There are three basic types of plums, Japanese, European and hybrids. The Mount Royal plum tree is a European type, and the fruit is suitable for drying and making prunes. Mount Royal is a very hardy, very dark blue freestone fruit. The fruit is sweet and juicy and is the most common used in home gardening. The tree can grow 10 to 14 feet with a spread just as large. Being self-fertile, you don’t need to plant another tree nearby for pollination. Mount Royal plum trees are hardy in USDA planting zones 4 through 8.
Water the Mount Royal plum tree at least twice a week throughout the first growing season. During hot, dry periods, increase watering times so the tree does not go through water stress. The first year is critical for good root system production; never wait until the leaves start to wilt.
Place a two-inch layer of compost in a two-foot diameter around the tree. Normal watering will leach it into the soil. This will give the tree some nutrients to start off the season and keep the soil draining well. Repeat each spring.
Spread a four-inch layer of organic mulch, such as wood chips, in a three-foot diameter around the tree. Keep the mulch at least two inches away from the trunk. The mulch will retain moisture and keep weeds from growing around the tree. Renew the mulch each year as it decomposes.
Fertilize Mount Royals with a balanced fertilizer only if the tree is not vigorous and growing. If branches did not grow at least eight inches from the previous year, then apply the fertilizer. Too much fertilizer can do more harm than good with stone fruits. Follow manufacturer’s directions for the amount to apply.
Prune the tree to train and shape in early summer the first year and early spring from then on. Cut the central leader to 12 inches the first year if it is larger. Choose six evenly spaced branches around the trunk for the scaffold branches and cut the rest off. In the second year, leave two tier branches on each scaffold branch and cut the rest off. This will give you a good form to the tree. From the third year on, cut off dead, damaged and diseased branches and trim only as necessary to keep the shape.