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Vertical Mulching of Trees “Giving Tree Roots a Breath of Air”
Written by Mark A. Webber
Board Certified Master Arborist #OH-0824B
Trees in the urban landscape today struggle at best at becoming the large plants that, we want them to become. This is related to a wide range of factors. One of the major limiting factors is lack of adequate soil volume for a tree to grow. The general rule of thumb is trees require 1-2 cubic yards of well oxygenated soil for every cubic yard of tree canopy. The vast majority of urban soils in homes built post 1960, don’t provide the adequate soil volume due to the fact the urban soils are stripped and compacted to at least 90% proctor. The value of 90% simple means that the soil only has 10% oxygen content and most plants require 21% soil oxygen content to thrive.
The process of Vertical Mulching is one of the most powerful ways that the tree owner can increase oxygen content in the soil, which directly increases adequate soil volume for the tree to grow roots and the tree will become larger and healthier plants.
What is Vertical Mulching?
Vertical mulching is the process of making many holes in the soil of the root zone of a particular tree with the purpose of creating many entryways for air, moisture, and nutrients to reach the roots of a given tree. This process improves the overall health and vigor of any tree. To properly vertical mulch, you will need an electric or gasoline powered drill and a 2” to 3” diameter auger. This equipment is available from any tool rental.
Starting at 8-10 ft. away from the trunk (no feeder roots there) drill holes on 2 ft. centers 15-18” deep in all directions. Leave the soil that is removed from the hole on the ground near the hole and it will blend back into the soil. This circular pattern should extend at least 30% beyond the drip line of the tree.
(Photo Courtesy of Texas A. &M.)
The process of drilling holes under trees and shrubs and then filling those holes with a coarse soil amendment has been done with favorable results with many plants suffering from low oxygen volume soils. Those mediums can include compost/peat moss and other biodegraded materials.
To Fertilize or Not
Research indicates that improper fertilization can cause harm to trees and it is a “Best Practice” to always perform a soil and or a foliar analysis to any tree prior to fertilizer applications. You can reach your local extension service for al list soil testing labs in your area.
Word of Caution
Be careful where you drill, if you have an underground sprinkler system, landscape lighting, any utilities, stones, tree roots and other un foreseen obstacles extreme caution should be observed and taken. In Ohio, you are required to call the Ohio utilities protection services (1-800-362-2764) or 811 on your cell phone to mark any other underground systems before you dig holes. There is no charge for this service.
Additionally some site condition may be difficult to use single person hand held self-propelled augers due to rocks beneath the soil, so it may be prudent to use a 2 person units in such situations. Be sure to always wear eye, hearing, face, proper foot wear other recommended personal protection equipment (PPE) and or safety wear when doing soil drilling.
Helping Trees Grow!
Vertical Mulching allows the homeowner/landscapers/arborists to correct soil conditions that may be inhibiting desired plant growth without replacing the plant and/or the soil. Many times as the tree grows this process may be replicated but on a larger scale to compensate for the trees ever expanding canopy.
For more ways to grow better trees visit www.treesaregood.org ;