Can ALL seeds be refrigerated?

Sulphur, LA(Zone 9a)


I have been searching the forums for a few days now. I have seeds that I want to keep viable (save) for future use. I have been told by a MG in my area and a DG trader that they keep all of their seed in a freezer. I am not sure how safe this will be for seed that does not do well above zone 7. I am zone 9a.

My Question is can ALL flower, plant, veggie & herb seed be safely kept in frig? OR... is the freezer method the way to go?

I have kept all my seeds, so far in a extra large recipe box that my paw paw made for my maw maw's recipes. I have not had any problems with bug, weevils or the like. But I would like the pros of long-term storing viability.

Is there a hard n' fast rule maybe? Like all flower/plant seed zoned below 7 should be kept refrigerated.

Thanks, Kim

Everett, WA(Zone 8a)

I can't say for sure. Some seeds can't be dried out and stored - they must be used fresh. I guess they can't be frozen, because freezing wet tissue usually bursts cells.

Most seeds are "desiccation-tolerant". I also guess that any seed you can save for more than a few months are desiccation-tolerant. I just don't know if ALL of those are also freezer-tolerant.

For short-term storage, like 1-3 years or 1-5 years, freezing is not needed for most seeds.

I agree (from reading) that "many" seeds can be frozen, and will keep that way much longer than they would otherwise. Which ones can't be frozen? I don't know.

Here's one thread where someone says "any", then, "Except for tropicals that should stay moist and be fresh sown like citrus", then "Most people freezing seeds are doing it for edibles."

These guys seem knowledgable, but only say that "most" seeds will loast 40 years if dry & frozen. They also point out that plastic and Ziploc bags are NOT airtight.

Frost-free freeers will dessicate seeds (probably to death) over several years unless the seeds are sealed airtight. "Freezer burn". Seeds in a ziploc in a vegetable "crisper drawer" will gradually absorb humidity since the crisper is MORE humid that the rest of the fridge, not drier. I think: "double-bag them with dessicant in the fridge!" But many people don't, and still get some years of viability.

(I think that heat-seal "freezer bags" resist migration by oxygen and humidity a little better than Ziplocs. But a Mason jar IS airtight.)
- - - - -
Here is a very technical, scientific paper, but the author is really into ultra-dry, low oxygen stoage and says little about freezing. He thinks that (under some conditions like low oxygen), ultra-drying seeds to 1-3% water can extend their lifetime by a factor of 4 to 16! But he admits that "The debate might last for years until the subtle factors behind these opposite opinions are fully understood. "

- - - - -

Every site stresses DRY storage, and cool, and dark. If there's a way to measure it, the seeds should contain 5% to 7% water (by weight). That's probably around 30% relative humidity.

Many urge uniform coolness and humidity - avoid cycling up and down. Thus airtight storage should give you longer viability as long as it stays dry.

One site suggested that optimum humidity for long-term cool storage is 25-35%. Silica gel can keep a well-sealed jar drier than that, so I'm going to start using less silica gel in each jar.

If you don't freeze, optimum temperature may be the range from just above freezing to 40 or 45 F.

Sulphur, LA(Zone 9a)

Thanks RickCorey_WA,

I will read all 3 links provided. I am glad I checked further instead of just popping everything in the freezer. For now, I am going to put seeds in a jar w/ a small silica pkt. and keep just as I have; since I've not encountered a problem so far. I am not anticipating needing storage of most of the items for beyond 3 years. I'd prefer to safe than sorry.

I was thinking about the freezer method of storage especially for seeds of future food production. If the freezer/electricity should fail for a long period, wouldn't the seed be in danger of condensation creating humidity in the bags? I would think they would then have to be used in a very short amount of time? So maybe it's not the best method for storing seeds for long-term food production.

There's so much information out there and so many contradictory. Thank you for responding and for the links.

Everett, WA(Zone 8a)

You're very welcome.

>> There's so much information out there and so many contradictory.

I agree!

Please, if you find reliable information (or even more interesting opinions, please, share your discoveries here!

