There are great benefits to applying mulch to bare areas around your yard and landscape, and I want to bring your attention to one curious mulching practice. You may have noticed mulch piled up around trees in a formation that looks like a science experiment gone wrong, a kind of Vesuvian affliction that those in the horticulture trade call volcano mulching. This is a method where landscape company crews or homeowners apply mulch in a mound up against the bark and directly at the base of a tree, forming a tight cone-shape that can be piled as high as one foot tall and extending up to three feet in diameter. I am uncertain where the seed of this practice began. It may simply be born of tradition, a technique used for its visual appeal and perhaps a notion that the use of mulch in this fashion is healthy for the tree. I learned early in my training that this is an incorrect practice and can contribute to problems associated with tree health. To guide us to use sustainable landscaping techniques, I invite you to take a closer look at the very things we often take for granted: tree bark and mulch function.
Bark biology
The bark that we see covering trunk, branches and twigs of a tree is a collection of dead cells expressed from vascular and cortical tissue that provide protection from insects, disease and extreme temperatures. I like to think of bark as the skin of a tree, and like our skin tree bark needs to be exposed to air to properly function. This is an important point to remember: bark tissue should not be exposed to constant moisture.
The function of mulch
Mulch is often made from organic material such as shredded bark used for covering soil, the practical result being soil moisture retention, soil temperature regulation and weed suppression. As it decays, mulch can help to improve soil structure and add nutrients, and can prevent soil erosion and runoff. Because one property of mulch is to hold moisture, it increases the potential for the bark to decay when piled against bark and becomes a point of entry for fungi, bacteria and insects that can diminish the health of a tree. Also consider that under these conditions, a newly planted tree may begin to grow roots into this mound of mulch and not into the surrounding soil.
No need for volcanoes in your yard
If you are using mulch around your trees, make sure the material is at least 5-inches away from the trunk and no more than 3-inches deep. You can spread the mulch around the tree into the surrounding landscape as wide as you like; tree roots grow an estimated 12 to 14-inches below the soil surface and spread in a radius equal to the tree canopy and beyond. Also keep in mind that you may not need to add mulch annually to specific areas in your landscape. Always evaluate existing mulch depth to determine if more is necessary as a supplement. When applied correctly, mulch can continue to be a benefit to the health of your trees and a beneficial medium for your landscape. I invite you to share your ideas and successes in your garden by browsing online to my Facebook webpage: www.facebook.com/stephenbhorticulturist. Brazoria County AgriLife Extension continues to provide our community with quality programs that enrich lives. I invite you to visit our website to find out about public and professional development programs: https://brazoria.agrilife.org/
