I would hate it if someone made me wear a turtleneck sweater (remember that 70s fad, boomer friends?) all summer long. Well, it appears that many people in our region do that to our young trees with improper mulching. Piling or mounding mulch up against a tree trunk holds heat and moisture where it shouldn’t, but the practice seems ubiquitous by area homeowners and landscape workers alike. It’s time to “free the flare,” the root flare that is.

If the lines of a tree trunk are parallel as they disappear at the soil or mulch level, the tree is either planted too deeply or mulched too high. There should always be a visible root flare, where the stem widens as it becomes the root structure. This part of the tree needs to be exposed to air, not smothered. Think of the turtleneck versus an open collar shirt – let the base of your neck where it transitions to your shoulders be free to breathe.

It is true that proper mulch reduces soil moisture loss through evaporation, important in times of drought. Good mulch can also control weed germination and growth, and insulate the soil protecting roots from extreme summer and winter temperatures. A quality organic mulch can improve soil biology, aeration, structure (soil aggregates), and drainage over time. Mulch is fine in the root zone of the tree, but never up to or touching the trunk.

A good donut-like ring of mulch kept several inches away from the young tree trunk can reduce the likelihood of tree damage from string trimmers and lawn mowers. It can also give plant beds that uniform, cared-for look we humans crave. Trees growing in a natural forest environment have their roots anchored in a rich, well aerated soil full of essential nutrients and soil microorganisms. The soil is blanketed by fallen leaves and other organic materials that organisms break down to release nutrients into the soil. This environment is optimal for root growth and mineral uptake. Urban landscapes and new developments are typically harsher environments with poor-quality soil, reduced organic matter, and large fluctuations in soil temperature and moisture. Many benefits of the natural environment can be replicated, while maintaining a more formal appearance, with the proper application of a mulch. 

There are several types of organic mulch that can be used around trees. Wood chips, pine needles, softwood bark and leaves are readily available. My preference is for pine needles; they remain “breathable” rather than compacted, and seem to knit together to stay in place with heavy rains. Pine bark tends to become like little boats that travel quickly into our storm drains, adding unwanted nutrient to our nearby waterbodies. 

Different mulch types decompose at different rates depending on the material, climate, and presence of soil microorganisms, but decomposition is a good thing as it contributes to the organic matter content of the soil. Sandy soils in our region typically have about 1% organic matter; 5% would be a good target for the healthiest soils and plants. For this reason, I don’t recommend an inorganic mulch such as rocks, stones or shredded tires. Let’s build our soils instead!

Too much mulch is harmful; limit the mulching depth to 2 or 3 inches in the root zone, but again, never touching the trunk. If the mulch is mounded up around the trunk – a mulch volcano - it is likely killing the tree and needs to be pulled away to let the tree breathe and thrive. So, let’s work together to “free the flare” of our area trees.

Lloyd Singleton is the director of the N.C. Cooperative Extension - New Hanover County Center and Arboretum. He can be reached at lsingleton@nhcgov.com or 910-798-7660. The Arboretum grounds, located at 6206 Oleander Drive in Wilmington, are free to visit and open daily from 8 a.m.–5 p.m.