Rick Shilling, of the Smithsonian Institution, prepares an overgrown Japanese maple for transplanting from the Ripley Garden. Part of its retaining wall was taken down for the move. (Janet Draper/Courtesy of the Smithsonian Institution)

Ornamental trees and shrubs can outgrow their allotted space or find themselves in the way of a new patio or addition. By relocating a prized plant, the gardener can not only save a tree but also provide a great focal point for a reworked area. Several factors determine whether to move a tree or shrub — the beauty and age of the plant, its sentimental value and its chances of survival if moved — but one aspect carries the most weight: the size.

The do-it-yourselfer can probably dig and move a tree with a 11 / 2-inch-thick trunk, or a shrub or evergreen of about five feet high, said Dave Reed, vice president of Meadows Farms landscape and nursery company in Chantilly. Double the size and you will need “three or four strong people” to shift the excavated plant because of the weight of the rootball, he said.

In the fall, conditions lend themselves to what landscape companies call “on-site transplanting.” This is more than just a job for strong backs; you have to follow rules or risk killing the tree, evergreen or shrub. Here’s our primer.

How do you lift a tree?

There are two basic methods. The rootball can be dug by hand or excavated with a serious piece of equipment called a hydraulic tree spade. Tree spades are used for larger trees, though sometimes a big tree has to be dug by hand because of site conditions, in which case excavation will cost more than with a tree spade. Gardeners at the Smithsonian last month hand-dug an approximately seven-foot-wide rootball of a weeping Japanese maple and replanted it several hundred feet away, on the west side of the Freer Gallery of Art. The liberated tree had outgrown its space in the nearby Ripley Garden.

Does size matter?

Absolutely. The larger the transplant, the heavier the rootball, the greater the effort and the more likely the need for special equipment to dig and move the plant. Reed said his crews hand-dig rootballs up to about three feet across, beyond which they have to resort to a tree spade.

How do you measure a tree?

For deciduous trees, you measure the trunk’s width — or caliper — at six inches above the ground (for trees with up to a four-inch caliper). A two-inch-caliper specimen is a fairly large young tree. A four-inch-caliper tree is exponentially larger and heavier. For shrubs and broadleaf and needled evergreens, the digger takes into account the height of the plant in gauging the size of the rootball.

How do I know whether to move a tree or shrub?

First, ask whether the plant is worth saving. An old English boxwood, an ornamental cherry and a weeping Japanese maple are obvious treasures, along with any choice, slow-growing specimen. A fast-growing and common plant such as a Leyland cypress, arborvitae or Bradford pear wouldn’t be worth the expense, especially if it is getting big.

Transplanted trees, as a rule, are not guaranteed to live, making the cost of planting a new tree, with a warranty, more economically feasible.

David Watkins, of Merrifield Garden Center in Merrifield, offers this advice: “If it’s under two inches, it makes sense. If it’s between two and four inches, it becomes fairly questionable to move it versus buying a new tree.”

What are the dimensions of the rootball?

The correct size of the rootball is directly related to the tree’s height or girth. The sizes are standardized in industry tables, but a rule of thumb is that the rootball should be roughly one foot wide for each inch of trunk caliper.

How much does a transplant weigh?

The 15-inch-wide rootball of a young holly or viburnum might weigh as much as a grown man. The Smithsonian’s transplanted maple weighed an estimated 5,000 pounds.

How important is site accessibility?

Poor access can be a deal breaker, especially if mechanical equipment is needed: A contractor will need room to maneuver a tree spade as well as a clear path from the old location to the new one. Steps, structures, gates and other landscape elements can create serious barriers. Steep slopes present other challenges. If you have terrible site access but deep pockets, you can move a tree with a crane, an option that typically costs several thousand dollars.

What are the considerations for replanting?

A plant that prefers a little shade — a boxwood, rhododendron or hydrangea, for example — should not be placed in a new location that is either too sunny or too dark. Sun-loving plants moved to a shadier site will see flowering diminish. Soil pH can vary within a property, but the more likely soil problems will relate to drainage. Moving a plant to an area that stays wet can spell doom. And make sure there are no buried pipes or electrical lines before you start digging.

In the move, you might need to protect branches and reduce the width of the tree by carefully wrapping the vegetation in burlap.

Dig the new hole before you start excavating the plant. Match the hole’s depth to that of the rootball: The plant must not sit too low in its site, and once you drop it in, you won’t want to lift it out again.

