Transplanting a purple smoke tree (Cotinus obovztus) is not difficult if you know when to begin and how to care for the root ball as you remove it from the ground and transplant it in another location. The best time to begin this process depends on when you want to transplant the smoke tree. A good way to determine when to begin the process is after the deciduous trees lose their leaves, or before the buds begin to break in the spring.
Root-prune by inserting a spade or shovel into the ground, going all the way around the tree. The distance from the trunk to where you need to make your root-prune depends on the height of the tree you are planning to move.
If it is 2 feet high, keep the circle in a 12-inch diameter and dig down to a depth of 9 inches. For a smoke tree that is 5 feet high, the root ball should measure 18 inches in diameter and you should dig to a depth of 14 inches.
If you plan to transplant the tree in October or November, root-prune in March. If you are planning to transplant in March, root-prune the smoke tree in October.
Prepare the place where you want to transplant the smoke tree. Dig the hole close to the same depth as your transplant, but make the hole twice the width. Remove the soil and mix it with some compost. Fill the hole with water and allow it to drain out naturally.
Dig up the smoke tree, keeping the root ball intact as much as possible. Place the smoke tree's root ball into the center of the hole you dug. Finish filling in the hole with the amended soil.
Tamp the soil in place to remove the air pockets. Water thoroughly.
Place a 2- to 3-inch layer of mulch around the smoke tree. This will help keep the moisture in during the summer, and help protect the roots during the winter.