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If your plums have their

If your plums have their first flush of color, they should ripen off the tree. Pick them and put them on a flat tray in a cool room for a few days and they should ripen up. In the future, if you want to keep this tree, you need to prune it and also thin the fruit when young so it's less loaded down. For plum trees, you want to thin in April/May when the fruit is about 1 diameter and about 2 to 4 inches apart.