Seed Fermentation: Why and how to do it

I need a shirt that says, “I LOVE SEEDS.”

I have them everywhere. In envelopes, on pieces of parchment paper laying on the windowsill, in bowls…everywhere.

Being able to save seeds from one year to the next is pretty much the best part about growing heirloom fruits and vegetables. Your garden pretty much starts to sustain itself without the need to purchase any more seeds!

(Of course, if you want to buy new seeds just for the fun of trying a new variety, I’m not going to judge you. Ever.)

Saving seeds is pretty easy—scoop ’em out, let ’em dry, and store in a cool, dry place until next year. But there are several types of seeds that benefit from an equally easy process: fermentation.

By letting seeds ferment, you accomplish a few things that will help ensure better germination rates in the next season:

  • removal of the flesh and goo that can cover seeds, which can hinder germination
  • killing possible seed-borne bacteria that can prevent germination altogether

There are several vegetable seeds that benefit from fermentation, including tomatoes (both cherry and standard), cucumbers, and squash, all of which you’ll see below.

How to Ferment Seeds

Step 1: Remove seeds

It might be hard to do, but only take seeds from fruits or vegetables that are free of disease or damage. This helps ensure that your seeds are healthy.

tomato_fermentation 1-minFor tomatoes, cut the tomato in half. If it’s a Roma tomato, like mine, you might open it up to see no seeds at all! But don’t be fooled—fleshy tomatoes like Roma do have seeds. They’re just hiding under a flap of tomatoey goodness.






For cucumbers, I’d recommend slicing the fruit width-wise, rather than length-wise. When you slice them length-wise, you may slice many of the seeds in half, rendering them unsuitable for saving. You only want to save whole, mature seeds, like this one.





squash-fermenation 1-min

Squash seeds are very large, so they’re quite apparent. Just scoop them out and separate them from the innards, then toss them in a bowl.






Step 2: Add water and give them a stir

tomato_fermenation 3-min

Don’t worry about rinsing any of the seeds. Just put them in their own separate bowls, and add an inch or so of water, then stir with your finger.

Let the seeds sit for three days out of direct sunlight. Once or twice a day, give them another stir with your finger.

Step 3: Ignore the smell

They may start to stink, but that’s okay. In fact, that’s good! It means that they are, in fact, fermenting. Fermenting is a smelly process—for squash seeds in particular.

Step 4: Strain and dry

At the end of the fermentation process, the good seeds should have sunk to the bottom, and any bad seeds will be floating at the top. Pick out the bad seeds, then pour the remainder of the bowl through a very fine mesh strainer and rinse.

squash_fermentation 3-min

Spread seeds on paper towels or parchment paper—I prefer parchment paper, because the seeds won’t stick to it nearly as much. Let the seeds dry for 5-7 days. They need to be completely dry before you store them, otherwise they can mold or rot in storage.

Step 5: Store in a cool dry place until ready to plant

Store seeds preferably in a paper envelope (I use plain white coin envelopes that I can write notes on) or pretty much anything that isn’t airtight. You want them to be able to breathe. Write the name and variety of the seed (Ex: Tomato, Roma) on the outside, as well as the date they were harvested. This will help you keep track of what seeds are still good from year to year.

That’s it! Super simple, and greatly increases your chances of successful germination the next season.

Do you ferment your seeds a little differently? If so, tell me why! I’d love to know.


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