overnight.
Primary Principles
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Moisture.
Most seeds go deeper into dormancy as moisture levels decrease. Thoroughly dried seed may be a bit slower to germinate as a result. Fluctuating humidity levels can lower seed viability. -
Temperature
Seed metabolism slows down at lower temperatures (though some species are unable to survive freezing, especially if they have high moisture levels). Generally the lifespan of seed halves every time the temperature increases by ten degrees Celsius. Fluctuating temperature also lowers viability. -
Pests and diseases
Seeds in storage are vulnerable to attacks from a wide variety of insects. Many species of beetles specialise in particular crops.
If humidity and levels are high enough then fungi can also rapidly destroy seed. -
Managing Moisture
Wet processing
Seeds from a few species (mostly cucurbits and solanums) need to be separated from gelatinous pulp which contains germination inhibitors by fermentation. The seed pulp is extracted, mixed with water and allowed to ferment for a few days. Timing depends heavily on temperature. If you are unsure you can ferment separate small batches, each for a different number of days, then test germination separately. Generally, the shortest period of fermentation time that gives clean but well-formed seed when the mixture is filtered and washed works the best.
The damp, washed seed is then spread on paper to air dry. I find newspaper works well since it doesn’t cling to the seed on drying. Stirring the seed gently as it dries can also minimise sticking. Once the seed is dry to the touch proceed to the next phase.
Air drying
The majority of crops produce dry seed which can be processed by hand (or using sieves/winnowing on larger scales) to remove any unwanted plant material.
Air drying is made more effective by increasing the surface area and enhancing airflow. Avoid heating the seed as this can rapidly lower viability. Spreading the seed out on trays in a cool, airy part of the house is often effective. Lining the trays with absorbent material (like a dry dishrag or paper towel) can help wick moisture away. If the seed is piled up, stirring it occasionally is advised. During unusually damp weather it can be useful to store the trays on top of the refrigerator due to the gentle warmth from the motor. Hanging seedheads up also allows water vapour to fall away.
If you live in an arid climate (or are processing seeds during a dry season) then it is often possible to prepare seed for storage by air drying alone.
Desiccants
After air drying seed may appear dry to the touch, only to release condensation once stored in a sealed container, leading to mold destroying the batch. If you can’t risk losing the seed, then using a drying agent can greatly increase your chance of success.
A range of substances can serve this purpose:
A. Silica gel- available in a wide range of forms. Can often be recharged by heating in a dry oven. Some forms undergo a colour change to indicate when they need to be dried again.
B. Epsom salts - a cheaper option for bulk seed storage, though a little less convenient. Usually sold as a clear form which is already saturated by water. After heating in a dry oven the Epsom salts turn to a white mass which absorbs large amounts of water vapor. Dry salt can be broken into durable plates for easy handling and reuse. Can be dried again but loses effectiveness before it turns clear again.
C. Wood ash- fresh wood ash is the cheapest/lowest technology desiccant. Limited capacity to absorb moisture but acts directly to stop pests and molds if mixed with dried seed. Traditionally used to protect stored seeds in many pre-industrial societies. Effectiveness varies with the type of plant material burnt to create the ash.
Fresh seed can be stored for a few weeks or months in a sealed container with a large amount of fresh desiccant, before being moved to another sealed container with a reserve of desiccant for longer-term storage.
Recharging your desiccant twice a year can be a useful routine to establish.
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Tempering Temperature
Seed can be stored in the vegetable crisper of the refrigerator to extend viability. This space is usually limited (and may cause conflict with other people). Often it can be best used to store small quantities of high-quality seed as a backup in case of disaster. Storing seed in the freezer presents similar issues at a higher level of intensity, so choose which samples to prioritise carefully. Generally, a balance of imported seed that would be difficult to replace and your own best seed as an emergency backup.
Refrigerators routinely fail. Fluctuations in temperature generally damage viability, but occasional warming periods shouldn’t be fatal. Storing seed in fridge doors is inadvisable for this reason.
Once you begin producing your own seed it is likely you will run out of refrigerated space. The next best option is a location that is generally cool and does not experience large temperature fluctuations. Avoid western exterior walls for this reason. -
Preventing Pests
Controlling moisture levels in stored seed goes a long way to making them unappealing to fungi and insects. No sane amount of fungicide will stop damp seed from surviving. Insect infestations generally damage damp seed more rapidly than dry. Warmer temperatures also favour both insects and fungi.
The types of containers used influence pest management.
