If you can grow a tomato, the hard part is done—saving the seeds is easy!

Harvest fully mature tomatoes, and even better, let them ripen a little longer indoors until they are just slightly overripe, while still edible. Tomatoes are mostly self-pollinating, but not always, so there is always some potential for varieties to cross with one another. To help prevent unwanted crosses, space different varieties as far apart as possible. Or, let nature make a cross for you—you may end up with a great new tomato!

You can save seed from as few as one plant, but saving from more plants is always better for maintaining genetic diversity and keeping your variety healthy over time.

Squeeze the seeds and their surrounding pulp into a jar and let them sit for 24–48 hours, depending on how quickly the fermentation progresses. Stir the mixture once a day and look for a layer of mold to form on the surface—this is normal and part of the process! Once the jelly-like coating around the seeds has broken down, rinse and strain the seeds several times with fresh water. The good, mature seeds will generally sink, while lighter, immature seeds and debris tend to float. Pour off the floating material and continue rinsing until the water runs mostly clear.

Spread the clean seeds out to dry completely on a cloth napkin or coffee filter. Avoid paper towels or newspaper, as the seeds can stick to them. Let the seeds dry for several days, then store them somewhere cool, dark, and dry. Properly stored tomato seeds can remain viable for many years.

Learn all you need to know about saving tomato seeds in our free guide: Saving Tomato Seeds