Garden of Eatin' / Seeds & Seedlings

The Power of Fermenting and Saving Tomato Seeds

The power of fermenting and saving tomato seeds

I’ve talked about fermentation quite a bit on this blog, from fermenting your cabbage to fermenting your chicken feed.

But fermenting tomato seeds?

Yes, it’s a thing, and I’ll show you the best way to save tomato seeds and increase germination rates by adding this one simple step to your seed-saving routine.

Tomato seeds drying on a white plate

First, what is fermentation?

In a nutshell, fermentation is the process of good bacteria breaking down the structure of your food so they become more bioavailable.

Why is this important? Because even if you have the healthiest diet in the world, you aren’t “what you eat,” per se, you’re what you digest and absorb. Having your food more bioavailable means you’re getting more of the vitamins, minerals, and phytonutrients out of them.

When it comes to fermenting chicken feed, for instance, lacto-fermentation reduces the anti-nutrients found in the outer layers of grains, seeds, and legumes, making the food more digestible for your chickens.

Anti-nutrients are natural compounds found in most types of whole foods (including nuts, vegetables, and fruits) and various parts of plants (including roots, leaves, and seeds) that protect them from predators.

Close-up of tomato leaves in the garden

Since they can’t run or hide from danger, plants have much subtler defenses that can kill or weaken their enemies.

One of these strategies is producing anti-nutrients to guard against bacteria, fungi, insects, animals, and even humans. The anti-nutrients lock up the nutrition of a plant in a way that our digestive systems can’t break down, essentially “starving” us of certain nutrients.

Seeds, in particular, contain anti-nutrients as a fail-safe from being eaten before they can germinate and produce the next generation of plants.

That means every seed you save from your plants comes with a built-in survival mechanism that helps keep it viable until the proper growing conditions are present.

Read more: How to Soak Seeds and Speed Up Germination Time

This is especially true of “wet” seeds from tomatoes (as well as cucumbers, melons, and squash), which are covered with an extra protective layer on the seed coat that inhibits germination.

Worth a read: From Seed to Seedling: An Anatomy Lesson

To speed things along in the garden, tomato seeds benefit from the simple process of lacto-fermentation before you store (and eventually sow) them.

Overhead shot of tomato seeds scooped out into a jar

How does fermentation help with tomato seeds?

In the outside world, tomato seeds naturally ferment when over-ripe tomatoes drop from their vines and rot in the ground. The seeds sit in the soil where bacteria are actively working, waiting for days, weeks, or even a whole year for just the right environmental conditions before they sprout.

This is why it sometimes seems like tomatoes germinate best when we have nothing to do with it! They happily volunteer all over the yard, displaced from undigested compost or random bird droppings.

We can mimic this natural process by fermenting the seeds ourselves when we collect them from the fruits.

Lacto-fermentation removes the germination-inhibiting substance on the seed coat, that gooey gel sac that surrounds each seed. Fermenting also kills certain seed-borne diseases (as good bacteria overtake bad bacteria), which helps promote the health of seedlings and the vigor of mature plants.

During fermentation, bad seeds generally float to the surface of the water while good, viable seeds sink to the bottom.

It has also been said that properly fermented, washed, dried, and stored tomato seeds can last up to 10 years! Talk about passing down a true heirloom to your kids.

Related: The Stories Behind Heirloom Seeds

Side view of tomato seeds covered with water in a jar

Do you need to ferment tomato seeds to make them viable?

In case you’re wondering, no, you don’t need to ferment tomato seeds.

Non-fermented seeds have sprouted just fine for me… and they also have not. Often, it’s a matter of luck, timing, and genetics.

You can save tomato seeds the same way you’d save other wet seeds by rinsing and drying them, and leave the fermenting out of it completely.

But… If you can increase your chances of germination, have it happen much sooner in less than ideal conditions, and improve the health of your future plants, fermentation is too easy not to try.

Slices of tomato showing seeds and pulp inside

How to ferment and save tomato seeds

To begin fermenting, squeeze or scoop the seeds (with accompanying gooey stuff) out of fully ripe tomatoes into a clean, small jar. There’s no need to separate the seeds, but do try to remove as much of the pulp as possible.

