how to save seeds of heirloom tomatoes

I’VE ALWAYS JUST SMEARED the seedy innards of heirloom tomatoes on paper toweling, let them dry, and then stored them for the coming year–maybe rinsing the stuff in a strainer first, maybe not. That’s how to save tomato seeds the easy way. But fermenting the goopy gel and juice first for a few days offers some important benefits: The process may reduce some seed-borne diseases, and it also breaks down a germination-inhibitor in the gelatinous matter around the seed. (It also smells really bad, so pick your location wisely!) The story:

Like everything in gardening—a pursuit I always remind myself is part art, part science—experts differ on just how to save tomato seed. I’ve listed links to some variations below. But basically, here’s the idea:

1. Working with one variety at a time, select fully mature fruits to collect your seed from. The fruits you use should be true to type for that variety—not the runts, and not oddities like double fruit. Seed Savers Exchange says to avoid the first fruit from large-fruited varieties, too.

Suggestion: If you’re going to save a lot of tomato seed, plan to do this when you are making soup or sauce or maybe gazpacho, because there will be lots of tomato flesh that would otherwise go to waste.

2. Simply cut the fruits in half or quarters, then squeeze the insides—juice, gel, seeds, pulp—into a wide-mouth container. With large fruits, prevent splatter from going everywhere by using a bowl to catch the innards, then pour the results into jars.

3. Whether to add water to the expressed materials is a subject of disagreement. I don’t—but in the case of the variety up top, of which I had just one big fruit shared by a friend—it would have made the process easier. If you do add water, don’t use more than  the amount of tomato innards that you have.

4. Cover the jar with a piece of paper toweling and an elastic band to keep insects out. Again, this process really stinks, and will attract them.

Allow to ferment for several days in a spot that’s ideally “room temperature,” but not more than 70 degrees F. But hey, it’s usually summer when you do this, so temperature control is tricky. Avoid cooking the stuff in a hot, sunny spot! The garage might work, and spare you the funky fumes.

5. Shake or stir the jars daily, though some people also skim off the foam each day, some wait till three to five days have elapsed and do it just once. Hollow, non-viable seeds will supposedly float upward in the process, so you’ll be eliminating dead seed, too–or so some experts say.

6. After about four days, skim off and discard the fermented, foamy mess on top, then pour the remainder through a strainer and rinse thoroughly. Let excess water drain off; maybe give the strainer a few thumps in the counter to help.

7. Spread seeds onto paper plates that are labeled by variety. Don’t use plastic or glass or china plates; you want to wick excess moisture away from the seed, meaning paper is the better choice.  Allow to air dry thoroughly, which will take several weeks, before storing.

ALL OF THIS ASSUMES you are saving heirloom varieties—not hybrids, which won’t “come true” from their own seed. It also assumes that your plants didn’t experience any cross-pollination that would taint their seed.

Cross-pollination between modern tomato varieties seldom occurs,” says Seed Savers Exchange, “except in potato-leaf varieties [such as ‘Brandywine,’ ‘Stupice,’ or ‘Pruden’s Purple’] which should be separated by the length of the garden.” Estimates of how far that is range from 25 to 50 feet or more. Like so much else in this gardening business, apparently it’s a matter of opinion.

how the experts save seed:


  1. kristi says:

    Glad you shared the easy way, too. I have the best intentions of doing it “right” one of these days, but the easy way fits into my to-do list so much better. Now that I realize I should be seed saving while I’m saucing, I will make the extra effort.

  2. TeriKWeaver says:

    Perfect timing! My friend gave me a couple of giant Italian plum tomatoes this weekend, legendary for their odd shapes and their mode of transportation: they were allegedly smuggled into America a few decades ago in a bra.

  3. Virginia says:

    Our tomatoes are harvested already but I’ll definitely have to try this next year. We’ve had some success this year with peas and radish seeds so I would like to build on that going forward. Thanks for posting!

