After fermenting and washing tomato seeds, Sam Schipani lays them out on labeled coffee filters to dry before storing them. Credit: Linda Coan O'Kresik | BDN

This story was originally published in August 2018.

Tomatoes are a summer favorite. When you get a really amazing tomato, you should consider saving its seeds for future planting seasons.

Saving seeds at the end of a season’s harvest will help you save money, have stronger tomatoes and also save the stock of seeds for the future.

“Our food system would be less stable if we were just relying on one or two varieties because they won’t have the resilience when disease and other pressures come along,” said Kate Garland, horticultural specialist at the University of Maine Cooperative Extension. “It’s really important in our food system to have a lot of varieties. Saving seeds is an important way of contributing to that.”

Plus, Garland said, seed saving is “really fun.”

Seeds from many plants can be saved simply by collecting them from the fruit or vegetable, rinsing them, drying them and storing them.

For tomato seeds, which are enclosed in a gel-like sac that contains growth inhibitors that prevent the seeds from sprouting inside the tomato, the process is a bit more complex.

BDN Homestead writer Sam Schipani squeezes a tomato to remove its seeds and juice on Aug. 7. Credit: Natalie Williams | BDN

“You can scoop them out, clean them the best that you can with a kitchen strainer and dry them, [but] the gelatinous layer will dry and delay germination,” said Caleb Goossen, organic crop and conservation specialist at Maine Organic Farmers and Gardeners Association.

Goossen said that removing the gel is not critical to the success of saving seeds, but the longer seeds take to germinate in the spring, the greater chance the seedlings have of succumbing to soilborne pathogens or disease.

The best way to remove this gel covering is to allow the fruits to rot and ferment over the period of a few days before storing the seeds. If you’re ready for a little bit of stink and some patience, here is the best way to save tomato seeds for a great harvest next year.

Choosing tomatoes to save seeds

To start, choose your tomatoes. Garland said that this can be more difficult than the fermenting process itself.

First, determine whether your tomatoes are a hybrid variety. This information is usually on the seed packet, which will read “hybrid” or “F1 variety.”

BDN Homestead writer Sam Schipani prepares to harvest seeds from tomatoes in her home kitchen on Aug. 7. Credit: Natalie Williams | BDN

“Hybrid tomato seeds are produced by cross pollinating a very inbred mother line, very inbred father line to create offspring, which is called the F1 generation,” Goossen said. “That gives the crop what is called heterosis [or] hybrid vigor [which results in] very uniform crops with very specific characteristics, but if you save seeds from those varieties, it will re-sort the genetics of the plant and you’ll have a mishmash of traits.”

It is possible to save seeds from hybrid tomatoes, to be sure, but the results can be unpredictable.

“You’ll get a wild card out there,” Garland said. “I would be really disappointed [if] I grew a tomato variety that never fruited.”

For saving seeds, an open pollinated variety or an heirloom variety is best.

However, if you have multiple types of tomatoes in the same garden, bees and other pollinators may take pollen from one variety to another, resulting in seeds with an unpredictable mix of genetic material. Consider isolating the tomatoes you want to save from other tomato varieties by at least 10 feet.

“It does take some forethought,” Garland said. “It may be a little bit late to do it this year. Pollinators can play a role in playing cupid and giving the genes from one variety and moving that to another variety.”

If you haven’t isolated your tomatoes, Goossen said not to worry too much about making absolutely pure lines, especially if you are saving seeds for fun.

Choose tomatoes from your best tomato plants. You can judge your tomato plants based on the taste of the fruit, or on their yields. Regardless, though, they should be disease-free, healthy and free of insect pressures.

Once you have chosen the plant, pick your fruit. Fully ripe, disease-free tomatoes are the best candidates for seed saving. Goossen said to look out for cracking, browning and deformities at the blossom end to weed out fruits that are unfit for the seed saving process.

Fermenting tomato seeds

To start the process of saving tomato seeds, slice the fruit in half to maximally expose the seed cavities. In some tomatoes, the seeds are so concentrated in the cavity that you can scoop them out and still be able to use the flesh of the tomato for cooking.

“You only need gelatinous parts of fruit, not the meatier sections,” Goossen said. “Some varieties produce fewer seeds per fruit than others, some will have many, many seeds.”

Scoop or squeeze the seeds (the method will depend on both your personal preference as well as how meaty the tomato is) into a jar or container that you don’t mind getting dirty or disposing of at the end of the process. Old canning jars are good because they will allow you to see the fermentation process.

Label the variety on each jar. If there is not enough liquid from the tomato pulp for the seeds to float in, add water to help separate the seeds from the pulp. Cover the top of the jar with cheesecloth or a paper towel to keep fruit flies out and also diminish the spread of the unpleasant odor.

Set the container in a warm, out-of-the-way spot and leave it for about three days — a shady garage or shed, Goossen said, is a good choice. Stir the fermenting juices to submerge the pulpy material once or twice daily to prevent the build-up of mold, which is not harmful to the seeds but may discolor them.

Eventually, there will be a layer of mold on top of your seeds and pulp. The fermentation is complete when bubbles start rising from the mixture, the seeds settle to the bottom of the jar or when the entire layer of tomato pulp is covered with mold. Don’t leave the seeds fermenting past this stage or they may begin to germinate.

Tomato seeds fermenting in jars. Credit: Linda Coan O'Kresik | BDN

Remove and dispose of the mold covering. Add some water to the jar or bowl and stir or shake vigorously. You can also clean the seeds by straining the seed mixture and rinsing under running water.

Once only the seeds remain, allow them to dry on paper plates or a coffee filter (Garland said not to use paper towels, which can stick to the seeds). Shake gently to make sure they don’t clump and that they dry evenly.

“Write the variety on the paper plate,” Goossen said. “You want to keep them well labeled so you know what you’re growing next year.”

Leave the seeds to air dry for a week or two in a warm, out-of-the-way spot, like on top of the refrigerator.

When the seeds dry, they will appear slightly fuzzy, but not moldy. A properly dried seed will snap when bent in half; test one before storing the rest.

Storing tomato seeds

Once the seeds are fully dry, store them in an airtight container.

“I like to reuse little glass jars, baby food jars, old spice jars [or] sometimes I make envelopes,” Goossen said.

Keep these envelopes in a cool, dry place.

“You want to think about it as providing just the opposite conditions that you would provide when you’re germinating them,” Garland said. “When you’re germinating them, you want warm moist conditions. When you’re storing, you want cool dry conditions.”

Garland said that she stores seeds in an envelope or a waterproof container like a mason jar in the back of her refrigerator. Goossen said he keeps his in the freezer.

Once they are stored in a cool, dark place, your tomato seeds can stay viable for up to six years. Save your tomato seeds for the years to come, or share them with friends so they can start their own tomato seed saving adventure.