After driving by another row of mulch volcanoes, I decided it was time to spend a little more time talking about proper tree mulching. While mulch is good for trees, piling it against the tree’s trunk is not. The easiest way to describe proper tree mulching is to make mulch rings that look more like doughnuts than volcanoes.
Although this may sound like some personal vendetta, I promise I have both your’s and the trees’ best interests at heart. You spent a lot of money on those trees, right? And those trees will increase your property value if they live to be old, mature trees. You should do everything you can to ensure the trees’ ability to grow up strong and sound.
If you have unknowingly created mulch volcanoes, all is not lost. Just pull the mulch away from the trunk of the tree until you find a root flare. The root flare is the area where the trunk widens just above the first lateral root. You might need a shovel, a trowel, pruners, and/or a knife to cut through roots that have grown up into the mulch. If you find a larger root(s) wrapping around the trunk, you may have a more serious problem, called tree-girdling roots (TGRs).
Tree-girdling roots often emerge when trees are planted too deep, when mulch is piled onto the trunk of the tree, or when trees are left in a growing container for too long. The sad thing is that the roots grow around the trunk in search of oxygen but actually end up choking the tree to death. Sometimes TGRs emerge while the tree is still in the nursery or growing field, but they can be removed at planting. Tree death as a result of TGRs is a long, slow process but a well-recognized one.
In a study in the late 1990s, the University of Maryland found 93 percent of the trees they randomly sampled to be planted or mulched too deep.
Besides TGRs, trees with mulch piled on the base are more susceptible to wood boring insects and root decay fungi. The moisture held against the bark can disrupt the movement of water and nutrients through the tree, thus starving it and making it less able to withstand pest attacks. Suckering shoots are more likely to emerge, and the trees are more susceptible to frost cracks.
Mulch, when applied in a proper doughnut form, is definitely beneficial to trees. It reduces soil temperature and moisture fluctuations and reduces competition with weeds and turf. Think of it as re-creating the forest floor where leaves and plant debris act like mulch over the trees’ root zones.
How deep should the mulch be at the thickest part of the ring? Experts argue and some say it depends on the coarseness of the material, but most universities agree that 2 to 4 inches of mulch provides the most benefit to trees. Just keep the mulch pulled away from the tree’s trunk.
How large should the mulch ring be? Three to 4 feet is the minimum diameter for a tree’s mulch ring if you want to give it the best opportunity at life. More is better in this case — even mature trees will benefit from a ring of mulch.
What should you use? Any organic material works. Wood chips, shredded bark, pine needles and shredded leaves are the most common materials used as tree mulch.
If you do not have any trees, alleviate your mulch volcano stress by telling a friend, neighbor or relative. Barbecue season is coming up, and showing off your knowledge of TGRs always impresses nongardeners. Avoid entering private property and sweeping the mulch away yourself, or touching the plants at a place of business without permission.
Now go out there and protect your tree investment!