How to Collect Tomato Seeds Collecting tomato seeds is an easy, low-cost way to acquire desirable seeds for the next growing season. Any tomato seeds that you harvest from your garden are already adapted to your climate, your growing medium and the garden pests in your area. While collecting tomato seeds is a very easy task, you must harvest, prepare and store the seeds properly to increase their chances of germinating when you plant them next season. Instructions 1.Pick a fully mature, ripe tomato from a suitable plant. Only collect seeds from your most vigorous tomato plants that bear the best tomatoes. Harvest seeds only from heirloom or standard tomato varieties because they are far more likely to produce viable seeds than hybrid tomato species. 2.Soak your tomato seeds. Squeeze the seeds and pulp into a small bowl. Add just enough water to cover the seeds and let them sit at room temperature for about three days. Check your seeds twice a day and carefully scrape off any pulp that floats to the top of the water. 3.Let your tomato seeds dry. Gently pour the clean tomato seeds out onto a paper towel and leave them to dry at room temperature. 4.Store your tomato seeds for the winter. Put your seeds in an airtight glass container. Label the container with the collection date and the tomato variety. Keep the seeds in your refrigerator or another cool, dry and dark location. The University of Minnesota Extension notes that collected tomato seeds retain their viability for up to three years.