Homeowners expect so much from shade trees, but those same trees get little care once they get established in the home landscape. Besides getting watered during stressful times, proper mulching can go a long way in the health of the tree.
Mulching trees will control most weeds, conserve soil moisture and lessen the time in the yard trimming after you are done mowing the lawn. In addition, mulch provides root system protection from seasonal changes in temperatures, cold or hot. For a young tree, it also will keep the lawn mower and string trimmer from damaging the trunk, and on our older trees, the mulch ring lessens the handwork needed to maintain the yard. Plus, it can be visually appealing.
There is a right way and wrong way to mulching trees, and we likely see both every day on our neighborhood walks. The correct method does NOT end up looking like the tree is coming out of the top of a volcano. There is not a single sound horticultural reference that will say volcano mulching is a good thing, yet it is quite common.
So, what happens when we mulch the wrong way? Nothing at first. Damage occurs over time, and later when the tree is suffering, we do not relate the volcano mulching to the tree’s symptoms.
The trunk of the tree is designed by nature to be exposed to the elements, and that is why a tree trunk is covered in bark. The bark is a collection of dead cells that provide insulation to the more sensitive parts in the cambium layer just below the surface. When mulch decomposes, it generates heat. This heat damages this important cambium layer, lessening the trees ability to move water and needed nutrients up and down the tree. It also will cause the trunk to begin to decay, allowing pathogens to enter the tree. In addition, because the bark is now in the dark, some trees will even attempt to grow roots out into the mulch rather than into the soil where they belong.
The proper way to mulch is never to allow mulch to cover the bark by leaving a small ring around the trunk exposed down to the soil and mounding up the mulch three or four inches out and away from the tree trunk to the size of the ring appropriate for the size of the tree.
Think about that donut shape and plan on reapplying the mulch as the mulch ring naturally decomposes. This will vary by type of mulch; some break down in a year, others will last two or more. You will know for sure when it is time, as weeds will begin to show up. It is appropriate to freshen the ring by loosening the mulch with a garden rake or tined digger, just don’t leave it rest on the soil to cake over. Valuable moisture can then make its way into the soil profile. After a couple of weeks, the settled much should be about 3 to 4 inches in depth. On last benefit to proper mulching, it actually will save you money as you will not need as much mulch as improper methods.
About the author: Richard Hentschel’s expertise extends across several subject areas with specialties in lawn care, fruit tree production, woody ornamentals, and home and community gardening. During his 45-year career in horticulture and agriculture, Hentschel became a well-known and respected expert for commercial and homeowner audiences, industry organizations, and media. He retired from University of Illinois Extension in April 2022 with nearly 30 years of service as a Horticulture Specialist and Educator in northern Illinois.