Separate Beds for Squash and Pumpkins
If you want to harvest your squash or pumpkin seeds for sowing the following year, avoid growing more than one cultivar in the same garden, otherwise it is certain that they will cross. Therefore, when you sow the seeds harvested from a zucchini that grew next to a spaghetti squash, they won’t produce a zucchini new year, but something in between. Always separate the different kinds of squash at least 115 feet (35 m). In other words, in a different garden entirely
At least, that’s the simple explanation. There are exceptions. It turns out some squashes belong to other species, such as the “giant pumpkin” (which is not a true pumpkin at all, but a giant squash, Cucurbita maxima) and the butternut squash (C. moschata) and they cannot interbreed with the typical squashes (C. pepo). In that case, proximity isn’t a problem. However, the vast majority of both summer and winter squashes, including true pumpkins (field pumpkins), zucchinis, spaghetti squashes, crooknecks, acorn squashes, delicata squashes, and vegetable marrows, although they differ greatly in size, shape and color, belong to the species C. pepo and will therefore easily cross if planted close together.