Squash are easy to save seed from, but keeping a variety pure can be tricky! Squash have separate male and female flowers and rely on insects for pollination, so different varieties of the same species can readily cross. This only matters if you want your saved seed to grow true to the original variety. If you’re happy to experiment, crossing can be a fun way to create something new!
First, make sure you know the species of your squash. Varieties within the same species can cross. For example, butternut and Seminole pumpkin are both Cucurbita moschata, and therefore can cross if they are flowering at the same time and growing in proximity. Zucchini, acorn, and many summer squash are Cucurbita pepo, and so they all can cross with one another. Different species generally will not cross.
If you want to keep a variety pure, grow only one variety of that species, provide plenty of isolation, or use hand-pollination to control which flowers cross. This is especially important for seed growers because pollinators can travel considerable distances between squash plants.
For seed saving, choose fruit from your favorite fruits with the qualities you like (shape, color, flavor etc.) and allow the squash to fully mature. Winter squash can be harvested for seed when the fruit is fully mature and ready to eat. Scoop the seeds from the mature squash and separate them from the surrounding flesh. Rinse them well, then spread them out in a single layer to dry completely. Once thoroughly dry, store them somewhere cool, dark, and dry.
Learn all you need to know about saving tomato seeds in our free guide: Saving Winter Squash Seed