Watermelon seeds from this year's garden can be planted next year. Seeds saved from the fruits of your garden's non-hybrid watermelon plants (Citrullus lanatus) can grow into new plants the following season. Different varieties of watermelons can cross-pollinate, which results in seedlings that aren't exactly like their parent plants. So grow only one watermelon variety in the garden if you want to save the seeds. The large seeds separate from the fruits easily, but they require some preparation to store well. Properly saved watermelon seeds can remain viable up to four years. Cut open a ripe watermelon. Scoop the seeds from the melon's flesh, and place them in a strainer. Rinse the seeds with warm tap water, removing most of the pulp. Add one drop of liquid dish soap, and wash the seeds gently to remove the remaining watermelon juice. Rinse the seeds thoroughly with only water. Spread the seeds on a sheet of wax paper. Dry the seeds for one week, turning them once each