Tomato seeds fermenting in a jar

Cover the seeds completely with at least an inch of dechlorinated (or filtered) water and loosely place a lid over the jar while the whole thing is brewing.

Do not seal the jar tight, as you want to leave some airflow for the fermentation gases to escape.

Tomato seeds covered with water to begin the process of fermentation
Tomato seeds going through fermentation in a jar
A lidded jar holding tomato seeds while they're fermenting in water

Within a day or two (more or less, depending on your ambient room temperature; warmer temps move the fermentation along quickly), a frothy white film will start to form on the surface of the water. It will smell slightly sour, like yogurt.

A layer of kahm yeast covering the surface of the water in a jar

The cloudy white film isn’t mold; it’s harmless kahm yeast, a common indicator of lacto-fermentation in action.

While it doesn’t look like anything significant is happening, it’s also a sign of your potential new seedlings and next year’s salsa.

Once the white film has covered the whole surface (in another day or so), it’s time to wash away all that scum.

Kahm yeast covering tomato seeds in a jar as fermentation progresses

Quickly pour off the top layer of water (with the frothy stuff and bad seeds) so all that remain are your good seeds sunk at the bottom.

Wash the seeds as you normally would, under gently running water in a fine mesh sieve. You can firmly but carefully rub the seeds against the mesh to remove any sticky remnants.

Tomato seeds being washed in a fine mesh sieve

Spread the seeds out on a paper towel and pat them down to absorb most of the moisture, then transfer to a non-porous surface (like a small plate) to finish drying completely.

Tomato seeds spread out on a white dish to dry

After a few days, store the seeds in a labeled and dated envelope in a cool, dark, and dry place. Your seeds are now ready for planting!

Want to save more vegetable and herb seeds from the garden? Check out my beginner’s guide on saving and storing seeds.

How to Ferment and Save Tomato Seeds

A lidded jar holding tomato seeds while they're fermenting in water

Learn how to save tomato seeds and boost your chances of germination by adding this one simple step to your seed-saving routine: fermenting tomato seeds.

Prep Time 5 minutes
Active Time 3 days
Additional Time 3 days
Total Time 6 days 5 minutes
Difficulty Easy

Materials

  • Fully ripe tomatoes

Tools

  • Small jar
  • Fine mesh strainer
  • Paper towel
  • Small plate
  • Small envelope

Instructions

  1. Squeeze or scoop the seeds (with accompanying gooey stuff) out of fully ripe tomatoes into a clean, small jar. There's no need to separate the seeds, but do try to remove as much of the pulp as possible.
  2. Cover the seeds completely with at least an inch of dechlorinated (or filtered) water and loosely place a lid over the jar. Do not seal the jar tight, as you want to leave some airflow for the fermentation gases to escape.
  3. Within a day or two (more or less, depending on your ambient room temperature; warmer temps move the fermentation along quickly), a frothy white film will start to form on the surface of the water. It will smell slightly sour, like yogurt.
  4. Once the white film has covered the whole surface (in another day or so), it's time to wash away all that scum.
  5. Quickly pour off the top layer of water (with the frothy stuff and bad seeds) so all that remain are your good seeds sunk at the bottom.
  6. Wash the seeds as you normally would, under gently running water in a fine mesh sieve. You can firmly but carefully rub the seeds against the mesh to remove any sticky remnants.
  7. Spread the seeds out on a paper towel and pat them down to absorb most of the moisture, then transfer to a non-porous surface (like a small plate) to finish drying completely.
  8. After a few days, store the seeds in a labeled and dated envelope in a cool, dark, and dry place.

Did you make this project?

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This post updated from an article that originally appeared on September 11, 2013.

Growing Tomatoes From Start to Finish

Linda Ly About Author

I'm a plant lover, passionate road-tripper, and cookbook author whose expert advice and bestselling books have been featured in TIME, Outside, HGTV, and Food & Wine. The No-Waste Vegetable Cookbook is my latest book. Garden Betty is where I write about modern homesteading, farm-to-table cooking, and outdoor adventuring — all that encompass a life well-lived outdoors. After all, the secret to a good life is... Read more »