Given the impact that shade trees have upon the home and/or landscape environment, paying attention to their needs is a worthy task.
I’ve encountered many who believe that taking care of a tree is as simple as making sure not to hit it with their truck, but proper care can be a bit more involved.

Though not as maintenance demanding as a fine lawn, trees do have needs that are often neglected in a landscape environment. Attention to those needs is often the difference between the proliferation and sustainability of a tree, versus its decline.

One need that is often overlooked is the correction of soil compaction problems, resulting in reduced levels of soil oxygen which is needed to maintain roots.

Compaction reduces soil oxygen for as soil compacts, the oxygen containing pore spaces between soil particles are crushed.

When oxygen within the root zone falls below a threshold level, roots and subsequently, above ground portions of the tree will decline. If, on the other hand, abundant levels of oxygen are available within the root zone, roots and above ground portions of the tree will proliferate, provided other needs are being met as well.

Soils within an urban environment tend to compact for a variety of reasons. For one, sturdy construction requires adequate soil strength, which in turn requires packing the soil. Therefore, soil adjacent to construction of any sort has likely been intentionally compacted, to one degree or another.

Soil compaction also occurs as leaves and other organic matter, which buffer compaction by a natural means, are largely removed from the landscape long before time needed to break down and become part of the soil profile.

Also, soil compacting foot and equipment traffic commonly occur and contribute significantly to the problem.

Though some compaction problems are complicated such that the help of a good arborist should be sought, others can be lessened by anyone willing to apply needed treatment with care.
Just as a lawn can be aerated, so can a tree. The process is just a bit different and requires a different set of tools.

One means that tree care companies use to aerate soil, is to drill a series of holes, three to four inches in diameter and eighteen to twenty-four inches deep, into the soil within the root zone of the tree.

A three inch hole can be drilled by way of a three inch auger that is driven by a half-inch hammer drill (large electric drill). The four inch hole must be drilled with a four inch auger driven by a hand held auger drill (gas powered). I’ve seen both in rental centers.

During the process, “cored” soil usually falls back into the hole drilled, which air easily penetrates.

Generally speaking, holes need to be placed no further than eighteen inches on center, though closer placement will result in additional oxygenation of soil.

Holes should be placed far enough from the base of the tree to eliminate risk of drilling into a “pedestal” root, and extend outward from the tree one foot for each inch of tree diameter. Due to driveways, walks, property lines, and other factors, the area sometimes must be reduced; though aerating a reduced area can still be helpful.

An additional step to improve biological processes within the soil, which benefits roots, is to “vertimulch” during the aeration process.
Vertimulching involves incorporating an organic medium which aids in water retention, aeration, and nutrient holding capacity of the soil. The organic medium is mixed with the native soil within the holes drilled by stirring up with the drill after being placed into the respective hole. Doing so, in a sense, artificially recreates a natural soil environment, to some degree.

There are a host of organic materials that can be used, some designed specifically for the purpose of vertimulching. A rich soil amendment will work well, though an internet search will provide detail of some of the specialized products.

Aeration and vertimulching should only be considered for a tree that is generally in good condition. Neither will “bring back” a tree that is in significant decline.

If in doubt regarding the condition of a tree, consider consulting with a good arborist. Otherwise, open up those “soil nostrils” and help your trees breath.

Brian Arnold, Horticulturist & Certified Arborist, is Manager of Tree, Shrub and Turf Care at Natures Landscape Services, Inc.
His email address is [email protected]