Save seeds from your garden watermelon this year and save yourself the expense of buying seeds next spring. You can save the seeds from the watermelon without sacrificing the fruit. Watermelons easily cross-pollinate, so only plant one variety in the garden if you want to save the seeds. Hybrid watermelons do not produce viable seed, so it is not possible to save seed from supermarket melons, as most of these are hybrids. When choosing melons for the home garden, pick varieties labeled as heirloom or non-hybrid so they produce viable seed.
Cut a ripe watermelon in half. Remove the flesh and pick out the seeds. Set the flesh aside to eat later, and place the seeds in a colander.
Squeeze a drop or two of unscented dish soap onto the seeds. Swish the seeds around with your hands so the dish soap coats them, then rinse the soap off with cool running water. The dish soap removes the sugars from the seed coat, which prevents rot during storage.
Spread the seeds out on a sheet of paper towel and set them in a well-ventilated area that is out of direct sunlight. Dry the seeds for seven days, turning them over halfway through the drying period. Replace the paper towels if they become damp.
Label an envelope with the watermelon variety and year harvested. Place the seeds inside the envelope and seal closed.
Store the watermelon seeds in a cool, dark and dry place until you are ready to plant in spring. Or, place the envelope in a sealed glass jar and store in the refrigerator.