March 30, 2022 4 min read
Question: The trees planted in our new subdivision have grass planted right up to the trunks. I want to add mulch around them but don’t know how far out to go or what kind to use.
Answer: Installing mulch is one of the most beneficial things you can do for any tree, but this is especially true for new trees. However, if mulch is too thick or not applied properly, it can kill the tree or other plants.
Most of our trees naturally grow in a forested environment that will have lots of leaf and twig litter slowly decaying on the ground. The tree roots will have an organic blanket that insulates them from the extremes of temperature and slows evaporation. It also cushions them from soil becoming compacted to the point that the roots will not get enough oxygen because the soil’s large pores are smashed shut.
Compare that environment to the typical compacted soil where the tree roots must grow under a lawn that is pulling out the moisture and not supplying much organic matter and you will see that adding mulch will help tree roots.
Adding mulch around the tree will begin to mimic the forest soil environment. Studies have shown that for newly planted trees, an organic bark mulch that extends out wider than the original soil ball or container size helps the tree get a faster start. The tree roots grow into the surrounding soil and the tree gets more water and nutrients so it can support a larger leaf area. More leaves mean more food is produced, which will allow for even more roots. On the other hand, trees that don’t have good root growth after planting tend to take several years to get growing.
Mulch around the base of the tree will prevent the lawn mower or string trimmer from hitting and damaging the tree trunk. These two mechanical devices kill many trees unnecessarily.
Tree roots grow way beyond the tree branches, so if it were a perfect world, the mulch should be applied at least two or three times the width of the tree branches. In many cases, that would mean mulching the whole yard to cover all the tree roots. No lawn at all would be a good thing in many ways but isn’t likely to happen for many people.
Apply a two- to four-inch layer of organic mulch. The type of mulch will vary with the region. Organic mulch can be made from bark, chipped wood, pine needles, cocoa hulls, leaves, compost and other plant materials. The decomposing mulch improves the soil structure and adds nutrients that help plants grow better. Organic mulch breaks down and so it must be replaced.
In fire-prone areas, mulch created from shredded branches created by arborists doing tree trimming is less likely to burn than bark mulch. Bark naturally repels water, so it burns readily. Shredded woody material tends to absorb water, so it doesn’t burn as easily.
Inorganic mulch from gravel, shredded rubber or other material doesn’t have to be replaced as often but does little to help most plants. Gravel mulch in direct sunlight can heat the soil, harming plants.
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March 30, 2022 4 min read