The Tomato BookZone 6
A sliced tomato with seed gel on a wooden board beside a jar
A sliced tomato with seed gel on a wooden board beside a jar

Chapter 10 · Ferment, rinse, dry

Harvesting Seeds

Tomato seed is wet seed. The gel around it is a germination inhibitor. Fermentation is how you take that gel off and keep a cleaner, longer-lived seed.

Zone 6: transplant Mid- to late April. Harvest June – October.

Saving tomato seed is the most satisfying hour of the year if you grow open-pollinated plants. You are not just putting next spring in a jar. You are keeping a line that already liked your soil, your water, your pests.

You can rinse and dry without fermenting. Those seeds will often sprout next spring. They keep a year or two, they look shabby, and they carry more of the fruit’s pathogens. Ferment two to three days. It is the method seed savers use because it works.

  1. 01

    Choose the right fruit

    Save seed only from open-pollinated or heirloom plants — not F1 hybrids, which will not come true. Pick the best fruit on the healthiest plant: fully ripe, even overripe, never green. One excellent tomato is better than a bowl of average ones.

  2. 02

    Scoop the gel

    Cut the tomato across the equator, not stem to blossom. Squeeze or scoop the seed gel into a clean jar. Keep varieties in separate jars. Add a splash of water — about a quarter cup — so the mash can ferment.

  3. 03

    Ferment two to three days

    Cover loosely. Set the jar at room temperature, 70–80°F, out of sun. Stir once a day. A thin film of mold is normal; it is the gel coat breaking down, and it reduces some seed-borne diseases. Stop at two to three days. Longer fermentation cuts germination.

  4. 04

    Rinse until the water runs clear

    Add water, let viable seeds sink, and pour off mold, pulp, and floaters. Repeat. Rub remaining pulp in a strainer under a slow tap. Good seed feels gritty, not slimy.

  5. 05

    Dry thoroughly

    Spread seeds in a single layer on a ceramic plate, coffee filter, or screen — not paper towel, which glues itself to wet seed. Dry 7–14 days in moving air, away from sun and ovens. Stir daily. They are done when they snap, not bend.

  6. 06

    Label at once

    Variety, year, and where the plant grew. You will not remember in March. Use a pencil on kraft envelopes; ink can bleed if a jar sweats.

Tomatoes are mostly self-pollinating. For home use, a few feet between varieties is enough. If you are keeping a rare line pure, bag a few blossoms before they open, then save seed only from those fruit.