What tools and other equipment will I need?

If you are hand-digging, you will need as a minimum a strong spade and a mattock for prying stones and slicing roots. Probably no one hand-digs more trees in these parts than Tom Moseley, who runs Maryland Gardens Tree and Shrub Farm in Potomac. Moseley uses a short digging spade with a steel reinforced shank, called a full strap nursery spade.

.I would also have handy a digging fork to deal with buried stones and an ax to sever roots. You might also want a long bar for digging and prying, called a spud bar. This is used for breaking the rootball free from the ground and for general maneuvering. You might also need a large dolly called a ball cart, for moving the transplants. Equipment rental centers have carts.

It is important to keep the soil in the rootball intact, to minimize root trauma. You might be able to place a transplant on a tarp and drag it to its new site, but if it is going to get jostled, you should wrapthe ball in burlap. Burlap comes in sheets or in rolls, and is pinned with nails and tied at the top. For extra security, some gardeners secure the burlap with rope circles at the top and bottom of the ball, which are then drum-laced together. After replanting, free any ties and ropes that might interfere with trunk growth and let the burlap rot in place.

What care does a transplant need before moving?

First, the soil around the tree should be deeply soaked to hydrate the tree and to make digging easier.

The best transplant insurance is a technique called root pruning. Several weeks or, preferably, months before the move, make an encircling slice through the soil and the roots — drive the spade as deeply as it will go at the correct distance from the trunk. Then leave it. In time, the severed roots will grow a tight mass of new feeder roots that will lessen the stress of the eventual move.

If you want to be a perfectionist, you can dig a six- to eight-inch-wide trench outside the sliced roots and backfill it with organic matter to promote a robust root regeneration. Moseley uses his own mix of equal parts rotted horse manure, composted leafmold and sand.

October is a great time to do this (we’re in root-growing season) for a tree that will be moved next February or March.When you dig the rootball for moving, it is vital, of course, to dig beyond the initial slicing to retain the new root growth.

Although root pruning is not always necessary, it’s highly recommended in advance of transplanting in the growing season, especially in the hot summer months.

What care does a transplant need after moving?

The same basic care as a tree that came from a nursery instead of across the back yard: The base of the trunk should sit an inch or two above the soil line, and the transplant should be well watered but not soaked constantly so that it drowns. A light mulch will help, but avoid mulch “volcanoes” that smother the trunk. The tree or the rootball might shift over the winter and should be reset after the ground thaws. Tree stakes might help.

Are some plants easier to move than others, even if they are the same size?

Small shrubs with fibrous surface roots such as azaleas, blueberries and boxwood can be moved like furniture. Moseley reports a lot of success with fruit trees, maples, lindens, crape myrtles and most conifers, though a Leyland cypress has a small root area compared with its top growth and will move in winter winds after transplanting. Many common shrubs are easy to dig up and relocate, including lilacs, weigela, nandina and forsythia. Taprooted trees such as redbuds and blackgums are harder to transplant. Oaks are also deep-rooted and require a deeper rootball. The white oak is notoriously difficult to move.

What time of year can a tree be moved?

Pretty much any time will work, with preparation, but it’s less risky to do it when the plant is most amenable. Reed likes to halt fall transplanting of evergreens after Nov. 1, because transplant shock and frozen soil don’t mix — the evergreens actually can dry out in winter winds. Deciduous trees and shrubs can be moved now until late November. Some trees don’t like to be moved in the autumn and should be moved in early spring, including oaks, redbuds and river birches. Hickories, filberts and other nut trees generally don’t like to be moved at all, Moseley said.

Can I “store” a transplant for replanting later?

Yes, but the tree should be held in a shady and sheltered location and the rootball must not dry out. You can cover the rootball in leafmold, compost or even woodchips — or heel it in to a spare patch of ground. Check periodically while watering to make sure the rootball is not exposed.

What is the cost?It depends on the size of the tree and site conditions. Reed said the straightforward transplant of a 11 / 2-inch-caliper Japanese maple should take a crew less than two hours and cost about $200. Moseley said he charges a minimum of $300 for a crew to hand-dig and $500 if he has to arrive with his tree spade.

Watkins said a tree-moving crew might cost $400 to $600 or more, but he often tells a homeowner that with fewer guys and no rootball wrapping, “I can just pop it out of the ground for $100, $200, and if it makes it, great, and if it doesn’t, it doesn’t.” Fall would be the time to try that.

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