Have you ever wondered how to save tomato seeds? We all put so much time in growing our beloved plants that it seems a shame to only enjoy that harvest for one growing season. Whether you’re thinking of saving heirloom tomato seeds or not, this guide should help you with all aspects of tomato seed saving.
But seed saving has to start somewhere. And the first step of that is harvesting tomato seeds. We’ll also go over methods of saving tomato seeds without fermenting as well as fermenting tomato seeds, how to dry them properly, and more.
So if you’d like to start saving tomato seeds every year, this guide should walk you through everything you could ever need to know!
We also have a great video where Kevin goes over the fermentation process with Brijette Romsedt of San Diego Seed Company. You can see that here, too!
Choose Your Tomatoes Wisely
What kind of tomatoes are you growing, and are they open-pollinated varieties?
When you’re growing tomatoes, the resulting seed of tomato varieties will be developed based on what pollinated the parent plant’s flower. Let’s say all you’re growing is the San Marzano variety of paste tomatoes. Even if bees end up cross-pollinating your plants, they will likely breed true as San Marzano tomatoes. That’s a single-variety open pollination.
But open-pollinated varieties can be cross-pollinated from different species. Let’s say you have that San Marzano, but you’re also growing a Cherokee Purple, a 4th of July, and a Yellow Pear tomato. That’s now one paste tomato, one heirloom slicer, one salad slicer, and one cherry tomato variety. Those can also be cross-pollinated by your bees.
The resulting fruit from those cross-pollinations may not be 100% identical to its parent plant. The fruit itself will taste like what you planted, but the seeds may now be carrying traits from other species. This is how hybridization happens over multiple generations of a plant.
For the most true tomato development, you’ll want to stick with just one variety of tomatoes in a given location. You’ll then be reinforcing that cultivar’s genetics, plus over time they’ll adapt better to your specific climate. If you don’t mind potential gradual changes over time, cross-pollinated seeds can still grow, too. But you may want to buy new seed every few years to revert to a truer form.
Pick only the best, biggest, juiciest, and most impressive tomatoes to harvest your seeds from, and mark those in advance. I use a piece of yarn tied around the branch next to the tomato as a marker. You want them to ripen on the vine, and in fact, you want to leave those on the vine until they go over-ripe and a little squishy.
Pre-selecting and waiting for these prime candidates means you’re going to get seeds from that specific perfect fruit. That reinforces your chances for getting more fruit just like those!
Fermenting Tomato Seeds
Did you know that tomatoes have germination inhibitors around their seed? That gelatinous coating that surrounds the tomato seeds prevents them from sprouting. On the one hand, that means that your tomatoes aren’t sprouting new fruit on the vine. But it also means that for the best seeds, you’ll need to remove that gel.
The easiest way to do that is through tomato seed fermentation. As the gel breaks down, the seeds inside are released and are then free to germinate. Each variety of tomatoes should be fermented on its own, not mixed with seeds from other varieties.
Begin by washing off your tomatoes thoroughly to remove any dirt that might be on the outside of the fruit. It reduces the chances of any soilborne bacteria infecting your seeds. If they’ve gone really soft, be careful not to pop them open when you do this.
Now it’s time to discuss how to harvest tomato seeds. Slice the tomatoes neatly in half or in quarters lengthwise along the fruit. Then, holding the stem end of the tomato, use your hand to squeeze the seeds and fruit pulp downward into the bowl. Sacrifice a few of these over-ripe tomatoes to squeeze into juice, too. This juice will speed up the fermentation process. Any leftover, seedless tomato flesh that isn’t spoiled can be dehydrated and used like a sundried tomato.
Put your tomato juice, seeds, and gel into a quart-sized mason jar. Ideally, there should be enough juice in there so that the gel will be separated from the seeds by some liquid once fermentation is complete. If there isn’t, don’t add water, as diluting the juice will actually slow down the fermentation process.
Once the lid is on the jar, give it a good shake and then set it in a location that’s 70 degrees Fahrenheit or less. Once or twice a day, give it a good shake to try to dislodge the seeds from the gel. Be sure to open the jar at least once a day to “burp” it, allowing any gasses from the fermentation process to escape. It may smell bad, but don’t let that worry you. Do this for at least three days and up to a week.
At the end of the fermentation process, add about three times the amount of water to the jar, give it another shake, and let it sit for an hour or so. Most of the viable seeds should fall to the bottom of the jar, and the gooey gelatinous layer should float on the surface. Use a spoon to scoop out the gel layer and dispose of it.
