Plants on the Move

Master gardener Paul James gives tips on transplanting trees and shrubs.

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Digging up plants and moving them to another location often strikes fear in the hearts and minds of gardeners. But there's really nothing to fear, says master gardener Paul James.

He focuses on woody plants, specifically deciduous shrubs and small trees. Winter, when the plant is dormant, is the best time for moving. "Growth at this stage is at a virtual standstill which means the risk of transplant shock is next to nothing," he says. "If you were to wait until the plants leaf out and are actively growing, the risk of transplant shock goes way up. And that means the plants may not survive the process."

Paul's favorite time to move woody plants is late winter or early spring, just as the buds begin to swell. The swelling buds are the first sign of growth on the upper portion of the plant, and in another week or so, the roots will begin to grow as well.

How big a root ball should be dug? "The short answer is, the wider the better — or, as big a root ball you can lift."

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Paul James uses "the rule of 18" to determine the ideal size of the root ball.

Paul has a simple formula that will help you determine the ideal size of the root ball: Measure the trunk one foot off the ground. Then, measure the caliper (diameter) of the tree at that point and multiply that by 18. The number you get is the diameter of the root ball that should be dug.

In the case of a young weeping cherry that Paul wants to move, the caliper is just one inch, so he needs a root ball with a diameter of 18 inches.

With shovel in hand, Paul digs the tree up, slicing through the soil and roots at a slight angle towards the base of the tree. He lifts up with the shovel as he works to free the roots.

How far down should he dig? "Unfortunately, there's no simple formula," says Paul. "However, the vast majority of a plant's roots reside in the top 12 inches of the soil, so it isn't really necessary to dig deeper than that, especially in the case of a small tree like this. In fact, even in the case of a much larger tree, one that's twice this size or more, I wouldn't dig down more than 18 to 24 inches."

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To make the transition as smooth as possible, Paul recommends digging the new planting hole first. By digging the planting hole in advance, the roots of a newly dug tree won't dry out while the new hole is being prepared. Roots left to dry out may not survive the transplanting process. If you're forced to wait — even a half hour or so before transplanting — make sure you wrap the root ball with several layers of moist newspaper or some burlap so the roots don't dry out. "And if the soil falls away from the root ball, that's okay," says Paul. "It will give you a chance to tease the roots a bit."

Transplanting a tree is identical to planting it. Gently place the roots in the planting hole, and add enough soil to stabilize the tree to make sure it's straight. Fill the hole with soil, tamping it down as you go. Leave up to one-third of the root ball above ground. Then water well, and apply a 2-inch layer of mulch around the root ball but avoid filling in mulch all the way up to the trunk.

According to Paul, if he were to dig up this dogwood using his formula for the ideal-size root ball, the weight of the root ball on the tree would be well over 500 pounds, perhaps up to 700. A job like that is best left for the professionals. But virtually any tree can be moved, including one that's 10, maybe even 20 times the size of that one. Of course, it takes special machinery, skill and lots of money.

Although a fothergilla is perfectly healthy in Paul's landscape, surrounding plants have caused some crowding. As a result, it's growing in a lopsided fashion, so he decides to move it. "In the case of multi-trunk shrubs like this, there aren't any hard and fast rules about how wide the root ball should be." Basically, you should assume that bigger is better — that is, of course, if you can handle the weight.

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Again, Paul has already prepared the new planting hole. And Paul plants it just as he did the other tree.

There's some controversy as to what you should do next. "Some experts think you should remove as much as one-third of the top growth of the tree or shrub to compensate for the loss of root during the digging process, and I tend to agree," says Paul. "However, I suggest you take those cuts from the interior of the plant rather than heading back the entire plant by one-third. That would destroy its natural shape."

The same techniques and timetable work for evergreens, too.

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