To grow the strongest trees, give them proper care and grooming|In the garden

Published 12:00 am Saturday, January 3, 2009

Trees benefit our homes and cities. They create feeling of relaxation and well being in homes and work places. They add value to residential properties and can help reduce utility bills by 15 to 50 percent.

The net cooling effect of a healthy tree is equivalent to 10 room-size air conditioners operating 20 hours a day. In one year, the average tree produces enough oxygen for a family of four while absorbing the carbon dioxide output from four cars. If every American family planted just one tree, the amount of carbon dioxide in the atmosphere would be reduced by a billion pounds annually. That’s almost five percent of the amount that human activity pumps into the atmosphere each year, according to Trees Are Cool, a program developed by Bailey Nurseries, wholesale ornamental grower in Newport, Minn.

While it is important to plant trees, it is equally important to care for those already growing on your property. During the recent storms, existing trees lost limbs and a few toppled and damaged property. It is important to recognize tree hazards and take appropriate action before the spring flush of growth to insure safety and prolong the life of trees in your landscape.

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The International Society of Arboriculture (ISA), a nonprofit organization supporting tree-care research around the world, is dedicated to the care and preservation of shade and ornamental trees. ISA has some excellent recommendations related to tree care. Pruning is the most common tree maintenance procedure, and ISA says it should be done with the understanding of how a tree responds to each cut. Improper pruning causes damage from which a tree might never recover.

Trees are pruned to remove dead or dying branches or crowded limbs that rub together, to eliminate safety hazards or to increase light and air to the inside of the tree, the tree crown or the ground below. The amount that can safely be removed depends on the tree size, species and age — as well as why the pruning is being done. Younger trees tolerate heavier pruning than mature trees. The ISA suggests an important principle to remember when pruning. A tree can recover from several small pruning wounds much faster that one large wound, and even distribution of foliage-producing sites should always be maintained along the large limbs and lower portion of the crown. A good rule of thumb is to never remove more than one-quarter of a leaf-bearing crown of a tree, and even that might be too much for a mature tree, ISA warns. The older a tree gets, the less energy it has in reserve to recover from wounds and to defend itself from disease and insect damage. Prune large mature trees only to remove dead or potentially hazardous limbs, ISA recommends.

Pruning cuts should be made just outside the branch collar where a limb connects to the main trunk or parent branch tissue. The collar should never be removed. Weight from the outer section of the branch should be cut off first, then the remaining branch stub with the final cut being made just beyond the branch collar. Dressings are not recommended. They rarely speed closure or prevent insect or disease problems.

Some homeowners continue to top trees removing 50 to 100 percent of the leaf-bearing crown, says ISA. This is the most harmful tree-pruning practice possible. The leaves are the food factories of a tree, and this procedure temporarily starves it. The severity of this action triggers a survival mechanism, forcing the rapid growth of multiple shoots to emerge from latent buds below the cuts in order to replace the leaves as soon as possible. Unfortunately this weakens the tree, shortens its life span and might cause it to die if it incurs additional stress from drought, insects or disease. 

Crepe myrtles are sometimes topped. A witty horticulturist came up with a catchy way to warn homeowners not to follow this practice. It has been dubbed “crepe murder.” Branches can be trimmed to remove hazardous areas — but never back to their point of origin. Sometimes, the best solution is to remove a tree if the mature size is too large for a location rather than drastically trying to maintain a manageable size by pruning it.

Trees benefit from regular applications of fertilizer, as do other ornamentals. The Mississippi State University Extension Service recommends an annual application sometime between March 15 and May 30 for mature, well-established trees. For new plantings, wait at least four weeks after transplanting and make a first application in spring — after March 15 and before May 3 — and a second application between Aug. 15 and Sept. 15. A chart is available Apply fertilizer immediately before an expected rain or plan to water the tree immediately after application. Remember that trees suffer during periods of drought and need periodic watering whenever we go through extended periods without rain also.

It takes decades for trees to grow to maturity. Most need little care but provide countless benefits to an abundance of wildlife. Treasure their beauty, feed them annually and modify only when necessary.

Miriam Jabour, a Master Gardener and master flower show judge, has been active with the Vicksburg Council of Garden Clubs for more than 20 years. Write to her at 1114 Windy Lake Drive, Vicksburg, MS 39183.