Dobe on a branch


Soil Level For Trees

This is a subject of much interest to me because the trees are suffering. When the soil around a tree gets too high, problems develop. This can occur naturally but is more often caused by people. People who love their trees are hurting and even killing their trees for lack of knowledge. The problem is worsened by the presence of a conflict of interest that exists among the industries. Cross-discipline communications is going on but there is need for improvement. Hopefully, this article will help. Another complication that makes the issue and the writing of an article on the subject difficult is the close association between mulch and soil levels.

Soil is one thing, mulch is another. The difficulty is that both cause problems for trees when applied incorrectly and mulch, good organic mulch that is, becomes soil eventually. Here I want to write about soil level as it relates to tree health and find that I have to write about mulch at the same time. My hope is that I can write another article about mulch later, but that might be a while so I will include some information here. Bear with me, please, as I try to sort this out in a way that will work, and get back to the conflict of interest that is hurting the trees in the way it relates to soil level.

Landscapers and builders/developers (sometimes the same but sometimes different companies or different people) cause damage to trees in the normal course of their respective business. Builders prepare the land for building structures and landscapers make the prepared land beautiful. After scraping the earth with heavy equipment the landscapers, and sometimes the builder/developer bring in soil to cover the land for various reasons. The soil level gets raised. Next, sod or turf (grass grown somewhere then cut into rectangular sheets to be transplanted) gets put down and the soil level gets raised again. Irrigation systems often get installed to maintain the sod. By the time all this is done, any pre-existing trees that were preserved have to cope with an unhealthy high soil level that actually comes as a mix of detriment and benefit. High soil levels hurt, but new rich soil helps.

Sometimes homeowners feel it is a good idea to make rings around the trunks of trees by removing the grass and then covering the bare soil with mulch. Sometimes the soil around the trunk will be cultivated, augmented and raised. Then flowers will be planted there. This practices is not good for the trees, but it can even be worse.

I was called out to work on the trees at a man's house. My initial inspection revealed a cluster of many live oak trees that had over two feet deep flower beds built around them. The beds were contained by expensive rock walls over two feet high that were mounted on footers dug into the ground. These fine raised beds were well done and beautiful, and worse yet, they were brand new. I am afraid my advice to the homeowner made someone angry. I got a nasty anonymous message a couple days later. The homeowner had spent a lot of money to make his property more beautiful. The landscaper was probably happy to get the job. I made sure the owner of the trees knew that the trees inside this new raised bed would die because of the trunks of the trees were underground. The dirt was so high on the trunks of the trees that they would not have survived long. My job is taking care of trees, even when someone else doesn't like me for doing it.

Soil Level and Mulch

Using mulch around tree trunks is a practice that is far too common. I am not sure how this practice got started. My guess is that it comes from the practice seen when trees are transplanted, and even that is often done wrong. In any case, it is not a good idea to put mulch around the trunks of trees, and that includes transplanted trees. There are several factors involved, and I will address these factors in the following text. For now, I want to work on getting this practice discontinued. Spread the word! I am constantly having to deal with this issue when I am out in the field. Everywhere I go I see mulch rings around the trunks of trees. When I see this it makes me wonder why the property owner is trying to torture the trees to death. Of course, the answer is obvious. The people know not what they do.

A tree that is established, (the roots are in the native soil), does not have the ability to absorb nutrients and moisture in the area right around the trunk. The roots that feed and drink are further out, under the limbs. The area near the trunk needs to be kept dry and clean because that is the area of the root system and trunk that is constantly under attack by various organisms and is an area that supports tremendous amounts of weight and stress. Anything that weakens the tree in that area must be avoided, and that includes mulch, flower beds,rocks,weed barriers and almost everything else.

If you gently dig away a small area of soil from next to a tree trunk you will see many forms of life. These life forms are finding shelter and sustenance there. Many of these life forms would love to get access to the tree's internal systems and they are ever vigilant for an opportunity to do just that. Moisture aids their cause. Mulch, therefore, aids their cause. Decay is promoted by moisture caused by mulch. It just is not a good idea to put a mulch ring around the trunk of a tree.

