One of the most important ways you can take care of the trees in your landscape is to make sure the root flare—also called the root collar or the buttress of the trunk—is exposed to the air. When the flare is underground or covered by mulch or groundcover plants, the bark can remain moist and unable to breath or respire. This invites bacteria, fungal growth and can lead to rot, even death.
When the root flare is not exposed it also encourages girdling roots that can slow down tree growth and cut into the bark. These girdling roots are trying to reach the surface, searching for air. They end up growing right against the root flare, often circling it.
Where is the root flare?
The root flare is located at the base of the trunk where the uppermost roots meet the trunk. This is often called the root crown, root collar, or the buttress of the trunk. If this area is not exposed to the air, the tree becomes predisposed to diseases as well as stressed.
You may notice the trunk widening at the base, this is called the buttress or root flare. However, not all trees show a distinct curve or buttress where they enter the soil. In this case, you can locate the root flare as the place where the topmost root emerges from the trunk.
Problems caused by an unexposed root flare
Roots that grow around the trunk in a circular manner, rather than laterally away from it are called circling roots. When they constrict other roots or trunk growth they are called girdling roots.
Girdling roots will impede the functionality of the girdled trunk or other roots, thereby weakening the tree. Circling roots occasionally occur naturally but are most often associated with nursery practice, improper planting, or unexposed root flare. Luckily, if your tree has produced circling or girdling roots that resulted from unexposed root flare, you or an arborist can safely remove them from the tree.
Fungal and Bacterial Disease
When the root flare of a tree is unexposed to the atmosphere, it can remain moist and highly susceptible to fungal disease such as Phytophthora and Anthracnose, and other tree diseases. The stress that results from the buried root flare will also attract woods boring insects as well as other infections diseases.
Planting too deep Weakens the Tree
Often newly planted trees are planted too deep in the landscape. Trees coming from nurseries are commonly planted too deep in their pots or the burlap is wrapped too high on the trunk. For this reason, many homeowners often plant their trees too deep in the landscape, following the practice of the nursery where they received the plant.
When planting a new tree be sure to plant it high enough so that the root flare is exposed. When digging the hole avoid loosening soil in the bottom of the hole. This will prevent the tree from “sinking” down after it has been planted and watered.
Roots need to Breathe
Roots need to breathe, or respire, and exchange gasses through bark, lenticel, and tiny root hairs. Root respiration, or gas exchange, takes place within a few inches of the soil surface where oxygen from the atmosphere can diffuse down to the roots. If this gas exchange is restricted because the roots are buried too deep, the roots can become injured.
High soil moisture levels resulting from unexposed root flare can also injure or kill roots. The soil remains moist for long periods of time, the oxygen level in the soil is greatly reduced. This impedes root respiration and can kill off some of the root system. With the resulting smaller root systems, less water and nutrients are taken up to support the above ground portion of the tree, resulting in leaf drop and dieback.
The root flare is covered in bark for the most part. If you observe the bark on the trunk you will see that is not covered in soil or mulch. Therefore, the root flare should be kept exposed as well. Wet bark is susceptible to disease and insects and many other problems. When carbon dioxide and oxygen exchange between living bark and the atmosphere is restricted decay may result. Microbes in the damp mulch or soil may decompose the bark along with the organic matter in the mulch or soil. We don’t want that!
The death that results from an unexposed root fare is often blamed on secondary problems such as boring insects, bacteria or fungi. Unexposed root flare is often ignored.
Don’t be a Statistic, Show your Root Flare
If a tree in your landscape has an unexposed root flare, solving the problem can be simple. First, locate the root flare as the place where the first main roots attach to the trunk. Then remove excess soil to expose the root flare as well as the area across the top of the entire root ball. Remove the soil or mulch from the base of the trunk until you can see the uppermost roots. If the tree has developed circling or girdling roots, remove them with pruning shears. If the tree is buried very deep in the soil, consult a tree health specialist. They can use a tool called an air spade to remove soil from around the roots.
After the flare is exposed, a small “ditch” may have been created around the tree. This can be left as is or covered with a light layer of mulch, (cover the soil, not the roots). Don’t worry about standing water in the hold after heavy irrigation or rain. It’s usually not a problem because the water drains away and evaporates fairly quickly. This way the flare will dry out instead of staying saturated from the soil, plants, or mulch that was once burying it.
If you have plants such as English Ivy or a lovely bed of annuals growing right up next to the tree, you should move them away from the base of the tree. These plants hold moisture and collect dust and debris that can build up and smother the root flare. The moisture they hold prevents the trunk from properly breathing.
A little info on tree roots
The importance of healthy roots often goes unnoticed and is occasionally forgotten because they are hidden beneath the ground. Roots are so important to overall tree health! All aboveground parts of a tree depend on roots for anchorage, absorption of water and mineral nutrients, storage of food resources and synthesis of certain organic materials.
Roots systems are actually much closer to the soil surface than most people think. They are rarely deeper than four feet deep in a mature tree. They stay close to the soil surface to take advantage of the moisture and nutrients resulting from organic matter in the uppermost layers of the soil.
Most plants concentrate the majority of their small absorbing roots in the upper 6 inches of soil if the soil surface is protected by mulch or forest litter. If there is no protection the soil surface can become so hot near the surface that roots do not grow in the upper 8 to 10 inches of soil.
Rarely do roots grow down, most plants including trees have their roots in the top three to four feet of the soil. Seedlings, however, tend to have one main taproot or a number of primary roots that form a fibrous root system. As the tree matures, numerous lateral roots, the heart root and xxx replace the original tap root.
Is your root flare showing? The number one culprit for sick trees in an unexposed root flare. If your trees are not looking their best, check to see that no mulch, soil, or plants are covering up the uppermost roots of your tree. This will go a long way to encouraging healthy and vigorous tree.