JoAnne Skelly: The whys of mulch

JoAnne Skelly

JoAnne Skelly

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Every few years I have certified arborists prune our trees. They always chip anything smaller than what we can use for firewood, generating a mountain of wood chips for me. I use wood chips throughout our landscaped acre, everywhere there isn’t lawn.

I have never purchased chips; all were generated through the years from our own pruned trees. With around 100 trees, a lot of chips can be generated. The wind eventually blows the chips away or they break down over time. I have a new mound of chips from the arborists’ pruning in December and I’m ready to refresh all the beds.

My husband will load the bucket on our tractor and dump loads of chips throughout the landscape. I get the fun job of spreading them all. Why do I care about mulching?

Organic mulch moderates soil temperature extremes, both in summer and winter reducing heat or freeze/thaw damage to roots. Throughout the year it preserves soil moisture by reducing evaporation. It reduces weeds by blocking sunlight to seeds or existing plants. It allows for easier pulling of any weeds that might emerge because their roots can’t get established.

Mulch provides physical protection from lawn mowers or string cutters when it is placed around trees and shrubs in lieu of grass. It can reduce erosion and water runoff, such as under driplines of roofs, or from the splashing of water onto bare soil. It lessens soil compaction.

Over time, the decomposition process of organic mulch releases nutrients, building up a healthier soil and increasing earthworms and other beneficial soil organisms.

It can help decrease some pests such as thrips, leaf miners and even some soil fungal pathogens because it eliminates the splashing of disease organisms from the soil onto plant surfaces. It can moderate the severity of some vegetable diseases. And, last, but not least, it improves aesthetics with a polished look.

There can be disadvantages. Desirable plant seeds can be inhibited without sunlight. If too much mulch is used, you can suffocate plants, especially with “mulch volcanoes” around them. Some pests may increase, such as slugs, cutworms and earwigs.

If too much water is held in the soil by the mulch, plant roots can rot. This isn’t usually a problem in our arid environment, but it was a surprisingly wet winter. Finally, bark and other organic mulches can be flammable unless kept damp.

Apply mulch three inches to four inches deep around plants and in beds. Keep it six inches to twelve inches away from trunks of trees to keep rodents away from the trunks and to prevent trunk rot. For information, visit

JoAnne Skelly is Associate Professor & Extension Educator Emerita at University of Nevada Cooperative Extension. Email


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