The best thing to do for the tree is the make a bare dirt circle around the trunk and keep it clean and dry. You can see this done all around the city. Many people know what to do. If the soil is covering the bark of the tree, remove it. If you find little roots growing in the area, remove them. I suggest you call me, or another arborist, before cutting roots. Usually, a large tree will not have small roots near the trunk and it is safe to remove them, but be careful. Make sure you know what you are doing. Consult a certified arborist before doing anything to your trees. You can call me and get all the help you want, with limits. I am but one person.

The mulch issue is complicated by a practice that is very common. Trees get planted in a container of some sort, like a plastic flower pot, are allowed to grow too long in the container, and then are planted in the earth. I have yet to see a container grown tree that did not have the growth pattern of the roots deformed. They are forced to grow in a circle the shape of the container. Need I say this is not good for the tree? Evidently I do. If you consider the distance from the trunk the roots of a tree grow, it becomes evident right away that even a tree with a one inch diameter trunk would have to have a container so large as to make the practice impractical. Some of the larger container grown trees that get bought and planted would require a container that could not be carried on legal sized trucks if it had enough room to grow a natural root zone. I plan to write more about this in another part of this web site, but for now I need to make it clear that the container grown trees that are transplanted into the earth have an abnormal roots system clustered very near the trunks of the trees that do feed and drink in the area close to the trunk and require mulch in most cases. This is one of the conflicts of interest I mentioned earlier. So, when you are trying to get a container grown tree to survive be sure to use mulch wisely and, even in this situation, keep the mulch away from the trunks of the "young hopefuls," as John Muir would say.

Trees in Central Texas have adapted to the weather that was the average weather of the past millions of years. That means they do not like lots of moisture. Austin, is (or I should say "was") in the northern most border of the northern sub-tropical zone of the continent. This sounds like we get rain that is a little tropical. The fact is that our average rainfall has been about 32 inches per year for a long, long time. The critical factor, though, is that the rains came mostly in huge downpours a few times a year. That, coupled with the sparse soil and awesome drainage, has meant low moisture for trees and low moisture near the trunks of trees. It also has caused the trees to be very drought tolerant. Six months without a drop of rain in the Austin area causes very little tree death. On the other hand, rain every day would eventually destroy most of the native vegetation around here, including trees. So, why the rush to mulch trees in yards, even yards with built-in irrigation systems (sprinklers for lawns)?

I have removed many very old dead cedar (Ash Juniper) trees from landscaped and irrigated lawns. One man had expensive consultants from A&M come to save a dying cedar tree. They offered no suggestions. According to the owner, after much testing and examination, the scientist told him the tree was just in decline, suggesting natural causes. Perhaps they did not see the sprinkler head near the trunk that was keeping the beautiful grass alive. This grass came in the form of sod that was laid on top of a clay containing base installed during construction. Sod has a rich layer of soil with it. The poor old cedar tree that the homeowner loved was killed by too much moisture and possibly by too much nitrogen. He didn't discover The Tree Tender until he searched for a tree service to remove a dead tree. I saved the huge cedar trunk of that tree. I still have it and hope to make something from it.It is a beautiful column of cedar wood over two feet wide at the base, nearly two feet wide at the top, and about fifteen feet long. Imagine the beauty and glory of that ancient tree living long enough to get that big only to be destroyed when people moved in around it. The tree might have survived the watering had it not been for the extra soil and sod acting as a moisture retainer (mulch). What I want to do now is to continue with this subject, especially as it relates to soil level.

Mulch causes more problems than those derived from excess moisture. Of critical importance to the trees in the Austin area is the fact that the mulch almost always raises the soil level at the base of the trunk. The live oaks of Central Texas do not respond favorably to this condition. I have to cope with the trouble caused by elevated soil levels far too often. It is a daily occurrence. The problem is compound and difficult to explain in written text. I will make the effort.

