Cherry plums are

Cherry plums are traditionally not thinned. In terms of harvesting, they have a long range for ripening, so you really just need to look at the fruit. It's best to wait until they are fully mature, but before they fall from the tree. The best way is to take a couple samples and taste test! The fruit will become softer and the flesh will become juicier and sweeter. Often, it's the birds who will know and pick you clean! Netting is usually the best way to deter birds.