Drying Seeds with Silica Gel

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Posted by @RickCorey on
It can be slow to dry seeds thoroughly in humid weather and prevent mold. Seal partly dried seeds in a tightly sealed jar with a desiccant like silica gel to get them down to 15% eRH, which will give them the longest possible viable lifetime in storage.

You can dry and store seeds in high humidity - even a monsoon - if you have tight-sealing jars and silica gel.

Put the seeds and/or the silica gel into paper envelopes. Humidity moves easily through paper.
Tape or staple them shut so you don't need to separate silica gel from seeds when you're done.

Now put both into a jar and seal it tightly. (You want to pull humidity out of the seeds, not the entire atmosphere.)

Stir them every day or two, so the seeds on the bottom are exposed to dry air.

That's all, except for the waiting.

Kew Royal Botanic Gardens post-harvest handling advice for seed collection:

Stored seed's viable life span approximately doubles for every 10% reduction in seed eRH.
("eRH" is equilibrium Relative Humidity.)

Seed collections should be dried to around 15% eRH for long-term conservation of orthodox seeds.
15% eRH works out to 4-7% moisture content (% water by weight), mostly depending on the seeds' oil content.

You can use less silica gel if you can get them mostly clean and mostly dry before you lock them up with the desiccant. At least remove stems and leaves and pod husks. I dry seed pods and flower heads in paper envelopes saved from bills, propped up in cereal boxes cut in half the long way. Dozens of varieties fit in the same space as 2-3 paper plates.

Silica gel desiccant can be bought from a craft store's flower-drying isle. $5-$7 for a pound or two.

And you can regenerate silica gel in a stove. Bake a shallow layer at 250 F for several hours, stirring it a few times. Seal it back in glass before it sucks up much humidity! 250 F will melt most plastics.

Silica gel is safer than sand - sand is crystalline silica, which can produce dust that is irritating or even cause silicosis if you breathe enough of it.

But silica gel is amorphous silica, which is even safer and less irritating than sand. It can't cause silicosis. It is approved by the FDA for use in food and pharmaceutical applications.

But don’t eat the humidity-indicating card! They use a little Cobalt Chloride.

If you want to get all scientific, put a blue-pink humidity-indicating card inside the jar, facing out so you can read it through the glass. Then you'll know when the silica gel is exhausted and you need to replace it with fresh desiccant. And you'll know when the RH (relative humidity) gets down to 15% and stays there.

Thumb of 2015-11-20/RickCorey/2eab6c

Or insert a slip of newsprint. If it is dry, it will be crisp and crackly when you open the jar to feel it.
If it is limp, your seeds are still trying to rot and will rot if you let them.

Drierite Relative Humidity cards at 40 cents each:

ULINE humidity cards, $50/250 3-spot cards or $70 / 400 6-spot cards

More seed-drying and seed-storing links:

https://garden.org/ideas/view/...... (silica gel for seed drying)
https://garden.org/ideas/view/...... (frugal uses for paper envelopes)
https://garden.org/blogs/view/... (poorly-formatted general desiccant info in "blog")

Kew Royal Botanic Gardens Technical Information Sheets about collecting and storing seeds,
written by Millennium Seed Bank staff.
Kew Millenium Seed Bank:

collecting seed in the field:

Comments and Discussion
Thread Title Last Reply Replies
Be Careful by DavidLMO Nov 24, 2015 12:06 AM 10
Fact- packed! by SRMc207 Nov 23, 2015 12:12 AM 1
Good info! by Weedwhacker Nov 20, 2015 9:13 PM 1

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