The key to properly mulching a tree? It should look like a bagel, not a volcano

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What does a bagel, a doughnut and mulch around a tree have in common? They are all a circle with a hole in the center. People underestimate the landscape practice of adding too much or not enough mulch around a tree, which leads trees to grow slower or even to die.

We all want our trees to thrive. Research has shown that young trees can double their rate of growth when grass is removed from around the base. Grass competes with water and nutrients, slowing root development.

Strong tree roots produce rapid top growth. Organic wood chips not only remove competition but cool the soil, conserve moisture and release nutrients to improve growth.

A common ailment of young trees is damage to the bark at the tree’s base. We usually create this damage in our zest to remove every blade of grass with the mower or string trimmer.

Young tree bark is tender, thin, and the slightest bump with the mower or trimmer line damages the layer. Once the damage is done, the tree has few defenses to recover. The movement of water and nutrients decreases over time and slows the growth. Rot and decay set in, leading to removal.

Think of a bagel and doughnut as a great example of tree mulching. The tree trunk should be in the middle of the hole. Start by removing the grass out 3 to 6 feet from around the tree.

Next, spread the organic wood mulch over the area to a depth of 2 to 4 inches. Finally, use your fingers to pull the mulch away from the trunk about 3 to 6 inches, creating the doughnut hole. Each year replenish the mulch layer retaining the 2 to 4-inch layer.

Mulching goes off the rails when it looks more like a volcano. Deep mounds of mulch placed around the trunk create this cone-shape mulching. Mulch piled up on the trunk causes the trunk to be constantly damp. This problem leads to rot and decay of the cambium layer.

Once the cambium dies, so does the tree. If the tree does survive, growth slows dramatically, never achieving our goal of a beautiful tree gracing our landscapes.

Healthy tree roots need oxygen for growth. Deep piles of mulch exclude oxygen from the soil. The result is surface root development in the mulch layer, not in the soil where they need to be. These roots are weak and do not provide support for the tree.

If your tree has been improperly mulched, it is easy to correct. Remove the mulch from around the tree. Cut off any surface roots that may have grown into the mulch.

Reapply the mulch around the tree, spreading it out to create the 2 to 4-inch layer and doughnut hole for the trunk. When finished, a properly mulched tree has a slightly raised ring around it, like a thinly sliced bagel, not a volcano.

Want to learn more about good landscaping practices? Then make plans to attend the Johnson County Extension Master Gardener Public Garden Tour, May 21 and 22. More information at johnson.ksu.edu or 913-915-7000. Tickets are also available at area Johnson County garden centers and Hen House markets.

Dennis Patton is a horticulture agent with Kansas State University Research and Extension. Have a question for him or other university extension experts? Email them to garden.help@jocogov.org.



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