Is it possible for vegetables, especially squash, watermelons, pumpkins, etc., to cross in the garden to create a strange fruit?

This question comes up every year. Here's the bottom line on vegetable crossing.

Most vegetables do not cross since they would have to be in the same species to cross. But even if they DO cross (those that are in the same species) it will have no effect on the current year's fruit.
Only the seeds will be affected and this will not show up unless you save your own seeds and plant them the next year. In that case, there may be all kinds off types produced.

FYI, watermelons and squash are in different species so it is impossible for them to cross at all.

The crosses that can occur are some squashes with some pumpkins (if they are in the same species, namely Cucurbita pepo) - there are several other species of squash and pumpkins.

Also, various types of melons (NOT watermelons) can cross. These include cantaloupes, honeydews, canaries, crenshaw, santa claus melons, and persian melons since they are in the same species, Cucumis melo.

Dr. Rick Snyder, Extension Vegetable Specialist