zucchini rotting

Question

My zucchini plants always start producing fruit, then when about 3-4 inches long start rotting from the tip down.

Answer 1

It sounds like you are having pollination issues. When the flowers are not properly pollinated, the plant will reject the fruit while they are just a few inches long. You may need to hand pollinate. This article will help:
https://www.gardeningknowhow.com/edible/vegetables/squash/pollinate-squash-by-hand.htm