Compacted Soil – A Major Problem for Landscape Trees

Compacted soil is the most common major problem for landscape trees. It’s a dirty subject, but researchers have noted that 85 to 90 percent of the problems they see above ground actually originate below ground.

Trees can’t grow well without the proper soil conditions. Soil provides trees and plants with water, nutrients, and anchorage for roots. Soil characteristics are usually given very little consideration when selecting and planting. Soil is not just dirt – but a complex physical, chemical, and biological system. Forest soil contains approximately 50% pore space and 50% organic and inorganic material and feels slightly spongy when you walk on it. Most urban yards have compacted soil and don’t have the same degree of cushioning.

It is common for developers and contractors to compact the soil so that the surface is practically impervious to air and water – often to a bulk density higher than a brick. Compaction decreases total pore space and the resistance to root penetration is increased. The results are slow water infiltration, poor aeration, reduced drainage, increased run-off and erosion, impaired root growth and activity, greater susceptibility to root rots, and reduced biological and mycorrhizal activity. These in turn lead to poor tree growth and appearance, increased insect and disease problems, higher maintenance and shorter life spans for your trees. After diagnosing tree problems for over thirty years, I have found the answer to many of these questions is related to soil compaction.

What can you, as a homeowner, do about tree problems?

• Be aware of your landscape.
• Don’t plant trees that have serious insect or disease problems.
• Match the appropriate tree species to your particular site (trees have certain requirements that must be met in order for them to grow well).
• Avail yourself of educational opportunities at your Extension Office and arboretum.
• Look at websites that give scientific information (www.treesaregood.com is hosted by the International Society of Arboriculture.)
• Hire knowledgeable professionals to assist in both the planting and maintenance of your landscape.

Most homeowners know that trees give us oxygen through photosynthesis, but they are unaware that tree roots use oxygen to perform respiration, the oxidation of organic compounds in the plant cells that release energy for the life processes of the tree. Low levels of oxygen (below 10%) greatly reduce root respiration, limiting root growth and activity. Inadequate soil aeration is one of the most seriously limiting factors in growing plants in the landscape.

The good news is that you can do something about it. There are several processes for aerating the soil. Which method to use depends both upon the site characteristics and your willingness to be a little different from your neighbors. Choices include proper mulching over the root zone, tilling the soil (not an option where plants are already established), vertical mulching, soil fracturing, radial trenching, soil decompaction by Supersonic Air Knife, or a combination of the above.