How to save tomato seeds

Wondering how to save tomato seeds? While these delicious veggies seem a bit tricky for seed saving, they are actually pretty foolproof.

Tomato seeds are saved from the tastiest tomatoes from at least six healthy plants. The seeds are then fermented in a jar for a few days until the gelatinous coating has dissolved, and the seeds don’t feel slippery. Wash the seeds in a fine-mesh sieve under clean water and place them out to dry for a day or two before packaging them for storage.

Read on to learn all about how to save tomato seeds!

How to save tomato seeds
‘brandywine’ tomato seeds

The basics for saving tomato seeds

Tomato seeds are one of the most commonly collected types of seeds. Some of the best-tasting tomatoes are open-pollinated varieties that are perfect for annual seed-saving as they grow “true to type”. This includes favorites like Brandywine, The Black Krim, Black Cherry, Mortgage Lifter and Green Zebra.

Tomatoes have self-pollinated flowers. The flowers can be pollinated by the wind or when the plant is jostled. A common practice is to gently tap the flower clusters with your fingers as the flowers bloom to encourage pollination and fruit set.

Many modern tomato varieties don’t easily cross-pollinate with other varieties because the stigma of the flower is inserted and not accessible by pollinators. That said, currant tomatoes and potato-leaved varieties may be more prone to cross-pollination than other varieties.

Tomato seeds are harvested and prepared for storage using wet process fermentation. Fermenting tomato seeds removes the gelatinous coating around each tomato seed (or other similar types of seeds like saving seeds from cucumbers).

The gelatinous sack around the seed keeps the seed from germinating too early inside the fruit in nature, but it can inhibit germination altogether sometimes. For this reason, seed savers dissolve the coating off of the seed with the wet fermentation process prior to drying and storing the seeds.

Planting tomatoes for seed saving

To start, you’ll need to grow some delicious tomatoes! Begin by planting at least six plants of your desired type of open-pollinated tomatoes. If possible, 12 or more plants are best for preserving genetic diversity. This will help ensure that you have a good variety of seeds to work with.

“Tomatoes are inbreeding plants. Most modern tomato varieties have totally retracted styles. Such flower structure severely limits (and may totally preclude) any crossing between these varieties.”

Seed to Seed: Seed Saving and Growing Techniques for Vegetable Gardeners, by Suzanne Ashworth

Choose an open-pollinated variety

Check that you have chosen an open-pollinated variety of tomato for saving seeds . These can be heirloom tomatoes or non-heirloom (newer) varieties, as long as they are not hybrids (F1 crosses). Seeds saved from hybrid tomatoes like Sungold, Burpee’s Big Boy, and Celebrity won’t breed true to the parent plant.

Here are some great open-pollinated tomato varieties:

Heirloom seeds have been saved for generations and are well-worth preserving for future generations!

Isolation between varieties

The group of 6-12+ tomatoes needs to be isolated from other types of tomato plants. The variety you’re saving can be isolated from others simply by planting them far away from other varieties (or only planting one variety) or by putting a physical barrier between varieties.

Isolation by distance is the easiest method for small-scale home seed saving. The minimum isolation distance for most tomato varieties is about 10 feet (3 meters). That said, some heirloom varieties have long styles inside the flowers (longer than the stamens) and may be more prone to natural cross-pollination. An isolation distance of 30 feet (10 meters) is recommended for these more-susceptible cultivars. For commercial seed production, it is not uncommon for producers to isolate varieties by 100 feet (30 meters) or more.

Isolation with a physical barrier is usually done with row cover. The tomato plants can be grown in polytunnels, greenhouses, or hoops covered with insect netting. Be sure to affix the insect netting tightly to the ground and around the edges to prevent bumblebees, mason bees, flies, and other pollinators from entering.

Companion planting for seed saving

Also, take time to plant lots of flowers around the garden area. These flowers are to distract pollinating insects and keep them busy.

We want the bumblebees going to nearby flowers instead of potentially crossing nectar between tomato varieties. Cross-pollination of one variety with another can certainly still occur, but beneficial pollinators usually prefer native flowers instead of tomato blossoms.

Consider planting a tall hedge-like crop like corn between varieties, or a flowering crop like squash. Try to plant crops and companion plants for tomatoes that flower at different times in the summer to distract the pollinating insects. Alternatively, you can use an organza blossom bag around a flower cluster to minimize cross-pollination.

Growing open pollinated tomatoes for seed saving

Growing tomatoes for seed saving

Keep your newly-planted tomato plants healthy by providing consistent water, removing any diseased leaves, and providing a tomato stake and/or tomato cage. You’ll also want to add some slow-release organic fertilizer and mulch the surface of the soil to retain moisture and keep the roots cool.