Growers use a variety of solutions:
A. Ziplock bags- cheap, lightweight, flexible, and easy to label. Easy to bundle multiple bags inside another bag for limited organisation. Somewhat permeable to moisture, so need to be stored inside a stronger air-tight container. Good visibility for quick inspection. Poor pest barrier- many beetles will chew their way out. Applying a contact insecticide inside the larger storage container can slow infestations from chewing into other packets. Rodents easily chew through plastic.
B. Paper bags- cheap, lightweight, and easy to label. Poor visibility. Easy to tear. Very porous to moisture, difficult to seal to prevent pest spread. Best used for temporary storage during initial drying with desiccant.
C. PET drink bottles (“soda bottles”)- cheap, lightweight. Good visibility. Need the right type of pen to label. Relatively easy to store at high density. Very impermeable to moisture and pests. A little tricky to get seed into (need a funnel, limits desiccator options). Ideal for bulk seed.
D. Polypropylene/polyethylene storage boxes- decent visibility. Larger capacity. Variable seal quality. Useful as desiccator drying chambers or for bulk storage of ziplock bags.
E. Glass jars- heavy, fragile, and difficult to label. Good visibility. Variable packing density (depends on the range of sizes). Highly impermeable to moisture/pests.
F. Ceramic vessels- preindustrial choice. Heavy, fragile, no visibility. Highly impermeable to pests and moisture.
G. Gourds- traditional choice. Fairly durable, no visibility. Difficult to seal depending on shape and cut. Moderately permeable to moisture and pests.
Seed Store Routines
It is advisable to go through your entire seed collection once or twice a year. Be sure to let refrigerated samples reach room temperature before opening packets since moisture can condense inside. Desiccant should be recharged by heating in an oven once or twice a year.
Check every packet for signs of pests. Infested seed that you wish to keep should be frozen or given a pesticide treatment then stored separately. Avoid opening infested samples around the rest of the collection to limit spread of spores and insects. Discard old samples if they are no longer needed and space is limited.
All seed packets should be labelled with the species and date of collection or storage at a minimum. For containers that are difficult to label on the outside, you can write the details on a piece of paper or cardboard to place inside. Another alternative is to record sample details in a dedicated notebook or computer file and only attach coded labels to each sample.
Breeding for seed storage
Different crop species vary wildly in their natural longevity. Parsnip seed are reputed to have the shortest viability, with carrots close behind.
How easily seed can be stored under your local conditions is yet another factor to consider when choosing and breeding crops.
Conclusion
Most amateur crop breeders eventually end up overrun with stored seed. This usually happens first when they gather together seed from multiple outside sources. Bundling seed of the same species together in ziplock bags can make this stage easier to manage.
The second hurdle comes when they first start producing their own seed in decent quantities. After all the work of growing the crop and processing the seed it is common for their storage techniques to cause a minor disaster.
Learning to split your seed into different batches and experimenting with different processing and storage methods is a useful strategy to avoid losing all your hard work due to one mistake.
Storing all your seed in the same location creates a significant risk of catastrophe. Separating smaller samples of your seed to store in the refrigerator or freezer can make best use of this limited space. Sharing seed with trusted friends is ultimately the best insurance policy.
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I think sometimes that the issue of seed storage gets overcomplicated. There may certainly be exceptions depending on conditions, but I have never had problems just by following the most basic rules.
1- Make sure your seeds are completely dry. A simple test for squash and the like is if it bends instead of snaps, it isn’t ready. For corn or beans, hit one with a hammer, if it squashes instead of shatters, it isn’t ready. These are old time techniques that have always worked just fine for me.
2- Once they are dry, seal them up in something that will keep them dry even if you submerged it in water.
3- Put it someplace in the dark and keep them as consistently cool as possible.
Where I live it can be and often is quite humid. I often keep seeds that are dry enough to be safe from molds in paper sacks or cardboard boxes until the first days cool enough to put a fire in the wood stove at which time humidity in the house goes way, way down. Then I seal them in their containers and that’s all I’ve even needed to do. Even that isn’t always necessary as sometimes a stretch of days with low humidity is all that’s needed.
Seeds just aren’t quite as wimpy and fragile as sometimes believed, or at least that’s been my experience.
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To Mark’s comment about what did native people do I wonder the same. My question is how did native people dry their seeds in high humidity areas. Did they use fire, the sun, did they leave the germination inhibitors on or did they ferment? I want my method to be close to what they did, because it oughta be simple.
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I’ll include these useful tips in the document. Thanks!
