There is no reason to plant them far away from each other as long as you are not saving seeds. It is sometimes believed, erroneously, that the plants will cross-pollinate and you will end up with some sort of bizarre fruit from that cross-pollination in that garden that year. That is not true.

Squash, zucchini, cucumbers and melons all are members of the Cucurbitaceae family. They all produce male and female flowers and in order for pollination/fertilization to occur, insects, usually honeybees, (or humans who intervene with hand-pollination) must carry pollen from the male flowers to the female flowers. Most if not all members of the Cucurbit family do accept pollen from one another. However, no matter what pollinates the female flowers in the current year's garden, they only produce the correct fruit for their type. A yellow crookneck squash plant won't produce a cross-pollinated yellow crookneck-watermelon, for example, no matter what kind of pollen is deposited on the female flower. So, for the current year's crops there is no worry whatsoever.

The issue arises if you are wanting to save seeds from the fruit to use for planting in the future. In that case, you have to either isolate the various plants with distance or bag the blossoms so insects cannot deposit pollen on them. In that case, when the blossoms open you would remove the bag and hand-pollinate the flower yourself, the put the bag back on it immediately to keep insects from cross-pollinating it that day.

The traditional recommendation for seed savers for these plants is to separate them by 1/2 mile. However, many seed savers have found the distance does not necessarily have to be that great. The easier way is to bag the blossoms you want to save seed from and hand-pollinate them yourself.

If you want to save seed from plants, be aware that you need to leave the chosen item on the vine long enough to reach full maturity. For example, if saving seeds from a cucumber you bagged/hand-pollinated, you'd have to leave the cucumber on the vine far, far beyond the stage at which they're normally harvested for eating. You'd leave that cucumber on the plant until it turned yellow and then almost orange. Usually you will have good seeds in hand-pollinated cucurbita fruit about 3 weeks after you did the hand-pollination procedure. If you harvest the seeds while they are immature, they either won't germinate or may have just spotty germination or may germinate but produce weaker, less virgorous plants. The drawback to leaving your hand-pollinated fruit on the plant to reach full maturity is that your plants will set less fruit. Why? Because the maturing fruit sends the plant a signal it has reached its goal of perpetuating its species by creating seed, so the plant can "relax" and not work so hard to produce more seed.

So, if you aren't wanting to save seed, plant away per your original plan and don't worry about it. If you want to save seed, bag the blossoms before they open and harvest only from the blossoms you bagged and hand-pollinated.

I grow all of the plants you mentioned every year in close proximity to one another with no issue whatsoever for the current year in which they are growing.

You should know, though, that they share a lot of the same pests so watch carefully and at the first sign of those pests on one member of that plant family, keep your eyes open for an infestation on the others.

Dawn

WOW!!! Thank you. That answered that and more. I think I have a LOT more to learn before I begin the process of saving seeds. I am still learning. I am also now keeping a journal with diagrams in the hope that I will actually begin to make progress from year to year.

You're welcome.

For what it is worth, I am in my 50s and have been gardening all my life, and I am still learning too.

The more you learn, the better your plants grow , and I hope I never stop learning. To me, gardening is endlessly fascinating, and if you are not learning something new from gardening or about gardening on an ongoing basis, then you're doing something wrong.