As the tomato plants start to flower, take a bit of time every day to tap the flower clusters or gently jostle the whole plant. Each tomato flower is self-fertile and has both male and female parts. Jostling the plant can help pollinate the plant by causing the pollen to fall from anthers onto the stigmas of the blossom. Wind can also make this happen all on its own.

Choosing tomatoes to save seeds from

Watch for the first clusters of tomatoes to ripen on each plant. You’ll want to pick a few of these first-ripening tomatoes from each plant. If you have more than 6-12+ plants, consider only harvesting from the plants in the middle of the patch to lessen the chance of cross-pollinated seeds.

Look for vigorous plants that flowered early in the growing season for saving your own tomato seeds. Avoid harvesting tomatoes from sick, diseased, or weak plants in the vegetable garden. Try to choose healthy uniform plants that have lots of flowers/fruit for saving your own seeds.

Harvesting tomatoes for seed saving

The tomatoes should be ripe when harvested. Most varieties are a red shade when ripe, but there are many that are different shades (purple, yellow, et cetera) when perfectly ripe. They should still be a bit firm but should have a bit of give when squeezed.

Try to pick the ripe fruit from within the center of the tomato plant (rather than hanging out the side of the cage, where the flowers were likely more susceptible to cross-pollination). If frost is on the way, the tomatoes can be ripened off the vine indoors on a windowsill. Don’t save seeds from rotten tomatoes.

Determinate tomatoes are varieties that grow to their genetically-determined height and then set all their fruit at once. These varieties are great for saving lots of seeds at once. Indeterminate tomatoes grow intermittently on vines that get longer and longer throughout the growing season. These varieties are perfect for saving seeds in smaller batches over a longer period of time.

How to save tomato seeds?

The process for saving tomato seeds is pretty simple. Fortunately for seed savers, tomato seeds are ready to harvest at the same time that tomatoes are perfectly ripe to eat! You can use the seeds and pulp for seed saving and still get some tomato slices for sandwiches or tomato paste.

Start by slicing into the fruit through the thickest part (imagine the equator). Taste the tomato itself. Choose the tastiest tomatoes from each plant to save seed. Don’t harvest tomato seeds from moldy or rotten tomatoes.

“For many gardeners, tomatoes are the archetype of diversity. The myriad shapes, colors, and sizes of open-pollinated tomato cultivars can inspire a gardener to save seeds from numerous varieties of tomatoes.”

The Seed Garden: The Art and Practice of Seed Saving, by Micaela Colley and Jared Zystro

Harvesting tomato seed

Now its time to collect the seeds from inside the tasty tomatoes and get them started on the fermentation process. To get viable seeds, you can simply save the seeds from a single plant, but for genetic preservation, save them from a minimum of about 20 different plants of the same variety.

For fermenting tomato seeds, you’ll need:

  • Knife
  • Glass jar
  • Spoon
  • Elastic band
  • Cloth, paper towel, coffee filter, or window screen
  • Fine-mesh kitchen sieve
  • Plate

Squeeze or scoop the seeds and their pulpy coatings into a glass canning jar (or cup or bowl). Smaller tomatoes can simply be mashed up whole if desired.

Add some water to the bowl and mix the tomato pulp and seeds around gently with your fingers. If there’s not much tomato pulp in the jar, add a pinch of sugar to help with fermentation.

Mix gently again and (optionally) cover using an elastic with a cloth, paper towel, paper plate, or coffee filter.

Fermentation method

Set the jar of wet seeds on the counter. Fermentation will occur naturally in the seed mixture and start to dissolve the gelatinous layer from around the seeds.

Stir the seeds a few times a day to prevent a thick layer of mold from growing on top of the seeds. Each time you stir, pull out a few seeds and see if they still feel slippery (meaning there is some gel remaining).

Try not to cover the container with a tight lid. If flies are a problem, use a breathable cover like cheesecloth to cover the top of the jar/tub.

Dissolving the layer completely usually takes 1-3 days. The rough edges of the seeds can be felt when the gel layer has dissolved.

“In addition to removing the gel sack, fermentation also kills many seed-borne tomato diseases.”

Seed to Seed: Seed Saving and Growing Techniques for Vegetable Gardeners, by Suzanne Ashworth

Cleaning the seeds

Once the tomato gel coating has dissolved, the seeds must be separated out from the pulp in the jar. Add some more fresh water to the jar and swirl it around. The viable seeds will sink to the bottom of the bowl while the pulp and other matter will float to the top.

Pour off as much water as possible while keeping the seeds in the jar. Repeat this process until the water runs clear. Then pour the seeds into a fine-mesh strainer or kitchen sieve and spray fresh clean water over them.

