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So you think you can mulch

  • 9/28/2016 3:34:00 PM
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Avoid the volcano approach when mulching your tree - more tips for healthy trees | Iowa DNRThis article originally appeared in the September/October 2016 issue of Iowa Outdoors magazine
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Mulching can be the best thing you can do to promote the health of trees, shrubs and plants. It can also be the worst, if done improperly. 

Trees growing in a natural forest environment enjoy the benefits of nature’s mulch—leaves, twigs, organic material and other organisms that replenish and recycle nutrients. They are often anchored in rich, aerated soil. In urban landscapes, compacted soil of poor quality, reduced organic matter and fluctuating soil temperatures and moisture content plague new plantings. 

Done right, mulching can reduce moisture loss from evaporation and control weed germination and growth. It insulates soil to protect roots from extreme seasonal temperatures. Mulch improves soil biology, structure and fertility, inhibits plant diseases and reduces the likelihood of damage from mowers and weed trimmers. 

Improper mulching, like applying it too thick or building a “volcano” around the trunk, can lead to excess soil moisture in the root zone, which can stress the plant and cause root rot. Conversely, once matted, they can prevent moisture penetration. Piling mulch against the tree trunk can direct water away from the root system. Moisture stored in the pile can penetrate the bark and suffocate phloem cells, potentially killing the tree. It can also attract rodents that chew the bark, as well as insect and disease issues. 

While there are many types of mulch material available, tree experts say organic mulches, like natural wood chips, pine needles, bark, cocoa hulls and leaves are best because they are natural and derived from plants. Avoid inorganic mulches that don’t break down. They add nothing to soil quality. Also avoid cypress mulch, as these ecosystems are being destroyed for production. 

Pull grass or weeds from around the trunk. Identify the dripline, located directly under the outer circumference of the tree branches, essentially where rain would drip from. That is where the tiny rootlets are located that take up water for the tree. For well-drained soils, apply a 2- to 4-inch layer of mulch at least as wide as the tree’s drip line. Pull back mulch several inches from the trunk. The mulch ring should look like a donut, not a volcano. Count on 3 to 4 cubic feet of wood mulch per tree. If adding to existing mulch, rake or break up any matted material. Add mulch each year to maintain the 2- to 4-inch depth and widen the ring as the dripline extends. While adding mulch every year might take a little added time, the decomposition process improves soil quality. 

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