How to Save Tomato Seeds

The Short Version

You mash up a tomato to get all the seeds and juice out, let that mixture ferment for several days, rinse the seeds clean, and dry them. The fermentation step is the part most people skip or don't know about — it breaks down the gel coating that prevents seeds from germinating inside the fruit, and it kills most seed-borne diseases in the process.

This works for any open-pollinated (heirloom) tomato. Hybrid seeds won't come true to the parent, so save seeds from heirlooms specifically.

What You Need

• A glass bowl or small plastic cup
• A mesh strainer with holes small enough to catch seeds
• A coffee filter and a plate or small bowl for drying
• A small envelope, zip-lock bag, or airtight container for storage
• A paper towel and rubber band
• Silica desiccant packs (optional but helpful for long-term storage)

Preparation

Cut the tomato into quarters over your container so you don't lose juice — that liquid is important for fermentation. Mash everything until you have a soupy mix of seeds, juice, and pulp. You're basically juicing the tomato. If there isn't enough liquid to cover the seeds, add a small amount of tap water.

Cover the container with a paper towel secured by a rubber band. This lets air in while keeping debris and insects out.

Fermentation

Place the container in a dark, warm spot — 75 to 90 degrees is ideal. A garage works well in summer. Leave it for four to five days.

You'll see mold forming on the surface. That's normal and actually a sign the process is working. It will smell bad. That's also normal.

Cleaning

Pour the fermented mixture through your mesh strainer and rinse thoroughly under strong running water. The seeds can handle a hard spray — don't worry about being gentle here. You're trying to remove all the pulp and gel.

If bits of pulp remain after straining, put the seeds in a bowl of water and stir. Viable seeds sink and debris floats, so you can pour off the floating material. One or two rounds of this usually gets them clean enough. Small remaining bits of pulp will separate on their own during drying.

Transfer the clean seeds to a coffee filter set in a plate or small bowl. Don't use paper towels — seeds stick to them badly and you'll tear the towel apart trying to get them off.

Drying and Storage

Let the seeds dry undisturbed for one to two weeks. During the first few days, check on them once or twice and break apart any clumps with your fingers — they tend to stick together while still damp. Eventually they'll feel loose and dry to the touch.

Once fully dry, put them in a small envelope. Label it clearly — variety name, year, and any notes about the parent plant. Unlabeled seed envelopes are a reliable source of confusion by the time spring arrives.

For basic storage, a drawer or shelf out of direct light and heat is fine and seeds will stay viable for at least a year. For longer storage, put the envelope in a small airtight container with a silica desiccant pack. In the fridge or freezer, seeds stored this way can remain viable for five to ten years — though for most home growers, you'll use them long before that.