How do I keep my zucchini plants from rotting at the base?

Could be several things. Here are some sites with possibilities and remedies.

https://homeguides.sfgate.com/zucchini-root-rot-prevention-37517.html

http://www.gatewaygardener.com/pests-and-disease/squash-vine-borer

https://www.gardeningknowhow.com/edible/vegetables/zucchini/solutions-for-common-problems-growing-zucchini.htm

Powdery mildew. Buy a spray to combat it or spray plain milk, yes milk on the entire plant as first sight of the white on the leaves. Pick off the bad ones and coat with milk or the mildew spray. Last year Everybody had a horrible time with it. not just in the garden either. Peonies, lilacs were hit hard as well. On garden plants it kills the vine first and just makes things like lilacs look really ugly but will not kill them. Wash garden tools after use as it is easily spread. Put leaves you pick off in a plastic bag, tie shut and dispose of.

Hi Connie. I'm Cindy. I believe you are dealing with Blossom End Rot. This is the result of inconsistent watering. If there's no water in the soil for the roots to consume, it will begin to rot. And that rotting starts at the base of the plant and works it's way up. You can fix this problem with regular watering and a couple inches of mulch. Also adding sand to the soil when you till the garden up before planting, the sand helps with water retention. Good luck Connie.

If you mean the zucchini plant, you can put foil under it to reflect light and help resist rotting. If you mean the vine, you need a mineral the plant is not getting such as calcium. You can buy "prevent blossom rot" for such needs for tomatoes and I imagine zucchini also. We literally pureed egg shells and put them in the watering can for our tomatoes. The same could be done for zucchini. It has to be fine powder or the plant cannot break it down in one season, so do not just put out crushed egg shells. Here is an article also about what minerals or feed to add: https://www.gardeningknowhow.com/edible/vegetables/squash/squash-blossom-end-rot-causes-and-treatment.htm