>> I am going to put seeds in a jar w/ a small silica pkt. and keep just as I have; since I've not encountered a problem so far.

That's exactly what I do now: store at room temp (or as cool as I can arrange without any risk of condensation) plus a little desiccant. I used to use a lot of desiccant, but that might be TOO dry.
The seeds are in 2x3" Ziplocs inside big plastic jars or tubs.

P.S. If the silica gel pkt has been exposed to air for more than a few days, it will be exhausted and won't do anything for you. They can only absorb X amount of humidity, then they need to be regenerated at 250 F for a few hours (no hotter). Or just buy a pound of flower-drying silica gel at a craft store for $5. Probably a teaspoon to a tablespoon will handle a quart to gallon sized jar IF it is AIRTIGHT. Any leak means that you'll need to replace the silica gel periodically.

There are pink/blue humidity indicating strips.

>> If the freezer/electricity should fail for a long period, wouldn't the seed be in danger of condensation creating humidity in the bags?

Here's my theory:

- In the freezer, they HAVE to be in a humidity-proof, air proof, water-proof container, or the freezer will "burn them" by pulling even more humidity out, drying them to death. Like a Mason jar, or a heat-sealed mylar bag.

- Since it is air-tight, what ever they are in will not care if humidity condenses on the outside, or melting ice covers them with water..

- They can't go into the freezer until they are really dry.
- So, when power fails, there won't be any humidity inside the jar to be ABLE to condense inside the jar.
- Also, they are SEALED and the power loss will RAISE raise the temperature.
- That actually lowers the relative humidity INside the jar, unless water leaks in.

- When you remove the jar out of the freezer to get a few pkts out, probably you should
- Wait until the whole jar warms up, wipe off the OUTside condensation, and then open it.
- All the seeds will come up to room temp, but you avoid trapping more condensation INside the jar.
- That what I did while storing pepper and tomato seeds in my fridge.
- Remove the jar, wait until warm, wipe it off, let i9f dry further, THEN take a small pkt out or add a pkt in.
- Temperature cycling is bad, but humidity is worse, and CONDENSATION is awful!

Central, TX(Zone 8b)

I'd vote for keeping seeds in the fridge, properly sealed (glassine envelopes) with desiccant packets inside a mason jar or some such moisture proof container. The freezer really isn't necessary unless you're going for really long term storage, and folks are correct - if the moisture content of the seeds and the temps in the freezer aren't just right the seed's embryo can be damaged or killed.

Everett, WA(Zone 8a)

Garden -Sass,

Everything I've read that comes from professionals says that your method is the best for several years storage.

"Dry" is crucial for stretching out their viability, so Mason jar plus desiccant is important.

After that, "steady cool" is important, so in-the-fridge is better than a varying room temperature like 60 to 75 F. Of course, avoiding condensation when you take them out is really crucial, so they have to warm up before you open the Mason jar.

Most sources also say that, if you need much longer storage, like longer than 5 years, frozen DRY seeds last longer than cool dry seeds.

And the techies point out that seeds in cryo-preservation, like liquid nitrogen temperatures, last even longer than frozen seeds.

I go crazy when people mention that they got fair germination from corn or peas that sat in a paper bag in an unheated shed for several years, or 5, or 10 ... I guess that works, too!

This message was edited Mar 1, 2013 4:45 PM

Central, TX(Zone 8b)


Regarding crazy...They may get them to germinate however one wonders if the resulting plants are productive compared to properly stored or fresh seeds.

FYI - I'm a fan of the Foxfire book series and the methods used to preserve seeds, vegetables, when and how they planted and they ways they tended their gardens...a living history of yeoman farming passed down through the generations in Appalachia. AND it's the source of my alias!!! Garden Sass is a mixed plate of fresh vegetables straight from the garden. Love garden history!

Everett, WA(Zone 8a)

When someone says they have a method that works, I assume they're right. But maybe there is some factor they didn't mention, that makes it work for them yet might not work to everyone's satisfaction.

Like they might be saving really, really hardy seeds.
Or they might always plant 3-4 times was many seeds as needed and thin out all but the most vigorous.
Or they might have constantly low humidity.

