tomato seed fermentation

by Doug

Why - and how - do I ferment tomato seeds?

Mayo Underwood (an heirloom seed expert) wrote this explanation of tomato seed fermentation.

As always, if you have other questions, please add them in the comments section. :-)

Take it away Mayo.....


Why is fermentation better than drying seeds on a paper towel?

The gel sac around each tomato seed contains certain chemical compounds that inhibit germination until the tomato ripens, and may contain tomato diseases. In nature, the fruits fall off the plant and slowly rot. As they do, the natural fermentation process destroys the gel sac (including the growth inhibitors and any diseases) and allows the seeds to germinate when the right conditions are present, generally the following season. Saving tomato seeds by fermenting them is the way to mimic Mother Nature's fermentation process.

Here's how to do it:

Select the tomato(es) you like best (one variety at a time) and scoop out the seeds. Put the seeds in a jar or container with about twice as much water as the quantity of seeds in the jar. (e.g. 1 Tbsp seeds with 2-3 Tbsp water) Cover the container with its lid or with plastic wrap. (The cover is only so you don't have to smell the fermentation process - not a delightful experience.)

Keep the container at room temperature for several days. Put it where you'll see it and remember to stir or shake the contents twice a day. The seeds will ferment faster in a warmer room (80°F - 26°C for example) than in a cooler room (65°F- 18°C). You can often spot individual seeds moving as the "good" seeds sink to the bottom and the non-viable seeds and debris rise to the top.

In a few days, a layer of greyish-white mold forms on top of the water - a good sign. When that layer of mold covers the water's surface, fermentation is done. If you leave your seeds in the water beyond that point, they'll start to germinate, so be sure to check the jar often.

When fermentation is done, add more water to the jar
- about twice what was in the jar originally. Stir the contents very well, then let the container rest for a minute or two. Separation will occur again - with the good seeds settling at the bottom and more debris rising to the top. Gently pour off the top layer - and add more water. Stir and let rest again, then pour off the top layer. Repeat this process several times until all the debris is gone and only the good clean seeds remain.

Pour the clean seeds into a strainer. Let the strainer sit for a few minutes on a dishcloth or paper towel to absorb excess water, then spread the seeds to dry on a NON-porous surface - glass, ceramic, stainless steel, etc. They'll stick to a porous surface. You can also leave the seeds in the strainer to dry. Wherever they are (in a place with good air circulation, out of direct sun), stir the seeds around once a day or so. This exposes more seed surfaces to air, for more even drying, and also prevents clumping.

The drying process takes a few days. The more humidity, the longer it takes NO cheating, please....putting seeds in a microwave or food dehydrator or oven, even at a very low temperature, saps their fertility. Not good.

To test for dryness, bend the seed. If it breaks it's dry; if it only bends, let it dry further. If your fingers are too big to hold a seed and bend it, put it on a hard surface and press down on it with a fingernail, It if merely dents, it's not dry enough; if it breaks, it's dry. If you're not sure, let the seeds dry for an additional day or two. There's not too much worry about over-drying seeds.

When the seeds are dry, store them properly.

When properly fermented and stored, tomato seeds can last 5-10 years. As a bonus, seeds dried in this manner germinate in just a few days, especially in the first year or 2 when they're very fresh. They diminish a bit in viability each successive year.

Comments for tomato seed fermentation

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by: Bobby

I was reading up on tomatoes and kept coming across "fermenting (your) seeds" so I looked it up and found your process. I've been growing tomatoes from my own seeds for years and I usually just rub the seeds between two paper towels until the jelly sac is sloughed off and absorbed. Then I simply pick out the seeds, wrap them in a dry paper towel, let them sit for a couple days, then stick them in a ziploc baggie(still wrapped in the paper towel).

seed tapes
by: Anonymous

I read somewhere that it was best to use white tissue paper (the thin gift wrapping type) for your paper and to make a 'glue' from wheat flour and water to attach them to the paper. I had planned on trying that with radishes this spring but never got around to following thru other than actually getting all the stuff to do it. I suppose that the flour glue dissolves whereas regular 'Elmer's' type glue wouldn't and would just preserve the seeds forever encased in it.

making your own seed tape
by: Cheryl

Doug, I have been gardening for years, but I learn something new everytime I visit your site!!!

I have read somewhere that if you want to make your own 'seed tape', that you dry the seeds in place, properly spaced on paper towels; will this hurt the seeds in any way, if done after fermenting, then storing on the paper towel strips until next season?

Thanks Mayo, wonderfully written explaination of tomatoe seed saving, , easy to understand!

Doug, thanks for involving Mayo!

Duh...what's properly stored mean?
by: Anonymous

Oooo! Kathie has a wonderful idea...and she sounds so organized...okay...that deserves a raspbery for that! ;-p Mayo that was one terrific job of explaining! Until...until you got to the part about storing the seeds properly. Duh, what does that mean? Remember, you are speaking to the seed saving challenged here...VBG. Now I wish I had saved the seeds of some of the tomatoes that I have already eaten that were absolutely WONDERFUL flavor-wise. Oh well, you can bet I'll be on the lookout from now on! And that was anothergood question...are their any other seeds that need to be fermented like the tomatoe seeds? Naturally, I could do without the anticipated wonderful aroma but there's no gain without a little pain is there? Thanks bunches!

Storing seeds
by: Kathie

I hope I am doing it correctly! I take a digital photo of the tomato, flower, or what ever, shrink it to a 4x4, print it out on regular white paper, and make a pouch for the seeds. Then I store them in a plastic bin in a cool dark room.

by: Anonymous

thank you for the great article what about storing seeds properly and how about other types of seeds.

Very Thorough
by: Heather B.

Thanks for the article. I've always wondered how, and this was very thorough and easy to understand!

store them properly?
by: Annette

I have always heard that it is proper to store left over seeds in the refrigerator, but should they be in a sealed container. Will a pill bottle work or a sandwich baggie? Maybe you could explain "properly" in another blog.
Many thanks

storing seeds
by: Shirley

Great explanation for fermentation! Thanks. Any other seeds need to be fermented? I assume storing seeds properly is in a dark dry place. Is there any advantage to freezing them?

Proper Storage
by: June

Hi Mayo,
Nice job! I have only 1 question, and a thank-you for the info.
My idea of "stored properly" is in a sealed envelope in a large plastic storage bag (with other envelopes) in my refridgerator. Not the crisper section. Is that your idea of stored properly?
thx again

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