Tree roots are very adventurous and will only grow and penetrate where it is easiest to grow, such as loose soil and mulch. Most trees do not have a taproot, and most tree roots are in the top 18 inches of soil, where growth conditions are usually best. More than half of the tree’s roots usually grow in the top 6 inches of soil, but this lack of depth is made up for by lateral growth.
Oak tree roots rarely go deeper than 18 inches beneath the soil. Oak trees, as with most others, have root systems that spread outward rather than downward. This provides them with superior anchoring and resource reach, but it reduces the number of plants that can grow in their vicinity.
Later, lateral roots begin to form that extend up to 90 feet from the base of the trees and become shallow, remaining up to 18 inches from the soil surface. Oak roots typically extend no more than 3 feet below the ground and no more than 2 feet below the surface in shallow soil. The roots that feed the trees are usually found throughout the soil that is under the canopy of trees, no more than 3 feet (1 meter) from the surface.
Growth Expectations for Ideal Conditions
Under ideal soil and moisture conditions, roots have been observed to grow to depths of over 6 meters. In general, tree roots grow no deeper than 1–2 meters (3–6 ft) below ground level, although in ideal soil conditions, the root system of some deep-rooted trees can reach 4 meters (13 ft). However, the roots may not grow as deep as one would expect from a tree that can reach over 100 feet in height.
It may not grow very deep, even taking into account the “lead roots” that can grow on the sides, but the lateral root system can grow at least as wide as the canopy, and some experts suggest the tree can cover an area three times larger than the canopy.
The main lateral roots grow laterally from the top of the taproot, very close to the surface in spruce and fir, but in oak they first bend to a depth of about 10 cm and then grow horizontally. Lateral roots are the main support of mature trees and can grow up to 90 feet from the trunk of a large tree. These roots grow outward from the trunk, forming an extensive web that becomes thicker and woodier over time, especially near the soil surface.
Other types of roots, such as oaks, can be harmful because their roots thicken as the tree ages. With relatively shallow roots, oaks are among the trees most likely to damage nearby paved surfaces. Oak roots can cause injury and damage to buildings, paved surfaces, and pools if the tree grows within 20 feet of a building.
Oak Trees Have Shallow Roots
Unlike pines, oaks and elms have shallow roots that can potentially damage foundations. Where the soil is filled with clay or the water table is high, oak trees will also develop smaller roots and more of them. It appears that where soil erosion has exposed roots, roots are actively growing into these oak trees, anchoring the tree. The large tree roots that usually come out from under the soil surface serve mainly as anchors for the oak.
As the oak matures, especially in naturally dry areas during the summer, deep vertical roots form on the sides, usually within three meters of the trunk. The roots within the first 20 feet of the trunk are important supports that hold the tree upright.
If more roots are removed, the plate roots that support the vertical structure of the trees will be adversely affected. Once a tree is cut down, its roots can no longer grow because the leaves are needed to nourish the roots.
As the trees grow, this original root is replaced by a large lateral root system that extends horizontally from the trunk to the drip line and far beyond, sometimes up to 90 feet. For a mature oak, this horizontal root system is the main support of the tree for the rest of its life. The deepest root of the oak is taproot, which usually grows directly under the trunk to a depth of 3-5 feet (1-1.5 meters).
Most Trees Have Shallow Roots
Most trees have shallow roots, with almost all roots within the first few inches of the soil surface, and their deepest taproot is usually no more than a meter or two deep. Most of the tree’s roots, including its taproot and heart roots, grow in the first three feet of soil and extend much wider than the drip line (an imaginary line that marks where water drains off the tree’s leaves). a tree is the roots of a tree, consisting of lateral roots that grow laterally just below the soil surface, and sometimes a vertical tap root.
Instead of growing straight down, palm roots prefer to grow horizontally and spread within the topsoil. Palms have a fibrous root system where a few narrow roots expand and spread into the soil rather than growing down. Palms do not have a tap root; instead, roots emerge from the area of origin and spread horizontally around the tree within the first 36 inches of potting soil. Most trees will never grow a taproot, instead opting for a sprawling network of tree roots and forage that is only 12 to 24 inches long.
Instead of thinking of oak roots as a mirror of above ground branches, imagine a web of shallow roots reaching far and wide to collect nutrients and hold oaks in place. Deep growing vertical roots take advantage of deeper soil moisture and add stability to an increasingly massive tree.
Roots usually start growing to the top of the tree, although root growth is cyclical and responds to environmental changes such as soil depth, water supply, aeration, mineral supply, and temperature. Oak roots are deflected and begin to grow downwards when they encounter looser bulk soil near the foundation, despite naturally growing horizontally.