First, we need to understand that trees come with their soil level built into the DNA, it is a genetically pre-determined soil level. Deviations in the level of the soil near a tree trunk have various effects on any given species and the effects vary within the species. Our live oaks can tolerate lowered soil levels, but they cannot long (and I mean "long" in tree time) tolerate raised soil levels. None of the other trees in our area can tolerate the elevated soil level, but they respond differently. The pictures below are examples of how live oaks respond to raised soil level. I took the pictures myself. It is an Austin live oak. Some live oaks do not develop these symptoms. Mine did not. I do not know why some do while others do not. If your tree shows these symptoms, you can be sure that the soil that is over the proper soil level is being populated with new rootss that are increasing in number, diameter, and length constantly. They become like a plate of spaghetti all tangled together. However, these roots grow. The become pressed against each other and eventually weld themselves together to become a "tumerous, woody, mass" that keeps growing and begins to grow roots from the bottom of the mass and into the soil below, more or less straight down; sinker roots. This often chokes the bigger and better roots and causes more harm to the part of the tree we enjoy, the canopy. If the main root system of the tree dies, the crown will die. With the new (adventitious) roots and leaf sprouts, the tree will not actually die altogether, just the main canopy will die. It is a survival technique, but one better avoided.


These pictures show the base of a large live oak surrounded by young live oak leaves. The leaves have small thorns along the edges (margins) something like those found on holly leaves. This is a form of protection for young live oak leaves. These leaves are growing on stems that grew from new roots that grew from the soil covered area of the trunk of the tree when the bark got covered by soil.It is the trees effort to protect itself and to take advantage of the new soil. This process essentially saves the life of the tree considering the fact that the large part of the tree (what we consider the tree itself) could eventually die leaving only the little sprouts, which might not be so little by the time they become the last remaining vestige of the tree as we knew it before the soil level was raised.

I have drawn some pictures to help you understand the problem. I hope they will help explain the problem as it exists with live oaks. You need to understand that even though this reaction to elevated soil levels is typical of live oaks, soil level is also vital to all trees. Keep in mind that the soil level is a genetically determined place on the tree. It is where bark meets root covering. These are two different substances and each has its own ability to stay healthy and to tolerate various conditions. Bark is designed to protect the tree from the atmosphere and all its variables, i.e. light, water, insects, fungi, and more. Bark cannot resist moisture as well as root covering can. When bark gets covered with soil it begins to decay at different rates depending on the species of tree and the other variable such as soil type and moisture content. It weakens the bark's ability to protect the tree from all the organisms that would invade the tree's system and many of these organisms are pernicious. So, keep the soil level at the right level, which is where the bark meets the root covering. This is easily seen on most species, because the bark is so much different from the root covering. If you have trouble locating the area just make sure the soil is lower rather than higher. Roots will grow bark to protect them, but root covering cannot easily replace bark, if it can do it at all.

Girdling Roots

As the tangled mass of new roots that emerged from the trunk increase in diameter every year they get closer and closer together because their position does not change, only the diameter changes. Soon enough they start to touch and merge. Something like welding takes place which results in even thicker diameter roots. Eventually they will look more like a solid sheet of wood. From the bottoms of these masses of roots sinker roots will grow. The sinker roots go down into the Earth and inevitably encounter the older, larger, better roots of the tree. The result is a mass of well anchored wood that interferes with the vital root system of the tree. This mass is dangerous to the tree and can result in damage to the tree and even death. This is caused by "girdling" of the tree's essential roots. Decay also causes symptoms and even death. Girdling works much like a rubber band works when put tightly around a person's arm. It cuts off the circulation. Trees have a system that flows in two directions but in ways that differ from our circulatory system and pressure around the root, trunk, or limb interferes with the system. When enough roots become girdled, the canopy of the tree will begin to die appearing much like it would if it were starving. The only cure I know is to excise the adscititious roots, a difficult to impossible procedure. This condition is so common I am compelled to dedicate myself to educating the public and cope with the problem wherever I encounter it.