Drying tomato seeds

Now the seeds need to be gently dried, promptly. You can let the excess water drain out from the seeds while they are in the sieve, and then place the seeds in small groups to dry on a plate, paper towel, window screen, or coffee filter. You can also use a specialty seed-cleaning sieve if you have one.

Place the seeds in a warm spot with excellent air circulation to dry. A minimum air temperature of 70°F (21°C) will help them dry quickly, but you’ll want to avoid baking the seeds in truly hot conditions. Drying seeds usually take only a day or two. Let the seeds dry completely before packaging them for storage.

Storing tomato seeds

Once your seeds are completely dry, store them in a cool, dry, dark place in a labeled envelope, baggie, or airtight container like a glass jar for seed storage. Keep vegetable seeds away from moisture, warm temperatures, and direct sunlight

Dry seeds saved in paper envelopes lose their viability quickly, so if you’d like to store them for over a year, use a glass jar. Be sure to label the container with the name of the tomato variety and the date saved. You can do a germination test at any time to determine the germination rate of your seeds.

Tomato seeds have a long seed life and can last for over five years when properly stored. But if you have any doubts about their viability, it’s always best to test their germination (or start with fresh seeds).

Packaging tomato seeds

Start by packaging the clean, dry seeds in a small package. Here are some good options for storage containers:

  • Small paper coin envelopes
  • Small plastic baggies
  • Glass wide-mouth mason jars

Press very lightly when closing the package to avoid crushing the seeds if using an envelope or bag. Try not to leave too much air in the package, but don’t press out all of the air either (and don’t vacuum seal seeds).

Label the seeds before putting them into storage. Include the variety name, the date the seeds were saved, and cultivation tips.

Seed storage containers

Once the seeds are packaged for storage, all the packages can be placed into a container. This can be anything from a repurposed plastic bin or wooden box to one of these fancier options:

  • Library card drawers
  • Photo storage cases
  • Glass wide-mouth mason jars

Airtight containers like large Ziplocs, plastic tubs, or mason jars work well for small seeds like this. If you can find an airtight tub that is a solid color, that will help keep light away from the seeds. Wooden library drawers – while not airtight – do an excellent job of keeping light out while maintaining organization.

Glass storage containers tend to help seeds remain viable for the longest time. Thick plastic can also do a good job for several years.

To reduce humidity, tuck a silica gel pack from other packaging or include a tablespoon of dry rice. These drying agents can absorb excess moisture.

Seed storage conditions

Tomato seeds last the longest when stored in ideal conditions. This generally means a location with low humidity (but not zero humidity), no light, and a cool temperature just above freezing.

Here are the ideal conditions for storing tomato seeds at home:

  • An air temperature of 32°-41°F (0°- 5°C)
  • An air humidity of less than 50%
  • Near-total darkness
  • Free from pests like mice that like to feast on seeds

Common places to store seeds include unheated closets, dry and cool basements, and the crisper drawer of the refrigerator. If storing in a place with variable humidity (like the fridge), be sure to use an airtight container and consider popping a humidity meter in with your seeds.

Tomato seed lifespan

Tomato seeds usually last for 4-6 years when properly stored at home in a cool, dry place. That said, they may only last a couple of years if stored in paper rather than glass. They can last much longer than 6 years in commercial storage conditions with low levels of oxygen.

Planting tomato seeds

Tomato seeds are typically sown indoors, grown into seedlings, and then the baby plants are transplanted out into the garden. Tomatoes can be direct-sown outdoors, but only in climates with very long growing seasons.

Tomato seeds germinate in soil temperatures between 50ºF and 95ºF. Germination is quite slow at the cooler end of this range, so tomato seeds are usually planted at an optimum soil temperature of 65ºF to 85ºF. A warm room in your home with a seedling heat mat is a wonderful option.

Viable tomato seeds usually take about a week to germinate unless the soil is overly cold. Don’t plant your tomatoes outdoors until air temperatures are a minimum of 42°F (6°C), and preferably above 50°F (10°C). Add a tomato stake and/or a cage when transplanting your seedlings.

Mary Jane Duford
Mary Jane Duford

Mary Jane Duford is a quintessential Canadian gardener. An engineer by trade, she tends to an ever-expanding collection of plants. In her world, laughter blooms as freely as her flowers, and every plant is raised with a dash of Canadian grit.

Mary Jane is a certified Master Gardener and also holds a Permaculture Design Certificate. She's also a proud mom of three, teaching her little sprouts the crucial difference between a garden friend and foe.

When she's not playing in the dirt, Mary Jane revels in her love for Taylor Swift, Gilmore Girls, ice hockey, and the surprisingly soothing sounds of bluegrass covers of classic hip-hop songs. She invites you to join her garden party, a place where you can share in the joy of growing and where every day is a new opportunity to find the perfect spot for yet another plant.

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