Common Practices that Harm Trees, Part 2

Trees contribute numerous benefits to a landscape, but the methods for maintenance performed on trees and their surrounding landscape can impact this ability much more than one might think. Before performing work on or around trees, Urban Forestry recommends first doing some research on proper techniques… and practices to avoid. Read below for Part 2 of an article on misguided practices that Urban Forestry frequently observes affecting trees in Edmond (continued from the Winter 2019 issue of Tree Mail).

Rigid Staking

While stakes are not always necessary, newly planted trees can sometimes benefit from extra root ball stabilization while they establish roots in the surrounding soil for anchorage. It’s important to note that we are stabilizing the root ball in this instance, rather than the trunk.

There is a common misconception that stakes are meant to direct a tree’s growth or prevent the trunk from bending. When staking to accomplish these goals, stakes are normally attached tightly, restricting movement in the trunk. This practice prevents development of wood strength, leaving the tree susceptible to breakage. However, when a tree is allowed to sway naturally in the wind, it produces stronger wood that is more likely to adequately support the weight of the canopy over time.
proper staking

Do this instead:

  • Stake only when necessary due to conditions such as top-heavy planting stock, a windy site, or a loose root ball.
  • Attach stakes tightly enough that the tree will not topple out of the planting hole, but loosely enough to allow natural movement of the trunk (see top right picture)
  • Remove stakes no more than one year after they are first applied, or earlier if the tree is sufficiently anchored

Addition of Soil

The drip line, or area beneath the spread of a tree’s canopy, contains a zone known as the “critical root area”. Impact to roots within this area can lead to tree stress and potential decline. When fill soil is brought onto a site and spread across the critical root area of a tree, the added depth can suffocate roots, reducing their access to water and their ability to exchange gases through the soil surface. In addition, soil and the moisture it holds can cause decay in the base of the trunk when it is buried in soil.

We normally see this happening where homeowners create new landscape beds around existing trees by building a planter with stone or edging and filling it with several inches of garden soil (as pictured below). Sometimes this comes in the form of a tree well, an edge cut between the mulched area beneath a tree and surrounding lawn. Soil is removed around the perimeter of the area and then tossed back on top of the critical root area to form a mound.
raised tree well
At the time of planting, people are sometimes inclined to improve the soil in the planting hole by adding a bag of topsoil or compost. This is also a discouraged practice, as the favorable mineral content of the planting hole resulting from the new soil encourages roots to circle in the hole. In the future, this can lead to problems with girdling roots.

Do this instead:

  • When constructing new landscape beds beneath a tree, do not add fill soil. Instead, keep the existing grade and plant directly into existing soil followed by application of a 3-4” thick layer of mulch instead.
  • When digging a tree well, remove excess soil to another location rather than dumping it back on top of the critical root area or trunk. Be careful not to damage roots while digging.
  • When planting new trees, backfill the hole with native soil that originated from the location where the tree is being planted, and refrain from adding compost or topsoil.

Volcano Mulching

Mulch provides many benefits for trees, such as soil moisture retention, regulation of soil temperature, addition of organic matter and soil minerals, and increased growth of absorptive roots. In order to have these impacts, mulch must be applied where the roots are. Thus, the practice of piling mulch in a deep, but small diameter mound against the trunk does not make much sense. This practice, known as volcano mulching, not only has little effectiveness in producing the impacts listed above, but it also results in other potential problems.
Mulch piled up against the trunk can trap moisture against a tree’s bark, increasing susceptibility to decay. The depth can also impair gas exchange between bark and buttress roots that are buried, causing stress.

Do this instead:

  • Apply a 2-4” thick layer of mulch across as much of the area beneath the drip line as possible
  • Pull mulch back off of the trunk by a few inches
Learn more about proper mulching techniques

Overall, these discouraged practices will continue to proliferate for as long as people continue to see them performed by others and assume that they are acceptable methods. Sharing this information with our neighbors and improving practices in our own yards can help to reduce unnecessary tree harm. View Part 1 of Common Practices that Harm Trees.

View other topics from the Summer 2019 issue of Edmond Tree Mail