The Root of the Issue for Trees

There are many misconceptions about roots, such as the roots of trees being strictly outside the drip line (outer branches) of the trees, or that trees have a tap root that grows deep into the earth. I hope I can shed som

e light on this dark and mysterious aspect of trees. 

Besides anchoring the tree to the ground and storing extra sugars and other precious nutrients, the main purpose of roots is to actively collect resources. Trees are extremely good at seeking out resources such as water and minerals and developing the root structures to better collect them for the tree as it matures. I should mention that this process is complex and beautiful, with cross species cooperation such as mycohrizae fungi and beneficial bacteria doing a lot of the leg work for trees in exchange for precious sugars. But trees themselves also have developed amazing behaviors that help them capitalize on a store of resources in the soil. 

One interesting attribute of certain trees is their ability to manipulate the environment just around their roots, an area called the rhizosphere. They can alter the pH of the soil in this microscopic space, allowing the polarized nutrients to become more available. This specific ability is what gives our native trees a leg up in our highly alkaline soils. Eastern varieties do not have this ability in our area because they are use to their native acidic soils, where nutrients in the soil are more bioavailable. 

Roots are also keen to find water. They will send roots to areas that get consistent water, and shy away from areas that get too much. We’ve all seen this when hiking near a stream. Giant cottonwoods will reside on the banks of irrigation ditches without crossing that boundary into the perennial water zone. Instead, their roots remain on the side of the ditch where they get incremental water. If you hike in the desert you will also see junipers sending out long rope-like roots towards the dry river bed, where during rainy season, they may get a much needed drink of water. 

So where are the roots? They are where the resources are. For trees growing in a open field, this will look different than for trees growing in a forest, which will look quite different than a tree growing under weed fabric and gravel. Don’t be fooled, the roots can also extend out 2 or 3 times the height of the tree away from the trunk, or down tens of feet into the soil if that is where the nutrients and water are. In fact, the deepest roots ever found were 120 meters deep, found in the Echo Caves of South Africa. 

Now that we have established the resource-seeking behavior of trees, let's back up and say that some species of trees will follow certain patterns of root architecture. Some trees have a flatter root plate pattern, some trees have large lateral roots, with sinker roots coming off of those, some have an overall heart shape, while others have a longer tap root. 

When I was working at the tree farm, some of the hardest trees to dig up with our machines were the Oak trees. Without root pruning during the trees’ development the tree will develop a large tap root that is sometimes impossible to sever with a machine. Many times we would have to give up on the tree and leave it where it was. However, there is a limit to how deep a tree’s roots will usually develop. This is mostly due to the lack of oxygen, water or resources as the soils get deeper. There are exceptions to everything as mentioned earlier. 

Now, if you buy an oak tree from a nursery or tree farm it will have gone through a process of root pruning during either its development in the nursery or in the process of digging it to put it in your yard. Therefore, the root architecture of trees that are put in modern landscapes is completely different than those in the wild. Furthermore, the soils of modern landscapes are very different than those in a forest. Often, soils in the urban environment are compacted and lacking in organic matter. Along with irrigation and fertlization, this will severely stunt the development of the roots over time. Many times the tree will reach a mature height without developing an extensive root system to support it, which leads to the tree falling over in heavy winds when the ground is fully saturated. So, it is hard to make assumptions on root architecture and structure in the landscape setting. 

Another misconception is the idea that there are no roots underneath the center of the tree. All the roots are outside the drip line. In fact trees have a pattern of sending out roots at a

young age away from the tree, then later in their development they revisit this prime location. For this reason, pesticide applications are often made near the root collar. We know that the trees has at least some roots there while it is unlikely there are roots of another plant in that same area. 

People often ask me if they should remove the wire basket from the tree when planting a balled and burlaped tree. The answer is a little complicated, but fascinating. When a tree is growing near a barbed wire fence, with the fence perhaps nailed to the bark of the tree, the tree will begin to envelope the fence as the tree grows in diameter. We also see this when dog toys or lawn ornaments have been left in the branch crotches of trees. Unfortunately, toys or wires that completely circle the tree can girdle the tree and kill it. If roots interact with a similar obstruction they do something completely different. The obstruction will split the root, with each half of the root bypassing the obstruction and continuing to grow as it was, in the same direction. This process is called deflection. It makes sense that trees would develop this habit, since they are often seeking out territory away from the tree. 

So if a wire basket is left on the tree it may induce the tree to deflect more than if it was removed at planting. Does the deflection hurt the tree? Probably not. If anything it will probably create more of a smaller diameter, fibrous root system, which may have issues for other reasons. More important than removing the wire basket, is removing the twine that holds the basket together. Often this twine is nylon based and will not break down over time. So like a wire, or a circling root, the twine will eventually kill the tree. Similarly, roots that grow in a circle, such as those grown in a plastic container can eventually girdle the tree as it develops. This is why root pruning is crucial when planting container grown trees. 

The main components of carbohydrates formed from photosynthesis are CO2 and H2O and sunlight. Essentially half of the equation comes from the ground. So why so we focus so much of the above ground aspect of the tree while ignoring what’s going on underground? As a certified arborist, we are trained to identify fine root hairs that indicate healthy roots, we are taught soil sciences, we understand the basic needs of organic matter and water and air that make roots healthy, and the nuances of which trees like what soils. 

If you suspect your tree is suffering due to what is happening underground, please call a certified arborist to examine your soils — it takes an expert to find the deeper issue!