Good Mulch, Bad Mulch. Is There Really A Difference?

August 29, 2011
in Category: All About Trees, OTC Helpful Hints
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Fall Is a Great Time to Mulch

“I know we’re supposed to do something to our trees in the fall, but what?” Tree owners often feel compelled to spray, prune or apply something to their trees and landscape plants on a regular basis. But, unless there is a specific reason to spray, prune or apply things to landscape trees, the best thing to “do” to keep your trees healthy would be to apply a layer of mulch.

“Fall is a great time to be out in the yard spreading shovels-full of composted woodchip mulch under your trees,” says Tchukki Andersen, staff arborist with the Tree Care Industry Association. “Trees with mulched root zones are usually larger, more vigorous, develop faster and have higher rates of survival than plants surrounded by turf grass or bare dirt. Mulches retain soil moisture and reduce erosion and soil compaction.”

Mulched trees also have fewer weeds, which reduces the need for the roots to compete for limited resources. The soil under the mulch also likely stays warmer longer into the winter and also warms faster in the spring, helping extend the growing season for plants.

Organic mulches are a favorite among professional arborists, who view wood chips as an excellent, attractive mulch for trees. Other organic mulches include bark chips, ground bark, composted lawn clippings, leaves and straw. These mulches are high in cellulose and low in nitrogen, and should be free of weed seeds.

Good Mulching

How Wide is Wide? A good mulch bed should extend out at least three feet from a tree’s trunk in all directions, though extending out to the dripline is preferred. The fine, absorbing tree roots extend

out into the soil, and mulch provides many health-related benefits for those roots. Keep organic mulches several inches away from the base of the tree to avoid rot and diseases.

How Deep is Deep? The mulch bed depth should be maintained at 2 to 4 inches.

Go Ahead, Cover the Grass! If there is grass in the area that needs to be mulched, put a five-page layer of newspaper over the grass, get it wet, then add mulch on top (this will help keep the grass from growing up through the mulch).

Use the Right Mulch. For poor soils, use well-composted mulch to build up the nutrients. Soils that are healthy will do fine with a highly stable softwood bark (such as cypress bark), which doesn’t break down as easily.

Bad Mulching

No Volcanoes, Please! The biggest no-no when mulching is to create a “mulch volcano” that is piled high around the base of the tree. This practice traps moisture around the tree trunk and root flare leading to decay and, eventually, structural failure.

Avoid Fine Mulch. Thick blankets of fine mulch can become matted and prevent the penetration of water and air.

Don’t Let Mulch Sour. Low oxygen levels (from packed-down mulch) creates a toxic “sour” mulch – which may give off pungent odors, and even worse, the compounds produced (methanol and acetic acid) can kill young plants.

Don’t Keep Adding New Mulch on Top of the Old. While mulch does decompose, you do not want to accumulate excessive mulch year after year by adding fresh mulch every spring. If you want the look of fresh mulch, break up the old with a rake, and only add a layer of new on top if there is less than 4 inches in depth.

Find a Professional

A professional arborist can assess your landscape and work with you to determine whether your trees and shrubs would benefit from pruning. Oregon Tree Care is a proud member of the TCIA.

This article is reprinted with membership permission from the Tree Care Industry Association (TCIA).

 

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