First, decide if you can handle the job. It isn't easy. The project requires root pruning the season prior to transplanting, digging up the plant to be moved, digging a new planting hole, moving a heavy plant with the root ball attached, positioning the plant and refilling both holes. Providing plant care after the transplant is critical as well. Do not consider transplanting if you will not be able to provide water for the plant for at least the first year after transplanting.
Make sure the tree or shrub is a manageable size. Shrubs up to 3 feet tall and trees an inch or less in diameter (measured 6 inches above the soil level) can be moved without digging a solid root ball. These and most plants 3 to 4 years old may be moved as bare root transplants. Larger or older plants will need to be dug and transplanted with the root ball intact.
For a transplant to be successful, you must include as much of the plant's root system as is reasonably possible. In general, you'll need at least 10 to 12 inches of root ball diameter for every inch of trunk diameter.
Example: If a tree is 3 inches in diameter, you will need a root ball that is 30 to 36 inches in diameter.
The depth of the root ball also increases proportionally. Include as many of the lateral roots as possible. Since these roots are near the soil line, a root ball that's generally 12 to 24 inches deep will include those roots.
A root ball with soil and plant attached will weigh about 100 pounds per square foot, so have the necessary machinery or manpower available to move it. The bigger the tree, the less likely a do-it-yourselfer you will have a successful transplant.
Fall, late winter or early spring are the best times to transplant. The move should be done after leaves fall in the autumn or before new buds break in the spring. If you are in doubt as to the best time to transplant in your area, your local Cooperative Extension office is a valuable resource.
Good to Know
Very large landscape plantings can be moved with a truck-mounted hydraulic tree spade. Depending on the size of the machine, trees up to 50 feet tall can be successfully transplanted. You will need to find a professional to do this for you.