With more than 20 years of experience consulting and practicing arboriculture in the Northwest and Pacific Rim, I’ve seen the same sad story play out again and again.
When trees in the landscape begin to decline, people hire experts like me to try to fix them. The problem? People don’t notice the beautiful landscape trees were planted too deeply. Trees grow upward, and their majesty is what we notice. But to inspect, we need to look down, especially at the area of the root crown.
Hiring experts at that point may delay the inevitable. Trees and woody plants in the landscape often die due to poor cultural practices. One of the worst practices is burying the root flare of a young tree. When a tree of any age has roots that are covered too deeply with soil or mulch, contact with the soil ruins the health and integrity of the low bark.
This is because the low bark on trees is “garden variety” bark. Roots below ground have a different type of coverage, and are resistant to most of the rots that are present. If we wet, heat and crowd garden-variety bark, it is compromised and can be infested or infected. Fungi and insects can make a home, and, eventually, the structure of the tree can suffer as well.
Most of a landscape’s value can be attributed to trees. Studies have been done that determine how much a landscape costs as a measure of real estate value. It is beyond our scope, but we as landscapers can protect these investments with a few simple observations.
Most people do not see past green leaves through to the bones of the landscape where a tree may be declining invisibly. With a little practice, you can increase your observation and detection skills to the point where you can see and solve the most common problems with root flares.
Most of what I see are roots and root flares buried under one or more inches of excess soil. The immediate area of the bark is important, and so is the root crown near the base. The flare is the actual spreading part of the root crown that buttresses the tree and holds roots in place. Pulling away soil is a boost to any tree that is suffering from too much soil.
It’s as simple as looking down. The root crown is defined as the area within a few inches below and above the soil line. The line at the soil level forms a “crown” that is important to respiration, vascular differentiation and structure. Let’s make sure that’s in the proper place.
Most trees are planted too deeply. If it looks like a telephone pole coming out of the ground, it is too deep. Research by Booth and Smiley in 2000 stated, “93% of trees professionally planted are planted too deeply.” Lots of nursery-grown trees are planted too deeply in the pots. This may be a carryover from transplanting or heeling-in.
You can train your eye and hand to make sure soil is pulled back to expose the natural flare. You must look for the spreading or expanding root crown. If it isn’t there, gently pull away soil by hand or with any sort of digging tool — just go easy. Damage in the root crown area is magnified by the presence of soil and fungal spores that take advantage of those openings.
We can also avoid many problems that appear later if we plant in nursery plants at the correct depth. This involves measuring the planting site depth (depth of the hole) and making sure the roots are pointing outward.
When cutting roots, use a clean, sharp tool. I use a special pair of secateurs for underground work. Some root loss is acceptable. I have seen 50% loss of roots improve girdled and bound tree stock. Removing that much rooting material requires staking and extra watering in most cases. The hole we plant in must have soft edges to encourage the roots to keep going. Glazed sides of the site must be broken with a shovel.
Rarely, we find a tree in the landscape that is planted shallowly. It is obvious to the untrained eye; root parts or whole roots are above ground. This shows up immediately, even if it is an erosion problem, and most landscape maintenance workers are trained to add soil in this case. I have seen this help a tree, but remember, do not add too much.
Soil problems quickly become tree problems. Compaction, leaching, poor drainage, and other ills are avoidable, and can be handled right away by cultivating and amending.
In most cases, mixing and amending soils isn’t much of a benefit, so applying a mulch to the cultivated soil, just a couple of inches thick, is best. The mulch will act on the soil and condition it in a short period. This is aided by good cultivation. Commercial mulches with animal waste that have been properly windrowed do the best job as they also add essential nutrients in a time-released manner.
Trees live and die in slow motion to our observation. We must slow our observations to tune in to the signals that trees are putting out to recognize signs of stress. Problems in your treescape will become more visible as you seek the flare.
It’s also important to use proper terms. Soil is not dirt. Soil is a mixture of air, living microorganisms, organic dead stuff and minerals. Air is a combination of gases, such as nitrogen, oxygen and others. The best way to give plants air is to cultivate and offer the soil and growing space needed. Often, roots expand even further from the tree.
We must allow more air, gas exchange, and water absorption to occur deep in the soil. Water moves in all directions in the soil. If the tree does not perk up with cultivation and mulching, a slow small dose of a light fertilizer formulated for trees can be used. Special, low-nitrogen formulations are available for trees. It is easy to overfeed trees while adequately feeding the lawns nearby.
Trees are the longest-living organisms and longest-term survivors. They have outlasted dinosaurs, volcanoes, and hungry mammals over the ages. Now they face string trimmers, chain saws, and the competition of encroaching lawns.
If a tree is planted too deeply, even years after planting, it will be healthier with the careful removal of soil from the root crown.
These new skills are dirt simple. They will also help you as landscape managers to ask the right questions, and educated discussions about tree health and root flare can now be had.
Jack O’Shea is a traveling crew trainer with ACRT Arborist Training. He is an ISA Board Certified Master Arborist, and holds an ISA Tree Risk Assessment Qualification certification. In 2020, Jack graduated from the American Society of Consulting Arborists Consulting Academy. He has been involved in the tree care industry for more than 30 years, and specializes in land use issues and construction mitigation for trees.
For more information, resources and articles, visit www.acrt.com.