Mulching Craze Gone Wild

By James Donegan

We all want to protect our trees but a human-inspired danger is quickly surpassing the threat of disease and infestation: over-mulching. Within the next decade, over-mulching will be the number one cause of urban tree deterioration if we don’t start to understand how mulching at the base of trees affects their roots and, ultimately, their health.

Tree decline from over-mulching is unfortunately in full force and we are overdue when it comes to educating the public in order to save our trees. The initial purpose of mulching at the base of trees is to hold in moisture at the base of a newly planted tree until the roots are well established. This is necessary during the first two years after planting, after which time mulching should cease, allowing the tree to establish a healthy normal root flare.

Mulching beyond the first two years is “over-mulching” and it can be attributed to the growth of landscaping activity that is focused only about how a yard “looks” instead of the actual health of the trees. When mulch breaks down it turns into composted soil. Tree roots opportunistically grow towards oxygen, water and nutrients, and looser soil, which is what the mulch-turned-compost is.

You may be thinking, “how can fresh compost could be a problem for trees?” but the issue is the newly-composted soil is above the ground inspiring trees roots that should be growing deeper into the ground to instead grow upward toward the surface. This upward root-growth starts girdling around the main root flare of the tree, strangling out the vascular cambium, which, over time, causes trees to deteriorate and eventually die after basically being strangled by it’s own roots.

So instead of mulching around your trees this year, try keeping the area free of mulch and you are likely to see your tree flourish over time.