The American Plum tree is native to North America, growing throughout the eastern and western United States and wild across the state of Ohio. It produces white fragrant flowers in early spring, following with edible fruit in the summer. American plums are sweet but extremely tart and are best used in preserves, jams and jellies. They are ready to be harvested in mid or late summer. According to Ohio State University Extension specialists, September is the recommended time for harvest.
Look for a vibrant, red color on the fruit. The plum may have a slight yellow hue to it as well, signaling maturity. The folks at Ohio State University Extension, say that the color will change drastically as the plum approaches the final stages of maturity.
Squeeze the fruit. A ripe plum will have a slight give under pressure, but still maintain a firm feel.
Taste the plum. As fruit ripens, its sugar content gradually improves. Plums will ripen after they are picked, but tasting the fruit is a good way to test if the fruit is not yet ready to be harvested. American plums are tart by nature but still should be fairly sweet when ripe. Extremely tart or bitter fruit still needs time to mature.
Pick each plum by hand. Never allow a plum to fall to the ground as the fruit may become bruised or the skin will break.
Pick the plums that have ripened to your desire and leave any that are not quite ripe enough. Once a few plums begin to ripen, the others will follow throughout the week. Check the tree every two days for more fruit.
Store picked plums in the refrigerator, where they will keep for one week. To preserve the plums for up to a month, store them in the freezer at 30 to 32 F.