Watermelon seeds should be planted in the late spring, early summer or fall. It is best to wait for warmer temperatures since watermelons are considered warm-season plants and do not tolerate freezing temperatures especially during germination. Fall planting is ideal because it gives your seedlings enough time to grow before winter comes knocking on their door. There’s no need to hurry either as you can plant from cold soil, but if you live in a place where the ground freezes each year then waiting until fall will likely make more sense as many gardeners have reported good results with this timing of planting. In any case, only use certified non-GMO seeds that have been through testing for purity and quality control!