Mulch excellent for landscape when used properly

Allen D. Owings, Young, John, Gill, Daniel J.  |  9/15/2008 6:13:11 PM

Sustainable Landscapes -- News You Can Use Distributed 09/15/08

By LSU AgCenter Horticulturists

If you don’t include mulches in your gardening efforts, you really should give them a try. You will be amazed by how much they spare you from weeding and how nice they can make your yard and garden look.

What exactly is mulch? Mulch is a material spread over the ground to cover bare soil to provide a variety of benefits to plants.

Organic mulches are an important part of sustainable landscaping. They recycle yard waste, lessen the need for fertilizers, reduce the need for irrigation and minimize the use of herbicides.

Organic mulches are derived from once-living materials. As they decompose, they return valuable and beneficial organic matter to the soil. They decay over time and must be replenished once or twice a year, depending on the type of mulch used. Spring and fall are good times to replenish mulch.

The first and foremost reason to use mulches is weed control. Mulches reduce weed seed germination and subsequent growth. They do this by blocking light to seeds requiring light for germination. To act as a weed barrier, mulches must be applied in a thick layer.

All ornamental plants benefit from mulch when it is applied correctly. Mulches have numerous benefits for plants, soil and the surrounding area. They:

– Conserve soil moisture and reduce the need for frequent irrigation. By slowing down evaporation from the soil surface, mulches keep the soil from drying out too quickly.

– Prevent crusting and compaction of the soil surface. If you mulch as soon as you finish planting, the mulch will help keep the soil pliable and reduce erosion. Remember, a loose soil is easier for roots to grow through and absorb water faster.

– Maintain a steady soil temperature. Organic mulches help insulate the soil and moderate soil temperatures – keeping the soil warmer in winter and cooler in summer – to help roots from stressful temperature changes.

– Add beauty to the landscape. Many people apply mulches to their landscape simply because they feel it makes their yard more attractive. Mulches come in a variety of colors, but remember to apply mulches correctly to reap their rewards other than just good looks.

One of the best mulches is yard wastes. It is free and filled with nutrients. Ideally, grass clippings returned to the yard and dried leaves raked from under trees are excellent mulches. There is no best mulch for every situation. Factors to consider include personal preference, availability, cost and durability.

We LSU AgCenter horticulturists recommend mulching annual bedding plants and herbaceous perennials to a depth of 1 inch, shrubs to a depth of 2 inches and trees to a depth of 3-4 inches.

It is important to “go out” with mulch instead of “going up” with it. In other words, spread out mulch horizontally instead of piling it up vertically. Typical mulches include pine straw and pine bark. At the LaHouse Home and Landscape Resource Center, where our demonstration landscaping is, we are using synthetic pine straw, eucalyptus mulch and dyed wood chips.

Excessive mulching around trees and shrubs, however, causes problems. One of the tendencies in landscapes is to add piles of mulch (sometimes resembling the shape of a volcano or fire ant mound) around bases of trees, especially small-flowering trees, such as crape myrtles. Problems include phloem tissue death (caused by reduced oxygen exchange) and increased fungal and bacterial infections (from increased moisture around the trunk). A too-deep layer of decomposing mulch also builds up heat that kills stem and trunk tissue. In addition, too much mulch is a habitat for rodents that feed on plant tissue.

LSU AgCenter scientists are conducting mulch research and demonstration projects. Studies examine mulching depths, color retention, the effect of mulch type on weed suppression and other issues.

Come to LaHouse to see sustainable landscape practices in action. LaHouse is located near the intersection of Burbank Drive and Nicholson Drive (La. Hwy 30) in Baton Rouge across the street from the new LSU baseball stadium and next to the LSU Golf Course parking lot. Go to and for more information.


Dan Gill at (225) 578-2222 or
Allen D. Owings at (985) 543-4125 or
John Young at (225) 578-2415 or 578-2222 or
Editor: Mark Claesgens at (225) 578-2939 or

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