Archive for Thursday, February 5, 2009

Research buoys use of mulch

February 5, 2009

Today I want to talk about planting trees, but I want to focus on just one aspect of the process. I receive many questions from homeowners about trees, and usually the questions involve the health of a young, newly planted tree. There is much that can go wrong with a newly planted tree, but some of these problems can be prevented. Something as simple as a ring of mulch around a new tree can be the difference between success and failure.

Three researchers from Kansas State University have conducted an experiment to quantify the effect of controlling grass around freshly planted trees. The “subjects” in the study were newly transplanted Eastern redbud and pecan trees.

Five treatments were used to investigate the effects on tree growth due to the encroachment of grass around the tree trunk. The first treatment had trees with bare soil around the trunk. The soil was kept clear of grass with the use of herbicides. The second treatment had a 3 inch-thick layer of mulch around the trees. The remaining three treatments allowed mowed grass to grow unrestricted right up to the trunks. Each of these three treatments used a different species of grass; tall fescue, Bermudagrass, and Kentucky bluegrass.

The trees in all treatments were fertilized according to recommendations and were watered adequately when rainfall was deficient. After two years, the trees were measured to see if there were any differences. The trunks were measured with a caliper 6 inches above the ground. The above-ground portions of the trees were weighed and the leaf area and leaf weight were measured on all trees.

In the bare ground and mulched plots, the trees had trunk diameters twice the size of the trees where tall fescue and Kentucky bluegrass were allowed to grow, and 50 percent larger than the trees that had Bermudagrass growing around them. The Redbuds had a 300 percent weight advantage and the pecans had a 200 percent weight advantage in the plots without grass over those where grass was allowed to grow. Leaf area and leaf weight were also negatively affected in the plots where grass growth around the trunk was allowed.

After looking at these results, the main conclusion drawn is that grass must be controlled around newly planted trees.

Few people want bare soil around a tree, so mulching is the best option to help maintain the health of a new tree. As a rule of thumb, mulch rings with a diameter of three feet and a depth of three inches should be adequate.

If you have questions about this article or need more information, contact me at the Extension Office. Our address is 500 Eisenhower Rd., Suite 103, on the corner of Hughes and Eisenhower roads in Leavenworth, or call (913) 250-2300. I can also be reached by e-mail, at


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