HOW TO: RID COMPACTION UNDER TREES
Many instances of compaction develop around older trees through pedestrian or vehicular traffic. While the source of compaction may not be very close to the trees, continued use of sidewalks and driveways radiate the effects of compaction to the surrounding area. When the tree has been in place 10 to 30 years and compaction is beginning to take its toll, options for help are limited. One technique that has proven to provide some relief is known as “vertical mulching” or “vertical trenching.” This technique operates under the assumption that increased air penetration into the soil creates a microclimate of oxygen for the roots.
Have utilities marked in the area surrounding the tree(s) to be trenched. To make the process as beneficial as possible, make sure the trencher penetrates fairly deeply, avoiding any power, gas or water lines.
Determine what you will backfill the trench with. There is some debate about the best material, but one study shows that using pulverized backfill vs. sand vs. highly organic topsoil can produce the same results because all create more air spaces than were present before.
The trenches should begin 10 feet away from the trunk and radiate out from the trunk. There is no set recipe for length or depth of the trench. Some projects call for trenches to be dug 10-feet long × 2-feet deep × 4-inches wide; others call for trenches anywhere from 4 to 24 inches wide and 12 to 18 inches deep.
Work slowly to avoid cutting roots larger than 1 inch in diameter.
Backfill the trenches with the material of your choice, then mulch and water around the area. As with all tree fertilization, there is some disagreement on whether to fertilize or not. If you chose to fertilize, use a balanced fertilizer.
The process does not remove large quantities of soil compared to the root zone itself. For instance, the area under a tree that is 20-feet wide, 20-feet long and 2-feet deep would have a soil volume equal to 800 cubic feet. Trenching 10-feet long by 4-inches wide by 2-feet deep would remove/loosen/treat 6.7 cubic feet of soil. If you dug five trenches around the tree, the volume would equal 33 cubic feet or 4 percent of the total volume. Could this save the tree? Chances are that the increased, localized oxygen and optimum microenvironment for root development may be the boost your compaction-damaged tree needs to survive.
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