Unripe plums falling from tree
Any reason the the unripe plums on our are falling off, Tree is around eight years old. Roger
Certified GKH Gardening Expert
There can be numerous reasons why a plum tree drops its fruit before it ripens: insects, disease, high winds, and stress ( too much water, too little water, lack of nutrients, poor drainage, weed competition, and excessive shade). But the most common reason -- especially when, as you say the tree is heavily laden -- is that the tree has produced more fruit than it can support. If this happens again, you'll want to thin the fruit.
When the fruit reaches about 3/4-inch in diameter, pick off extra plums so that the ones that remain are about 4 or 5 inches apart.