Transplant a tree

Occasionally, a client will ask you to move a tree from one place in their landscape to another. This can be one of the most stressful things that ever happens to a tree, and it takes several years for a tree to regenerate a normal root system. In the meantime, the root system will have difficulty supplying enough water for the leaves. Aboveground growth will slow to a fraction of what it was before moving, gradually returning to normal as the root system grows and stress is reduced.

An established tree's root system extends far beyond the branch tips (drip line), with a network of fine roots to absorb water from a large volume of soil. Thus, when you dig a root ball, even one that meets established standards (such as those of the American Nursery and Landscape Association), you can still leave up to 95 percent or more of the root system behind.

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This is an inescapable fact of transplanting, but one that underscores the importance of following proper digging and moving procedures. Let's look at the techniques that help ensure transplanting success.

1. Assessing the situation Root balls are heavy. Before you attempt to move a tree, realistically assess whether you can do so by hand. A tree with a 2-inch-diameter trunk may yield a root ball weighing approximately 250 pounds. However, a 3-inch-diameter trunk can bring the weight up to nearly 700 pounds.

You (and your crew) usually can move root balls weighing up to 500 pounds a short distance on a hand ball cart (see photo, facing page). However, larger plants will require powered equipment. If you and your crew cannot handle the job manually, obtain the necessary equipment or subcontract with someone who can do the job. Attempting to move an oversized tree by hand is likely to lead to failure.

The best time to dig the tree is when it is dormant. The tree is better able to withstand the stress of root loss if it's not also trying to support a leafy crown.

Sometimes it's necessary to move a tree that is not dormant. In these cases, you may need to take additional steps:

* Water the tree thoroughly before moving; * Prune the tree prior to moving to minimize water loss through transpiration; * Store it in a shady place for a few days until it "hardens off"; * Use anti-transpirants, if weather is hot.

Root pruning in advance of transplanting, while the tree is dormant, also is helpful. Usually, however, you won't have enough lead time to use this tactic.

2. Preparing the planting hole After the tree is transplanted, most of the new roots will grow horizontally from the root ball--not downward. On most sites, the new root system will proliferate within the top 12 inches of soil. Therefore, the planting hole should be only as deep as the root ball.

A common mistake is to plant the tree in a hole that's too deep-burying the tree instead of planting it. In fact, in areas where drainage is poor, it may be helpful to have as much as one-third of the root ball extending above the original grade with the soil gradually sloping away. In any case, the root ball should be supported by firm soil underneath to prevent settling. Do not dig deeper and then backfill with soft soil, because this could result in settling.

Creating a hole with sloped or stepped sides (see figure, below) is a good way to focus the digging effort near the surface where the roots will grow most vigorously. This configuration provides up to 10 times more well-aerated surface soil for root growth than a hole of the same volume but with vertical sides. A saucer-shaped hole three times the diameter of the root ball will allow the root system to grow rapidly (within the first year or two) to about 25 percent of its original size before being slowed by the more compacted site soil.

Whether to amend the backfill is a topic of some debate. At one time, experts thought that amending the planting-hole soil could prevent roots from growing outside of the planting hole, so this practice was discouraged. More recent studies have shown that this is not true. However, many experts still feel that amended backfill provides no particular benefit. With or without amended backfill, root growth will slow in a year or two when the roots reach the native soil outside the planting hole, which will be more compacted than the backfill. Digging a proper planting hole--which will provide ample loose soil favorable for root growth--is a much more critical issue than whether you amend backfill.

3. Digging and wrapping Mark the size of the desired root ball on the soil surface around the plant you're moving. The root ball should have about 10 inches of diameter for every inch of trunk caliper. About 4 inches beyond this perimeter, drive a sharp spade into the ground at least 12 inches, cutting all the way around the plant. Then dig a trench outside of this cut at least three-quarters of the depth of the root ball, cutting as many small and medium roots as possible.

With the back of the spade toward the plant, shave off enough soil from the root ball to reduce it to its final, originally planned diameter, with a rounded top edge and uniformly tapered sides (the root ball depicted in Figure 1 is the proper shape).

At this point, you're ready to wrap the root ball with burlap and twine to provide support during transport. It's important to use only natural-fiber materials. Because synthetic materials don't deteriorate, they eventually can "strangle" a plant, causing it to die if not removed.

Wrap burlap pieces around the sides of the root ball, flush with the bottom and extending about 1 foot over the top. To tighten the burlap, pleat the loose folds and pin them securely with nails. Then, wrap the sides and top ("drum-lace" style, as shown in the photo on page 29) of the soil ball with twine to provide additional support.

After the root ball is burlapped and laced, undercut it with a spade. Often, you'll have to tip the tree somewhat to reach the center, which is why you've securely wrapped the root ball first.

One or more people can often lift small root balls from the digging hole. Larger root balls may require a sling or straps. Never lift a tree from the hole by its trunk.

