By Jackie Burghardt, Colorado Master GardenerSM, Colorado State University Cooperative Extension, Denver County
Trees can be considered one of the most natural valuable assets of any landscape. Healthy, established trees can add many thousands of dollars of value to any landscape, be it residential, commercial, or public. They give street appeal to a property, heat when dormant and shade when in leaf, and provide sheer beauty in their fully leafed out canopies hovering over the landscape. We plant them to commemorate births, deaths, marriages, and almost any event possible. We revere them because their towering presence is a reminder of historical events and are intricately linked with our sense of the past. They are our friends in high places. A beautiful tree in the "wrong" place may be salvaged rather than destroyed. Perhaps it is for any or all of these reasons that decisions are made to move established trees.
An established tree, one that has been planted for three or more years, has roots that extend well beyond the drip line of the tree. In fact, conservatively 60-75% of an established trees root biomass is outside the dripline. That means that a fully grown tree can have roots branching out in diameter up to two to three times its height. If all of these roots are important in providing water and minerals and physical support for this tree, it is easy to see that problems can arise when its root system is cut and reduced when it is to be moved. A tree that is 30 tall has accumulated mass (density) as well as height and its weight and size become an issue in transplanting. Davey Tree Co. is a firm that works all over the country moving trees of all sizes. They have successfully completed some of the largest tree moves ever, ones with transplanted root balls exceeding 40 in diameter and weighing more than 1 million pounds. Thats roughly equal to 225 Chevrolet Suburbans.
So what are some concerns that should be considered in moving a tree and what happens to it as it is moved?
The overall physiological changes that affect a tree through moving it are relatively alike regardless of the size or age of the tree. The size and condition of the root ball in relation to the overall size of the tree is a factor in the amount of stress a tree will realize when it is moved. It is important that a tree be moved to a receptive environment. Ambient air temperature, humidity, and wind velocity will affect water loss in the tree. The soil environment into which the tree is planted is important for root growth. We come to the root of the problem.
The larger the root ball, the better the chance for success for the tree in its reestablishment. It is important to keep the integrity of the root ball intact to avoid transplant shock. A large portion of the food lifeline is being left behind. The stored reserves in the roots will get a tree through its first year, so if the roots are not properly transplanted, the tree will die. The American Association of Nurserymen has set standards for root ball moving. A minimum standard is eight inches of root ball for each inch of trunk caliper for needled evergreens and nine inches of root ball per inch of trunk caliper for deciduous trees. A caliper is measured six inches above ground.
Root pruning is a practice adopted by many tree movers and nurseries selling ball and burlap trees. The roots are purposely trimmed back to lateral roots that respond by producing more roots, thereby increasing the size of the root ball and encouraging growth of smaller root hairs. This practice can be done purposely in any setting where a tree is to be moved and there is time to increase root growth before its move. (There is a specific procedure for this practice, but it is not discussed here.) The benefit is an increase in the integrity and volume of the root ball making for a tree, when transplanted, that should acclimate very well to its new surroundings, given proper post-transplant care. This practice can be helpful on smaller trees. For larger trees, this idea is controversial. Some think that when using a larger spade to dig up a tree, such as 90", root pruning may not be necessary because a larger portion of the roots is being salvaged with the tree. A 90" spade usually relates to a 14" tree caliper.
When the roots of the tree are cut by a spade or shovel in preparation for a move, a once large system of roots that fed the tree is now reduced immensely. For a tree in leaf, this huge reduction in the availability of minerals and water through the root system to the leaves is stressful as the tree struggles to maintain its existing growth with a much reduced feeder system. It is put on a forced diet. The leaves rely on water and minerals that moves from its roots up through the xylem. Sunlight is processed by the leaves in photosynthesis, which creates sugars that return down the tree through its phloem to feed the roots.
Rebuilding the root system is necessary to restore the feeding system of the tree so that all of the vegetative growth above ground level, the trunk, branches, twigs, leaves, and flowers, are able to function and survive. During this period of growth by the roots, the tree produces very little new vegetative growth. A dormant trees roots are less affected than a tree in leaf is by the shutdown in photosynthesis, and prevailing opinion is that for a deciduous tree, it may be moved when in leaf or dormant. Spring planting gives a tree a full season to acclimate to its new environment and prepare for the cold winter season; however, dormant planting allows the tree to be moved with less consequence to roots and existing foliage. Conifers also can be moved at any time except when they begin candling. A timetable for the reinstatement of the trees growth above ground follows a general rule of thumb: one year for each inch of trunk caliper.
Root stimulant has been shown to be helpful in encouraging vigorous root growth, and one tree mover believes it is the most important thing you can do in reestablishing a tree. His practice is injection of mycorrhizae or phosphate for two to three years after transplanting. Some root stimulants contain mycorrhizae and there is controversy as to whether these are more helpful to one particular species of tree than another, or helpful at all. If a large portion of the root ball is transplanted with the tree, any mycorrhizae contained in that root ball will obviously continue to help the root system grow back to maturity. Current research underway at Colorado State University hopes to answer at least part of this question.
Since the tree must be able to redevelop its root system quickly, the soil conditions need to be optimum for new root growth and should at least closely approximate those of its origin, or be improved beyond that with the addition or organic matter. The climate of the soil, its porosity or oxygen, clay or sand content can make the difference in whether a tree survives a move or not. The roots need oxygen as well as water and minerals from the soil and this relationship of oxygen in the soil and regrowth of the root system is the most important consideration in transplanting.
Transpiration of water on the leaf and stem surfaces will cause the stomatas guard cells on the undersides of the leaves to close to protect water resources; if sufficient watering of the tree is not maintained, as a result, the leaves curl, dry up, or die. This means that photosynthesis cannot take place and those sugars feeding the roots are not produced for their necessary growth and development. Antitranspirants can help reduce the water loss from tree foliage. The most common forms are film formers, which are sprayed as a mist on the leaves, lightly coating them with a waxy or oily substance, reducing transpiration. A misty application is key to their success and is most beneficial when trees are in full leaf. The transpirants last approximately two weeks. An overdose or too-heavy application can cause photo toxicity and suffocation.
After a tree has been successfully moved, maintenance and care are crucial in assuring its reestablishment and long life. It is imperative to keep the roots watered regularly so they maintain a moist root ball and are not allowed to dry out, but not kept so wet that they drown. Lack of proper water or over watering is the number one reason moved and transplanted trees fail to thrive. Environmental and soil conditions will regulate how frequently watering should be done. One tree mover is adamant about the use of insect spray after transplanting in helping the tree ward off invasion by pests that can reduce its viability.
Pruning of active growth of the tree before, during, or after a move should be avoided for three years, the approximate time it takes for the roots to rejuvenate. When a tree is pruned, it releases hormones, or auxins, that encourage new growth at lateral buds along the branches. Normally, feeding this new growth would not be so taxing to the root system, but it is problematic for a newly moved or transplanted tree because it is struggling to maintain its current vegetative growth while at the same time renew its root system. One study found that pruning of terminal buds of sugar maple seedlings delayed root growth until another bud developed. In another test of bare rootstock of 6 tree species, nearly all trees survived the post-planting pruning, but none benefited from it. Of those pruned, 30-45% did not reestablish a natural growth form. Removing deadwood, however, is helpful to remove opportunities for pest and disease to attack the tree, and its removal bears no consequence to the root system.
Trees may be appraised for a dollar value based on their species, condition, size, location and other factors. Trees have very real worth and greatly improve the quality of our lives.
Photos courtesy of National Shade, A Davey Company
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010