Menu Close

Trees and Mulch

Mulch against the trunk of a tree causes many long term problems.
Always pull mulch away from the trunk of a tree. The root flare should always be visible.
An Air Spade or Air Knife is the tool of choice to loosen fill soil and move it away from the trunk.

Mulch is great for on your soil, not against your tree trunk.

Nature has a wonderful way of replenishing nutrients that are lost from soils due to rain, erosion, oxidation, or the most common method – human interference. The way nature replenishes its lost nutrients, and rebuilds its damaged soil structure is by adding organic matter. The two most beneficial forms of soil organic matter (SOM) are mulch and roots. When leaves fall, when branches break, when bugs die, they incorporated into the forest floor and release their organic constituents back into the soil. All the nitrogen, sugars, starches, carbon, magnesium, phosphorus, potassium, iron, boron, etc. is released and cycled back into the soil. If the SOM is recalcitrant (not readily available), then soil microorganisms such as bacteria and fungi begin to work their enzymatic magic and break down organic products into readily available components that are ready for uptake by plants. As roots from trees, grasses, or any other plant begin to wind their way through soils, a portion of their biomass will die and that too will become a rich source of SOM.

Mulch is a wonderful addition to soil. It will create a home for microorganisms that will break down the mulch, create a rich top soil that will invite root growth, make all your plants healthier, and more often than not, it’s free! Lawn clippings, raked up leaves, ground up tree parts, compost, and many other forms of potential soil organic matter exist that are frequently thrown away. This includes oak leaves that many people bag and place on the curb to be hauled away to the landfill.

Mulch is also one of our most useful tools for improving soils that have been damaged by compaction or soils that have had the important high-organic topsoil profile removed during development. During the last phase of construction, new trees are often planted in these hard soils that have been depleted of organic matter and somehow expected to thrive.

Mulch can help but keep it away from the tree trunk. Moisture from mulch can cause trunk rot. Mulch applied too high and against the tree trunk will stimulate small roots to grow around your tree. Years later, these roots can strangle and kill the tree (see image 3). 

Stay away from cedar and cypress mulch. These products do not prevent pests, or provide any other benefit often touted by companies selling these products at a premium. They will however cause the unnecessary culling of non-sustainable cedar and cypress trees. Dyed wood chips are good for only one thing – adhering to HOA landscaping rules. Dyed mulch does not provide ecological benefits, but some folks insist that it looks pretty.

Stay away from “deep root” injections, “deep soil” feeding, trunk injections, fertilizer stakes, or any other trendy method of adding product to the soil. If it sounds like snake oil, that’s because it is. All of these methods are largely ineffective, expensive, and do not enhance your soil. SOM (soil organic matter) is mulch, plain and simple. Leaves, branches, bark, heartwood, acorns, are all forms of mulch. Take your pick, place it on top of your soil no deeper than 4 inches after settling, carefully mix it in to your topsoil being careful not to damage tree roots, and add water. It’s that simple. It’s the way Mother Nature has been doing it for a very, very long time.

(Reprinted from Native Plant Consulting newsletter, January, 2018)

Danny Lippi
ISA* Board Certified Master Arborist FL-6145B