Summer squash like bush winter will average approximately 4 mature fruits per plant. It is best to allow fruit from the crown set to mature for best results. Each mature squash contains a lot of seeds. Usually enough summer squash get away from you to provide plenty of seeds. They are promiscuous tho and you have to work to get pure seed.

Thank you, farmerdill! Can you clarify what you mean by: “It is best to allow fruit from the crown set to mature for best results”? I couldn’t find info on what “crown set” means specifically. And I don’t have any other C. pepo varieties growing in my garden, so I can assume these to be pure seeds, correct?

"Crown" set is the heavy first set on new vines. Usually the most abundant set close to the root of the vine before the vine grows enough to sprawl. The idea is to get the number of fruits you wish to mature growing at the same rate. One fruit maturing will drain energy from later setting fruits and may cause them to abort. As long as you don't have C. pepos growing within a quarter mile you should be ok saving seeds.

"As long as you don't have C. pepos growing within a quarter mile you should be ok saving seeds."

Agreed - but just to expand on that. C. pepo is probably the most widely grown squash species. Besides most summer squash, it includes acorn squash, spaghetti squash, hard-stemmed pumpkins, and warted gourds. The flowers are exceptionally good pollen sources, so bees will fly a great distance to feed on them.

To put this in perspective, I was saving seed from an acorn squash in my rural garden, with no other gardens in sight (for about 1000 feet). When I planted that seed the following year, about 25% of the plants were crosses... apparently with a pumpkin, and with a yellow summer squash. That was in a rural area; in an urban or suburban location, crosses would be even more likely.

Oh, and a squash saved for seed requires a long time to mature - until it changes color, which is about 2 months or more. I concur with Farmerdill's recommendation of letting the crown set go to seed. Because of the large number of seeds produced, it might be best to allow a single plant just for seed, and harvest summer squash from the remaining plants.