>> the Foxfire book series

I keep looking for inexpensive encyclopedias or recipe books from the 1700s and 18800s. There might be low tech, low-energy solutions for more problems than we think.

My favorite garden book is "The Complete Book of Garden Magic". The new-fangled second edition is from the 1950s, and the author is proud to have brought it up-to-date with all those scientific improvements.

I think its best lesson is that people in the 1940s knew very effective ways to garden - and they assumed that gardeners were willing and able to apply however much labor and time was needed.

This message was edited Mar 5, 2013 3:18 PM

Central, TX(Zone 8b)

Labor...yes, my ancestors had time to labor with the seasons and had to make use of animal power, their own muscle power and ability to think through solutions to whatever situation arose. Now most folks can just buy some machinery to do the muscle work!

I'm an avid collector of life experiences from the beginning of this country through the early 1900's; my bookcases can attest to that! Especially anything that relates to what we call gardening. Folklore and customs add spice to the mix. I've identified my ancestors and tracked their migration from western Europe to our east coast and beyond as the country grew. I've looked for their neighbors and accounts of their existence to help complete a picture of the life and times of my folks. It's a never ending search - thank goodness for the Internet!!!

CREZIERES, France(Zone 8a)

I recently had occasion to write to the technical department of the Millenium Seed Bank at Kew asking a similar question regarding loss of viability in 'swapped' seeds and how much benefit there was in refrigerating. The following is the response....
Dear Michael

Thanks very much for your e-mail and Im very pleased that you support our conservation aims.

Although storage temperature may be one reason for a loss in viability, its likely that this loss could be occurring at various stages in the process. The donors may be collecting seeds that have not yet reached maximum maturity, and thus will not have achieved maximum germinability, and/or may not tolerate drying. Alternatively they could have been collected past the point of maximum ripeness, when viability may have been lost under poor field conditions (e.g. high temp and high humidity) for a few weeks. Then as you say, the seeds could have been stored in sub-optimal conditions prior to despatch to the Seed Exchange (e.g. again high temps, high humidity).

When collecting seeds, either for long-term conservation or short-term, garden seed saving, the key activity is to reduce the moisture status of the collection. Having made a high quality collection from seeds at full maturity and at the point of natural dispersal (when they would normally be released from the plant), it is important to start drying the seeds immediately in order to maintain this quality. For every 10% reduction in relative humidity, seed storage life will double. You can carry out this drying over a bed of dried silica gel/rice/charcoal in a sealed container effectively a mini dry room! A humidity dial can be purchased for around 5 on the internet or in garden centres, and put inside the sealed container, to monitor the progress of the drying.

Once the seed collection has reached around 15% relative humidity (as shown on the humidity dial) the seeds can be sealed in a container (with minimum airspace try old film canisters, glass jars with screw lids, plastic containers with lids) and put into a fridge or freezer. The cooler you can get the seeds, the longer they will remain viable (for every 5C reduction in temp, storage life will double). The ultimate seed storage temperature is -20C but a domestic freezer at -18C will be fine.

The temperature in a freezer is likely to be a lot more consistent than room temperature over a few months and will make all the difference to the life of the seeds. Most households have a freezer running anyway, so this would not be an increased cost for the donors and strikes me as a very good idea you must stress the importance of drying seeds before putting them in the freezer however as if seeds are frozen with too much moisture, ice crystals will cause structural damage within the seed tissues.
The link for their technical data sheets is...

For my part, I think that, though no reference is made to tropicals, it would be sensible to divide seeds ofd tropicals in two - freeze half (after drying) and store the rest in a fridge. That way, any damage by freezing to the seed structure can be avoided while optimising the advantage of the cooler temperatures.

Hope this clarifies.

Jackson, MO(Zone 6b)

There's an article written by Tom Clothier that states he refrigerates seeds for a period of time, then takes them out of the refrigerator. He says he refrigerates all seeds except Gomphrena. I was researching Gomphrena seeds today, and his article popped up.

(For what it's worth) :)

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