  4. Heidi says:

    I have been researching seed-saving in general for a presentation at my garden club. There’s conflicting advice on the best way to do some of those steps. For instance, I have read that the whole bit about seeds floating is not accurate, and in fact in a test floaters had the same germination rate as sinkers. I have also read to not use paper because they can stick to the plate. I use a window screen stapled to a piece of wood. Do not let them dry in sun, but do use a fan to help with the drying process. Tomatoes are fairly easy plants to save seeds from and don’t cross pollinate as readily as veggies like squash or corn, but older varieties have pistils which protrude from the corolla and may tend to cross. I think isolation distance for each variety is as simple as a tall crop planted between varieties.

  5. Great tips! Have you ever try to cross breed tomatoes to see if you can come up with your own hybrid variety? Not a traditional heirloom I know, but still fascinating to see what you may come up with. I am not talking about genetically modifying the seeds, simply a cross pollination.

  6. Ms. Becky says:

    I just tried doing this a few weeks ago but I’m going to try it again today. The mixture wouldn’t ferment, even after a week of sitting there on the counter top. I suspect that I added water to the mix, I cannot recall now, but I’m certain that I didn’t have a pulpy mixture as you describe. I always purchase four Brandywine plants each year and for the past couple of years only one of the four has been true to seed. I’m not sure what happens, but the garden center where I purchase my plants is reputable. I’m relying on my own seed next year and starting my plants indoors. Thanks for the clarity.

  7. Margaux Drake says:

    You my dear have exceptional timing as always! I just happen to have half of a to-soft-to-eat heirloom tomato in my refrigerator right now that a friend gifted to me, just perfect for the technique you suggested above. I’ve already dried some seeds in my dehydrator on low, but I will try this method too and see which seeds are better next year. We learn as we GROW!!! XO

  8. TeriKWeaver says:

    My seed concoction isn’t foaming or getting funky, and it’s been three days. Any thoughts? It’s in the house, in a well-lit room but out of direct light. Same temp as outside for the past few days, in the sixties.

  9. Tammie says:

    Two summers ago, I took some of my pitiful tomato harvest to the local feed and seed store and asked what I was doing wrong. The lady behind the counter asked one question – “Are you watering with city water?” – meaning water that has been treated with chlorine and other chemicals. Of course, I was! She explained that chlorine kills many of the helpful organisms which live in the soil, and it causes fruiting plants to produce hard, knotty, tasteless fruit. Since then, I’ve either aerated water in buckets or used an inline water filter, and my plants are looking healthier than ever!

    I wonder if this is the root problem for those commenters who could not get their tomato seed solution to ferment properly. If they have added chlorinated water to their mix, it could be killing the fermentation process.

    1. Flexy says:

      The issue with chlorine in tap water applies when you grow organically, since growing organically depends on the microorganisms. When you grow in hydro, like I started now, non-organic, it doesn’t matter whether chlorine is in the water. You want your growing environment actually as sterile as possible, so chlorine is even “good”. Otherwise, having sitting a bucket w/ water out for 24hrs gets rid of chlorine. Aeration as you mention works too. Whether the chlorine in the tap water prohibits the fermentation of the seeds, I will see. Possible. I am trying to save seeds from very tiny dwarf tomatoes, so I had to add some water. If this won’t wok I will try without water next time.

  10. Vicki says:

    I grow both heirloom tomatoes along with some hybrids. Can I get true seeds from my heirlooms or will they cross pollinate with the hybrid. My 2nd year with my heirloom seeds I saved was a failure.

    1. seminte de rosii says:

      As far as I know tomato cross pollination happens very rare. The failure about you mention is a result of another thing.

    2. margaret says:

      Hi, Vicki. Most modern varieties sort of protect themselves from crossing with neighbors, and the suggested “isolation distance” in the garden or field to maintain genetic purity is just 20 feet minimum, while the minimum for heirlooms and potato-leaf varieties is 160 to 320 feet minimum, and for the wildest types, the currant types, double that again. (Numbers are in the Organic Seed Alliance chart on page 25 of this pdf, a great guide to seed saving written by an organic seed farmers’ nonprofit.) So it’s not the same for every variety, and more isolation is better to be safe than sorry I suspect:


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