Tree roots grow in any direction they are able to grow. There seems to be no central intelligence system that guides the placement of roots, or limbs either. When a root grows around the trunk of a tree a problem arises when the root gets larger. The trunk and the root increase in diameter every year and eventually pressure is created between the two tree parts. If the root applies too much pressure to the trunk the flow of fluids in the tree is halted or diminished. This root is called a "girdling root." I have put a picture of such a problem here. The root pictured has not become large enough yet to damage the tree trunk and can still be cut to prevent damage. However, the tree wasted a lot of energy growing that root and what is visible in the picture is only a fraction of its total root mass. Toward the end of the root branching occurs and the mass is greatly increased. This tree will loose a lot of roots when the girdling root is cut. Still, it is better to cut it than to leave it. One of my customers had me out to consult with him about his trees and I advised him immediately to excavate the root crown of his tree. He later called me back out for further consultation and I took this picture at that time. Notice the discolored bark. It goes up the trunk from the soil nearly a foot. The lower section of the discolored bark is nearly breached by decay. This tree was saved by that man's diligent efforts.

Root Crowns

One of the things I want everyone to know is that a tree enters the Earth via the root crown or root  flare. This is the enlarged area above the ground. It is wider than the trunk and can be likened to a golf tee set on the Earth upside down. It is shown in the photos and the drawings. If your tree does not have a visible root flare it is buried too deep. Look for parallel sides emerging from the Earth like they do on a telephone pole or a fence post. That is the sign of a buried root crown. A tree with no visible root flare needs to have the soil lowered. That means digging. It could be very difficult to do the digging. I have seen trees with the tangled root mass that grew in the new soil so dense that digging was impossible. In such a case the only thing that can be done not enough. It sometimes becomes necessary the use air tools to remove the soil from around the trunk and roots. The air tools do not damage the roots. Then the root mass has to be carefully cut with chain saws, hand saws, chisels and other innovative tools. As I said, even that is not enough. At best the tree might survive if enough of the mass can be removed to restore some of the flow from the roots. Don't be discouraged! Examples like the one I am referring to are rare. Usually it is just a matter of digging. Learn more at Root Crown Excavation in this website.


The result of digging out the root crown is a root well. Imagine a tree growing in a well that is only a few inches to a few feet deep. That is what you want if the soil is too high for the tree. You can line the sides of the well with rock or brick or something else that is inert. If the well is deep and soil does not drain fast enough you can install a drain in the well. Ultimately it comes down to your own creativity. I have seem some very beautiful root well.

I have to say, again, that the problem of buried root crowns is very common. Almost every home that has trees around it that were there before the house was built has buried root crowns. It remains a problem for many reasons, but one important one is the fact that the time required for a tree to demonstrate symptoms that arise from a buried root crown is so long that the cause of the symptom is lost in time. People move away and the new owners are left with a problem that they did not see created. Unless someone informs them or unless they already know, the trees will get worse and worse. Eventually they will call The Tree Tender or some other company because the tree is not doing well. By then the problem is pretty bad and sometimes uncorrectable.

I was called out to examine a huge live oak tree for a realtor. She said the prospective buyer was concerned that the tree had problems and since the tree was right in front of the front door and a very important part of the property he wanted to get an expert opinion about the tree. Well, the crown of this tree was about seventy percent dead and the rest was dying. It had a trunk that was about three feet in diameter and must have been about five hundred years old. There were big fungal conks growing from the base of the tree and little oak leafs growing all around the base of the tree. The root flare was partially visible, but much of it was under the soil and had been for about thirty to fifty years; it was impossible to determine more accurately. The poor trees was almost gone. I doubt if it lived and the prospective buyer declined the purchase. I have not been back to see what happened and I don't really want to see it. I know what I would likely find.

I am afraid I can go on about this far longer than you could maintain interest. So, let me close this article with a couple of pictures of a tree that I discovered growing in a creek bed in central Austin. I took these pictures with my cell phone camera in 2009. I knew I could use them in this article to demonstrate the fact that roots can cover themselves with bark if they become exposed. These trees were once growing on the bank next to the water. As the water eroded away the bank the trees became more and more exposed. It happened slowly enough for the trees to adapt. They had to put extra energy into anchoring themselves to the Earth and to protect their roots from the light, heat, air, and other threats. They did this very well. It is far from ideal, but they are still alive and I suspect they will live a lot longer.