Will silica gel over-dry seeds ?

I'm finding contradictory information online. Some sources indicate that silica gel is good for drying seeds initially, but that if the seeds are left with the silica gel, they will over-dry them and the seeds won't sprout. Other sources talk about storing seed with silica gel.

I store my seeds in ziplock bags, because that way they can all fit in a tub, whereas glass jars would take up a lot more room. However, the ziplock bags are not moisture proof, especially since I have multiple paper packets in each bag and open them a lot. I thought that if I put a paper envelope with a few teaspoons of silica gel into each ziplock, I'd be able to keep them dryer; I'd replace the gel whenever it turned color.

What do you think?

I'd love for you to do the experiment. Put some seeds in a glass jar with way too much silica. Store some of the same seeds in other ways, and see which germinates better.

I wonder how long the alleged over-drying damage takes to manifest? Days? Weeks? Years?

Great question.  I found a product at a local big box called DampRid that should get down to 25%RH.  So I sealed off a shelf in a bookcase that I use to store seeds/beans/rice and put some DampRid in there.  It didn't dry the area out at all (per my remote indoor/outdoor thermometer).  So now I'm thinking about getting some silica gel to try.  

They do make a few kinds, one that color changes as it gets more "full".  I think there was some toxicity associated with that color changing agent so do your research before picking a gel...  Regardless, you can recharge silica by heating it in the oven to dry it back out.

From what I've learned in some seed saving classes, you want the temperature (F) plus the humidity percentage to be under 100 for good seed saving.  That's part of why I'm leaning towards making a "dry closet" to keep all my seeds in and monitor the overall humidity and temperature.  Then if it's getting too dry (if that's a problem) I can intervene.  Same could go for your tub.  Maybe put the silica in the tub instead of each seed ziplock and monitor it with a hygrometer?

Check out Carol Deppe's book ... Breed Your Own Vegetable Varieties.  Much of the info you are seeking will be there.

What an interesting idea with the silica gel! It's also good learn that the humidity and temperature should stay below 100F. I grow microgreens commercially (small business, but steady) and came across a good deal for sunflower seeds end of last year. So I bought 200 pounds of them. We live in a small house and don't have much extra space for much of anything, so I decided to store the seeds in the basement which is not finished but also not unfinished. I would call it a rough basement. It gets humid in the basement, about 75% -80%, but it also stays at a steady temperature year-round of about 60 degrees. I put the seeds in steel garbage cans and added diatomaceous earth to them, and closed the cover tightly. So far they are holding very well. I did the same with field peas. The way I was thinking was that the DE is very drying so would hopefully hold the humidity off the seeds, as well as, of course, the insects. It's only been a year so we will see how they continue to hold. I still have quite a bit of seed left down there.

I got some silica gel from hobby lobby today so I'll try it out and report back...

good question. I just popped kernels off the corn that I grew this year. some of it was moldy to greater and lesser degrees, fusarium and aspergillus?, pinks and blue/green.   the worst became bird food. I'm committed to planting it out again - I put a mixture of fireplace ash in with it.  Now that I've got more than i could plant out i should do a germination test.

I live in tropical Africa.  We have two rainy seasons.  We also have endemic malaria.  We get malaria like Americans get the common cold.  A couple years ago they came out with a handy little home malaria test.  Kinda looks like a home pregnancy test, but uses a drop of blood and a buffer solution.  Anyway! Each malaria test comes with a tiny packet of silica inside.  I have been saving those and throwing them in my saved jars of seed.  I never considered that over-drying might be a problem.  But so far, I have had good germination in everything except pigeon peas.

I don't think it is possible to over dry seeds without over heating them.  I know a guy that runs a survival seed business and discussed the research with him.  I don't remember the exact number, but he dries seeds to low single digit relative humidity.  He built a special cold dryer to do it.

I just germinated some seeds I had stored in plastic match containers with a small packet of silica for about 18 months.

Ok, I have an initial report from my silica gel experiment.  I sealed off a shelf in a bookcase with a piece of plywood over the front with weatherstripping.  I put a pint of silica gel in a wide mouth mason jar in there (no lid).  After two days the dew point was unchanged (I never opened the door).  I figured maybe I needed to expose more surface area so I poured half the silica into a cereal bowl and kept both the bowl and the mason jar on the shelf.  Three days later and the dew point is still unchanged.  

Maybe a physicist out there can tell me if I'm missing something...

I bought some unscented 100% silica cat litter to use as a dessicant, many grocery stores carry it. As another poster mentioned heat will dry out the silica beads and allow them to be reused, that is how the "rechargeable" small plugin dehumidifiers for gun cabinets/safes and the like work, the gel changes color, plug it in to heat it up and dry it out and it can be used countless times.

Also since no one has mentioned this, using desiccants will kill some of the shorter lived, more fragile seeds.

For purposes of storage, there are basically two types of seed: 'desiccation-tolerant' and 'desiccation-intolerant'. Most of the garden plants with which we are familiar produce desiccation-tolerant seeds, which means they can be safely dried for long-term storage. Exceptions include many aquatic plants, large-seeded plants, and some trees (such as oaks and buckeyes), many of which produce desiccation-intolerant seeds and will die if allowed to dry.

Desiccation-intolerant seeds do not enter dormancy after maturing. Instead, respiration and other physiological processes continue. Continued respiration after maturation causes desiccation-intolerant seeds to deteriorate rapidly once they have matured, so they must be planted while still fresh. Desiccation-intolerant seeds partially or completely lose viability if they are allowed to dry—usually they die.

Some seeds (such as citrus) are 'borderline' desiccation-intolerant. These can be dried and stored for some time, but lose viability quickly and germinate slowly once they've been dried.

http://howtosaveseeds.com/store.php