Preserving tomato seeds from your current year's crop is a great way to get next year's garden started with little monetary investment. Each tomato comes filled with many seeds, so saving just a few tomatoes can yield a high number of seeds for you. Tomato seeds preserve fairly easily. In the right conditions, they can stay viable for 50 to 100 years after harvesting. Seeds can be preserved with just a few materials and a little bit of time.
Select very ripe tomatoes and cut them in half. Squeeze them until the pulp and seeds fall into a small plastic container.
Leave the pulp and seeds outside in a warm location for three to five days. They should mold over, which will help preserve the seeds. The seeds will sink to the bottom.
Add water and stir. Strain the seeds to remove the pulp. Repeat the process until the seeds are thoroughly rinsed off.
Spread the seeds out on cheesecloth or a coffee filter. Lay them out on a cookie sheet or similar pan that is lined with paper. Leave them until dry. This may take 10 to 15 days.
Put the seeds into an airtight container. Store them in a cool, dry place until ready to plant.