People in cooler/drier climates definitely have a much easier job storing seed (especially doing it well enough to last multiple seasons). Once you know what you are doing you can often just run your fingers through a batch and feel if it is dry enough by the way it moves, but for beginners it is very easy to seal seed up which hasn’t released all its moisture yet.
If you are only storing seed for one season you can often get away with leaving it in open containers, or hanging from unprocessed seed heads if they don’t shatter too easily. I might include that option as well.
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Ill try to make it clear that it is normally straight forward for people in cool/dry climates. I just know from experience a lot of newbies put their processed seed into a sealed container before it is dry enough and lose the lot, which can be very discouraging when you are just starting out and thought you were getting somewhere.
I wonder too how much they would’ve planted wet fruits to come up whenever they were ready the next spring. So many talk about volunteer plants but that would be like mimicking how volunteers work right?
Yeah, I’ve made that mistake, too. My air is definitely dry enough (usually 0% humidity), but sometimes I have harvested seeds that are still a bit damp on the plant so that the pods wouldn’t shatter. If I put those into a plastic bag immediately, even if they look dry, mold forms. That’s happened to me a few times.
Now I’m trying to remember to leave any seeds I harvest sitting out on a plate for a week or so before putting them in plastic. Ideally, that will mean no more mold growing.
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REally good information. Could you include a header ir a footer on your document with you as the preparer and any references used so we can continue to research seed saving and credit your presentation? Would it be productive to show references for long term storage of each species? What is our goal? A few years or decades?
Some plants must be grown out every few years for seed to be viable so my growing schedule has to build in a timetable so seed viability isnt lost.
Maybe its also a landrace selection criteria to have long term storage abilit!y of the seeds, ten years or more?
I’m also curious if the seed coat endophytes are preserved or lost depending on seed storage technique and technology…
Im just trying to determine what does best inside clay pots and what seeds store best in glass or plastic?
Is there a seed storage container besides an old freezer that works better to provide a safe environment for the seed?
And will we assign several “backup” seed storage locations? Long term stewards?
We start with swarms, then a grex, then the landrace…should we be labeling?
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All great questions. I wrote it from my own experience, but happy to link to any good online references about seed storage (though link rot is always an issues). A list of suitable pest proof containers for keeping seed safe could be useful. I store mine inside the house so vermin isn’t an issue, but I know some other people use metal boxes or like you said an old chest freezer/etc which evens out temperature fluctuations even if it isn’t turned on.
I think somewhere I mentioned about the possibility of selecting for storage longevity, though it would be a very long term project since the time between generations could be very long (or maybe you could select for tolerance of poor storage conditions to speed things up). Some seeds I keep like Canna need no special storage- just an open bowl exposed to whatever pests and vermin come along and they will still remain viable for decades (though these type of seeds have very heavy seed coats and need hot water treatment to induce germination). There are structural trade offs between seed storage longevity and ease of germination in some cases.
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I believe fire was a major tool for seed preservation. Keeping seed near a smoky fire can keep them dry and repel weevils. I also remember hearing them storing seed inside gourds or clay pots in dry wood ash.
I totally agree that you can select for easily storable seed. I think this happens inadvertently even if you don’t mean to do it, but some species and strains seem to be easier to store just sitting around in buckets than others.
I will try to incorporate your ideas into the document next time I give it a once over.
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The oldest caches of seed found in Central Appalachia have been in rock shelters and caves. Containers have included woven and fabric types. Those are just the ones that have been found intact, it may not represent the most common forms of storage.
This ethnobotany and archaeology blog has helped me try to imagine how the prehistoric crops of the Eastern Agricultural. Complex might have been grown. I wish Dr. Mueller was still updating it. https://ngmueller.net/
I read some articles last winter that point to new evidence showing that one of the primary factors influencing seed longevity might be something most people haven’t taken into account before: oxidation. The presence of oxygen speeds up life processes in seeds and the relative lack of oxygen slows them down. It is pretty straight forward to limit the available oxygen around seed:
- Use glass jars with rubber sealing. These have shown to introduce the least oxygen into the container. Jam jars are the second best option.
- For long-term storage, limit the available oxygen inside the container by choosing a fitting size for the given seed. More air in the container means more oxygen needs to be eaten by the seed first.
Read more here: Groot, S. P., de Groot, L., Kodde, J., & van Treuren, R. (2015). Prolonging the longevity of ex situ conserved seeds by storage under anoxia. Plant Genetic Resources, 13(1), 18-26.
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