Q: Will aeration hurt the roots of my trees?
-Penny, Wheat Ridge
A: To understand how aeration benefits trees, it is important to understand a little bit of tree physiology.
As most people know, leaves absorb carbon dioxide and release oxygen. This process provides atmospheric oxygen and helps to sustain all kinds of life. Conversely, roots absorb oxygen and release carbon dioxide. Roots must grow close to the surface where oxygen diffuses into the soil at high enough concentrations for them to survive. The absorbing roots (about 80 percent to 90 percent of the root system) are the most oxygen-dependent roots and usually grow in about the top 10 inches of soil.
The depth depends on the type of soil type. For example, roots will grow deeper in sand and shallower in heavy clay. Sinker or anchor roots, which are relatively few in number, grow deep into the soil where oxygen levels are significantly lower. These roots are able to obtain oxygen from the tree.
Aeration provides increased diffusion of oxygen into the soil and is beneficial to plant life, especially in the heavy clay soils of many parts of Colorado. Aeration also recycles organic matter, which is another benefit to plant life. In the recycling process, the cores or plugs produced by aeration break down on the top of the turf. These plugs add essential organic matter to the landscape as they are reincorporated into the clay and sand soils of Colorado.
The depth, uniformity, and amount of cores or plugs are important factors in aeration. Drum-style aerators are the most common, but they do not produce as deep, as many, or as uniform of cores as a cam-driven aerator. Drum-style aerators roll over the turf using the weight of the machine to drive the tines into the soil.
Cam-driven aerators, on the other hand, drive the tines into the soil like the camshaft in an engine. Cam-driven aerators also produce more cores per square foot.
Most aerations are performed to increase the overall health of the lawn. Trees and shrubs also benefit from aeration applications if the proper equipment is used. Cam-driven aerators are significantly more expensive than drum-style aerators, so the application price will be higher. But as in most cases, you get what you pay for.
Care should be taken not to aerate too close to trees to avoid damaging the buttress roots. Some trees, such as Norway maple, cottonwood, and spruce, have shallow root systems, and the aerator can damage roots by punching holes in them. This damage can lead to decay, which could affect the tree’s stability.
Robert Brudenell is a registered consulting arborist and owner of The Natural Way Inc. Send questions to Robert@thenaturalwayinc.net.
