How to Save Tomato Seeds to Grow Next Year

Anyone who has composted leftover tomatoes has probably had the experience of seeds from those tomatoes "volunteering" in the garden if the compost that has overwintered is then used as a soil amendment or mulch the following spring. Or perhaps you've seen tiny tomato volunteers spring up in the garden where tomatoes have fallen off the plant the previous year. Tomato fruits are laden with tiny seeds that will readily sprout if they reach the soil. But rather than waiting for accidental volunteers, it's quite easy to save seeds from tomato fruits so you can plant them exactly when and where you want.

When to Save Tomato Seeds

Tomato seeds can be collected from fruits that are fully ripe, from mid-summer to fall. Tomatoes are a rather slow-growing plant, so most gardeners will want to start these seeds indoors quite early in the spring. It can take tomato seeds six to eight weeks to become viable seedlings, then once planted outdoors, the seedlings may require as much as two months to produce ripe fruit. This varies somewhat depending on the variety and size of the tomatoes—small cherry or pear tomatoes will begin bearing fruit much faster than large beefsteak tomatoes, for example. But overall, tomatoes are one of the slower-growing vegetable plants

Working With Tomato Seeds

Seeds from many plants can be saved simply by waiting for seed pods or fruit to dry, then opening them up to collect the seeds. Tomatoes take a bit more work because their seeds are enclosed in a gel-like sack that contains growth inhibitors to prevent the seeds from sprouting inside the tomato. The best way to remove this gel covering is to allow the fruits to rot and ferment. In nature, this happens when the fruit falls off the plant. For seed savers, we're going to speed up the process.

The first step is to choose your best-looking tomatoes. You want to save seed from the finest fruit, so that next year's plant will have good genes. Remember you should only save seeds from open-pollinated (OP) tomatoes. That includes all the heirlooms. Seeds from hybrid tomatoes, while they may sprout and grow, often produce tomato plants that revert to one of the genetic parent plants, which can produce much different fruit than you're expecting.

Project Metrics

  • Working Time: 1 hour
  • Total Time: 3 days
  • Project Cost: $0 to $5

What You'll Need

Equipment/ Tools

  • Mixing bowl
  • Canning jar
  • Colander

Materials

  • Ripe tomatoes
  • Cheesecloth or paper towel
  • Paper plate
  • Sealable envelope

Instructions

  1. Harvest the Seeds

    To start the process, slice the fruit in half so that the stem end is on one side and the blossom end on the other. This will expose the seed cavities better than if you sliced through the stem end.

    In some pasta and smaller 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. Many slicing tomatoes will require scooping out all of the flesh with the seeds. Whichever the case, scoop the seeds into a clean bowl or jar.

    Datterino tomatoes
    ABERRATION FILMS LTD/SCIENCE PHOTO LIBRARY / Getty Images
  2. Start Fermentation

    If there is not enough liquid from the tomato pulp for the seeds to float in, add up to a cup of water to help separate the seeds from the pulp. Then set the bowl or jar of tomato seeds and pulp in a warm, out-of-the-way spot. You will need to allow 2–4 days for the fermentation to take place. As it does so, the mixture is going to begin to smell awful, so store the bowl where you won't pass by it frequently.

    If you have glass canning jars available, they make a good container for fermenting tomato seeds. The extra space at the top of the jar controls some of the odor and the clear sides let you keep tabs on what is happening. Covering the top of the jar with cheesecloth or paper towel will keep fruit flies out and also diminish the spread of the unpleasant odor.

    Remember to label each variety.

    Processing Tomato Seeds

    © Marie Iannotti

     

  3. Check on the Fermentation

    Every day or so, check on the process of the fermentation. What you eventually want to see is a layer of mold on top of the seeds and pulp. The process is done when bubbles start rising from the mixture 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.

    Fermented Tomato Seeds
    © Marie Iannotti

    It is harder to see the layer of mold through the glass jar, but you can generally tell the fermentation is complete when the seeds settle to the bottom of the jar in a watery liquid and the thicker pulp and mold sit on top of them.

    Checking Tomato Seeds in Jar
    © Marie Iannotti
  4. Separate the Seeds

    Finally, you can remove and dispose of the mold covering. Lifting it before rinsing the seeds will make rinsing easier, but it's not necessary. You can add some water to the jar or bowl and stir or shake vigorously. The good seeds will settle to the bottom, allowing you to drain off the excess first.

    Saving Tomato Seeds - Cleaning the Seed
    Saving Tomato Seeds - Cleaning the Seed Marie Iannotti
  5. Clean the Seeds

    Strain the seed mixture into a colander and rinse the seeds well under running water. Try to remove any remaining pulp bits and mold, so that only clean seeds remain.

    Washing tomato seed (Solanum lycopersicum, syn. Lycopersicon esculentum) before sowing
    Simon Wheeler Ltd / Getty Images
  6. Dry the Seeds

    Spread the seeds onto either a paper plate or glass dish to dry. Don't use paper or paper towels or the seeds will stick to them and be difficult to remove. Set them in a warm, dry spot and allow the seeds to dry completely. Shake them on the plate daily to make sure they don't clump and that they dry evenly. Don't try to speed the process by using heat or you might destroy the seed.

    Drying Tomato Seeds

    © Marie Iannotti

     

  7. Store the Seeds

    Once the seeds are thoroughly dry, you can store them in an airtight container, in a cool, dry place. The envelope shown here will be placed in a canning jar. Remember to label and date your seeds.

    Gardening Tip

    While many tomatoes lend themselves to seed saving, it is especially beneficial to focus on heirloom tomato varieties for this activity. A great many of these vintage types of tomatoes are at risk of being lost. And in addition to being rare, heirloom tomatoes often are especially flavorful and my have unusual colors and shapes.

    Seed Saving - Storing Tomato Seeds
    Seed Saving - Storing Tomato Seeds Marie Iannotti