The best time to plant a plum tree is either in early spring or fall. Planting at this time gives the tree time to take root before there are extremes in temperature--the intense heat of summer or the cold temperatures of the winter season. You can purchase plum trees from the nursery either in containers or balled and burlapped. When you plant a tree that comes in a container, remove the tree and root ball from the container before planting. With balled and burlapped trees pull the burlap halfway down the root ball before planting. You do not need to remove the burlap completely as it will disintegrate after you plant the tree. However, if the tree is balled and wrapped in plastic, remove the plastic completely. (Generally, older trees come balled and burlapped.)
Read the characteristics of the species of plum tree that you have purchased. You need to understand the space requirements of the tree, specifically how high and how wide it will get when it reaches maturity. Choose your planting site, allowing enough room for the tree to grow. Also, make sure that the site is in full sun--plum trees require full sun.
Dig the hole. The width of the hole needs to be twice the width of the root ball. The depth of the hole should be as deep as the height of the root ball.
Pile the dirt that you dig out of the hole close to the hole. You will be using this dirt to fill the hole once the tree is planted.
Place the plum tree in the hole making sure that it is in a straight, upright position. You do not need to amend the soil as plum trees tolerate most soils.
Put the soil back into the hole and tamp it down lightly. Be sure to break up any clumps of soil with your garden fork.
Build a berm of soil around the perimeter of the hole and fill it with bark. The berm should be approximately 4 inches tall. The bark will keep moisture in and weeds down.
Fill the berm with water. You need to continue to water the tree lightly on a daily basis for the first week after planting.