Pour off some of the excess pulpy water, add fresh water, shake, and repeat this final draining process again until the water looks mostly clear. Each time, give it enough time to settle, with the viable seeds falling to the bottom and the non-viable ones floating, and scoop off the waste. Once the water is clear, dump the contents into a fine mesh strainer and thoroughly wash them off.
If you’re doing a lot of seeds, you can speed up the rinse process by scooping off the initial gel, dumping the rest onto a large screen or into a large mesh strainer, and spraying it with a hard jet of water. The seeds won’t go through the screen or strainer, but any residual gunk will.
Some people at this point opt to treat the seed to prevent transmission of any diseases. This step is optional, but is recommended if you plan on sharing seeds with others.
To treat the seed, make a 10% bleach solution (1 part bleach to 9 parts water) and soak the seed for 30 minutes. Immediately dump the seeds back into the strainer and rinse them under cold running water for at least 7 minutes, constantly stirring or agitating the seeds to make sure they are completely rinsed off. Once you’ve rinsed for at least 7 minutes, move on to drying.
Why seven to eight minutes of constant stirring under running water? Because this reduces the amount of residual chlorine from the bleach to below the National Organic Program’s threshold. Residual chlorines on the seed have to be at less than four parts per million to consider the seed organic.
How To Dry Tomato Seeds
We need cool, well-ventilated conditions to dry out our tomato seeds in. If it’s too hot, like dehydrators or other similar machines, it can cook the tomato seed and cause it to become sterile. That’s the last thing we want to happen!
You can leave your tomato seeds out in a dry place. If doing so, I recommend making a wooden drying frame out of a few pieces of scrap wood and an old window screen. Use a staple gun to attach the screen to the frame. You can then spread out your seeds on that and place it in a dry place that’s well-ventilated.
If you don’t want to make a drying frame, you can lay a piece of parchment paper on a baking sheet and put your seeds on that. It will take a bit longer for them to dry in this method, but they’ll still dry out over time. Some people even use a paper plate for this, but with a paper plate, they can get stuck to the surface and might be trickier to remove. As the parchment paper is more flexible, you should be able to bend it and pop stuck-on seeds right off.
Every day or two, you’ll need to come by and stir up your seeds to make sure they’re all drying out evenly. Break apart clumps that stick together with your fingers, or rub them in your hands until they come apart.
There is another method for drying seeds without hea. Use a box fan and two inexpensive air filters, as well as a few bungee cords. Once the fermentation process is done, save tomato seeds between those filters, strapped to the fan. The fan will force cool air through the seeds and dry them out much more rapidly than if they were just lying in a still-air environment.
Saving Tomato Seeds Without Fermenting
It is possible to save tomato seeds without fermenting. Eventually, the gel coating will break down on its own, which is why it’s possible to plant a chunk of seedy tomato and get sprouts. This method is great if you’re just saving a few seeds for yourself and don’t plan on treating the seeds to prevent disease spread.
For this method, you’ll need paper towels, a pair of tweezers, and your fresh tomato of choice. Cut open the tomato and scrape out the seeds into a bowl. With your tweezers, pick up individual seeds along with their gelatinous goop and press them onto the paper towel, making sure to space them out. Lay these paper towels somewhere dark, cool, and well-ventilated to let the seeds dry out completely.
Once dry, the seeds will be stuck to the paper towel. You can fold up the towel and store it for later, and can even write the variety of seed on the towel if you want. When it comes time to plant next year, cut or rip off individual segments of towel and tomato seeds for planting. The paper towel will break down and the seeds will germinate.
Please do note that using this method means that you don’t reduce your chances of spreading disease. Since you’re including the dried gel on the non-rinsed seeds, there is a slight risk if any of your tomatoes were harboring a potential disease. But the risk is fairly minimal if you’ve been disease-free.
Three words apply to storing your tomato seeds: cold, dry, and dark.
You don’t have to freeze your seed, because tomatoes don’t need that much cold. But they do like it cool in terms of temperature. Aim for a temperature range of 40-60 when possible, but don’t panic if your house is usually 70 degrees, that’ll be fine too.
Keeping the seeds dry is essential. Moisture is necessary for germination, and your tomato seeds will happily sprout in the dark if they have access to moisture. I like to store mine in an airtight container, in paper envelopes with a moisture absorbing silica packet amongst them.
Finally, the darkness also prevents early germination. While seeds don’t need light to sprout, any that have access to warmth and moisture still might. But in the absence of moisture or warmth, the darkness is ideal for long-term storage.
We have a lot more in-depth storage tips for a variety of seed types in our seed-storing article.
So that’s how to save tomato seeds in multiple different ways. You can now start collecting tomato seeds from your preferred plants and keep the harvest going year after year!