4. Planting Actually planting the tree is quite simple. Carefully place the root ball in the planting hole, oriented so that the tree is facing the same compass direction as before (unless it must face some other direction for appearance's sake). Remove root-ball wrappings from the top and sides prior to filling the hole with soil. Tamp the soil gently to eliminate air pockets, but be careful not to compact it too much.

Stakes, guys and trunk wraps are not required in most situations. Stake or guy the tree only when there is realistic danger of wind blowing it over.

Once the tree is planted, you may want to prune it to get the desired shape and form. Some people believe it is useful to thin the crown to help compensate for root loss. Remember, however, that the tree has lost up to 90 percent of its root system. You won't have much tree left if you prune a similar amount from the crown! Pruning the tree so that it's aesthetically pleasing and has good branch structure usually also provides sufficient thinning of the crown.

5. Aftercare and maintenance * Water. Proper watering is the most important aspect of after-care. Why? In the first year after a large tree is transplanted, it will rely almost exclusively on moisture in the root ball. The tree doesn't have enough roots outside the root ball to absorb water in the backfill soil. Just 2 days after watering, the root-ball soil can become dry enough to stop new root growth and to reduce the capacity of the existing root tips to absorb water even though the backfill soil just outside the root ball may be moist. Frequent soil drying may cause root growth to halt for long periods.

The best way to check root-ball soil moisture is to sample the soil with a soil-profile tube. This tube removes a small core of soil for easy examination. Compress the soil between your fingers. If the soil is not sticky but retains its shape, that's what you're looking for.

To water the root ball, apply water slowly near the base of the plant, or use a root-watering needle under low pressure. For larger trees, you may want to water in several locations over the root ball. The backfill will need little water until the roots grow there.

Be sure, too, not to apply water too rapidly or it will simply run off. You can help prevent water running off the root ball by creating a raised ring of soil at the edge of the root ball (not at the edge of the planting hole; see photo, page 30).

During hot summer weather, the tree will probably need watering at least twice a week. Another approach is to provide 1 gallon of water per inch of trunk caliper daily. This may provide the most consistent soil moisture for roots, but it is not always practical to irrigate on a daily basis.

Although transplanted trees need constant moisture, more is not always better. Overwatering the root ball does not keep it moist longer. The moisture will simply run off into the surrounding soil. It will not move back into the root ball as quickly as the tree is removing moisture from the root ball.

* Mulch. After watering, the next most beneficial thing you can do for a newly transplanted tree is to cover the root ball and planting hole with 2 to 5 inches of organic mulch. This will help keep the soil cool and moist and will provide some nutrients as the mulch decomposes. Of even greater benefit to newly transplanted trees, however, is the protection a ring of mulch will provide against damage by mowers and string trimmers.

* Fertilizer. Many people wonder about fertilizing newly planted trees. As long as there is no nutrient deficiency in the soil, fertilization is unlikely to provide any benefit during the first--and probably the second--growing season.

As the tree develops a larger, more absorptive root system and becomes better established, adding fertilizer will help maximize growth. Research has shown that up to 6 pounds of actual nitrogen per 1,000 square feet of root zone is effective in improving growth of trees once they are established.

Do not, however, use lawn fertilizers containing broadleaf herbicides around trees or shrubs. Some weed killers can be absorbed by the roots and cause injury or death to rapidly growing parts of the plant.

Relatively new root-stimulator products are now on the market, and some individuals who use them report good results. However, existing scientific evidence does not support the widespread use of these products.

* Trunk protection. Post-planting stress can cause the cambium around a small wound to die back farther and become a more serious injury. For this reason, it's important to provide some trunk protection for newly transplanted trees.

To help protect tree trunks from damage by rodents, rabbits, beaver and deer, you can make a cage around the trunk with hardware cloth, chicken wire or metal fencing. The height and weight of the cage depends upon which animal(s) you're protecting against.

Use trunk wraps only when necessary and check them often because they can cause damage. Moisture held under wraps has been associated with bark splitting. Further, trunk guards and wraps, when left on too long, can cause physical damage. In northern climates, it is best to apply trunk wraps for winter sun protection and remove them for the growing season. Conversely, in hot and dry climates, protection from summer sun may be the issue. In this case, be sure to loosenthe wrap at least once during the growing season to prevent trunk constriction, borer activity, excess moisture or canker formation.

Although a growing amount of scientific data is available to guide us in the care and handling of trees, there remains an aspect of it that is more art than science. Experience helps. However, following these guidelines will increase your chances of transplant success regardless of your level of skill.

Patrice Peltier is a freelance horticulture writer based in Colgate, Wis. Dr. Gary W. Watson is a member of the research staff at The Morton Arboretrum in Lisle, Ill., where he is working on root development of trees in urban landscapes. He is president of the International Society of Arboriculture (ISA) and co-author of four ISA publications.

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