Squashes are a part of the Cucurbita family. Within the Cucurbita family there are like five different species of squashes. If you grow two varieties of the same species within a quarter-mile of each other, they will likely be cross-bred resulting in seeds that can not be used for any further generations.
If you pay attention and only grow one variety of each species, then you can grow five different varieties of squashes without concern for them cross-breeding.
If you pay attention and only grow one variety of each species, then you can grow five different varieties of squashes without concern for them cross-breeding.