Mulches can help trees and plants stay cool

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Conserving soil moisture is essential during Nevada's hot, dry and breezy summers, and one of the best ways of accomplishing this in your landscape is through mulching, says University of Nevada Cooperative Extension Educator JoAnne Skelly.

Skelly, an expert in natural resource management and urban horticulture, said mulch is any material used to cover the soil surface. Organic mulches usually come from plant materials and can be things such as pine needles, straw, bark nuggets or grass clippings. Compost can be a mulch too.

Skelly, the Extension Educator for Carson City and Storey County, noted that plants stay cool in the summer by pulling water out of the soil and sending it out through pores in their leaves. The moisture then evaporates off the leaves and lowers leaf temperatures.

"But this can be a big job," Skelly said. "Think about a tall tree sucking up water from the ground to its tallest point and to each and every leaf. It's amazing that plants can do this, but only if the water is available in the soil."

Organic mulch not only conserves soil moisture for plants, but it also keeps soils cooler, which can decrease a plant's water requirements.

Skelly noted that one problem with many mulches is that they can burn, and some burn faster and spread more readily than others. A study by Cooperative Extension nature resource specialist Ed Smith of eight mulches commonly used in Nevada found that composted wood chips demonstrated the least hazardous fire behavior, and Skelly recommended that homeowners maintain a noncombustible ignition-resistant zone within five feet of their homes and other structures.

"To keep ignition potential low, place mulches around plants out to their dripline - the furthest reach of their branches," Skelly said. "Do not use them in a widespread or continuous manner throughout the landscape. This will conserve soil moisture around individual plants while reducing the potential for fire spread."

Skelly said it's also important to keep mulched areas moist.

"Drip irrigation often does not wet an entire area unless microsprayers are used, so dry mulch areas can exist even under irrigation," Skelly said.

She added that another way of conserving soil moisture for a specific plant, such as a tree, is to remove the lawn around the plant to the dripline and put mulch there instead. The tree or shrub will not have to compete with the lawn for available water.


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