Oak trees have a large root system with a volume sometimes greater than that of the branching part of the tree. The root system stabilises and feed the tree. However, the roots can be easily damaged or suffocated. If you learn about the root system of your oak tree, you can ensure that your oak's root will stay healthy and that your tree will live long and be able to survive drought.
An oak's root system begins with a long, deep taproot that penetrates the soil and absorbs water and nutrients as it develops its other roots. Oaks are known for their large taproots, which can draw water from deep under the earth, making them more drought-resistant. An established oak grows thick, lateral roots from its taproot, which rests about 4 feet deep and stabilises the tree. From the lateral roots grow small, fibrous roots that do most of the work of absorbing water and nutrients from the soil.
The root system's purpose is to uptake nutrients and water from the soil. A mature oak's roots can draw more than 50 gallons of water per day for the tree, some of which will evaporate through its leaves as a cooling process, similar to sweating in humans. The root system also stabilises the tree; damaged roots could result in the tree falling over.
An oak tree's root system can be damaged and traumatised if the ground above it is heavily trafficked, dug up, poured over with concrete or degraded with other high-impact activities. A lot of soil placed on top of the roots---more than 4 to 6 inches---will suffocate them. However, a light mulch layer improves the health of an oak tree's root system by aerating the soil around the roots and providing the roots with extra nutrients to distribute to the entire tree.
Roots and Earthworms
Earthworms can burrow for warmth among an oak tree's shallower roots in the winter months, 1 to 4 inches below the surface. They create tunnels that allow the oak's roots to better probe into the soil in the springtime.
Severed roots or roots near which steam pipes have been buried may result in the death of some tree branches, discolouration of the leaves or tilting. The roots can usually recover if fewer that ¼ of the roots are affected.
Oak Roots' Reach
An oak's roots are spread under the ground beneath the tree's drip line (the line where its branches end). They also expand about 1/3 farther beyond the drip line. However, the root production zone, the most important part of the root system to protect from damage, is only to about ½ the distance of the drip line from the trunk. Meanwhile, the area just around the drip line absorbs the most nutrients and water, so flowers should not be planted in the area.