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Although we may not realize it, many things we do in our yards harm trees and it may be years or decades before the damage shows. Consider the following:
Wrong tree for the site
Often a tree is doomed before it is planted. Because we like a certain species of tree, we plant it even though it cannot tolerate the site conditions. We plant tall trees under power lines or salt-intolerant trees next to roadways.
Trees that need full sun are planted in shady areas. Short and wide trees are planted next to walkways. Poorly drained areas become home to trees that cannot tolerate wet roots. Trees are planted too close together or too near structures. Acid-loving plants are put in alkaline soils.
Before selecting a tree, evaluate the site carefully and be sure the tree you choose is appropriate.
Planting too deep
Roots of a properly planted tree grow down and away from the trunk. If the tree is planted too deep – a common mistake – the roots will grow up toward the surface to get the oxygen they need to survive.
As the trunk increases in size, it may come in contact with the roots growing laterally off the main roots. Eventually the tree is girdled and killed by its own roots. This may not happen for 20 or 30 years, but that's the time the tree is most valuable. Planting too deep can also cause root or trunk rot, internal cracking and crown dieback.
Topping trees is a crime against nature. Often done to reduce the height of a tree for safety, topping – the indiscriminate removal of large branches at a point other than a branch union – accomplishes just the opposite. The stubs serve as entry points for disease and decay. Topping also causes a flush of fast growing sprouts below the cut.
Lawn mowers on the loose
Lawn mowers and weed whips kill more trees than nearly anything else! Be careful not to bang against trees with lawn mowers, or use trees as pivots to spin mowers around. A tree's nutrient and water transport system – its "veins and arteries" – are located just beneath the bark.
Nicking or scraping through the bark will disrupt this system, weakening the tree and making it susceptible to decay. A large nick or scrape can kill the tree. A layer of mulch placed around trees helps control weeds, keeps the roots cool and moist, returns important minerals to the soil – and keeps lawn mowers at a safe distance away from the trunk.
Using broadleaf herbicides or "weed-and-feed" products can damage trees. A tree is a large broad-leafed plant. Products that kill your dandelions or lawn ivy can also impact your tree. Read product labels carefully and be extremely wary about using herbicides around trees.
When a tree looks unhealthy, the initial response is to fertilize it. If a tree is under stress because it is fighting off injury, disease or insects, it must tap its energy reserves for defense.
Fertilizer, especially nitrogen, causes the tree to grow more leaves faster. The energy that should be used for defense is redirected to growth. An overfertilized tree may be susceptible to disease and is in danger of using up all of its remaining energy reserves, leading to faster decline or death.
While new leaves will return energy to the tree through increased photosynthesis, it may not be soon enough. Learn what is wrong with the tree first, and then take appropriate action. Never fertilize before finding out what minerals are lacking in the soil and what effect the fertilizer will have on the tree.
Guying and wrapping
Most trees come with wrapping material around the trunk to protect the tree from damage during shipping, as well as labels indicating species, size, cost, etc. All of these materials should be removed before the tree is set upright in the planting pit.
Never leave any foreign material attached to the tree after planting. Normally, only bare root trees and those planted in very windy locations need to be supported with guying become well anchored. All guying material should be removed, after one year.