How Deep Do Tree Roots Go & What Does It Depend On? The Interesting Answer
Most of us know that a tree’s roots are like its heart, performing numerous essential functions to keep a tree alive as well as help it thrive. How far a tree’s roots go depends on the type of root we’re talking about. Tree roots can vary in depth from 4 inches up to 6 feet! After all, there are five types of roots! The most important three are the taproot, lateral roots, and oblique roots, but sinker roots and fine roots are essential offshoots of the first three. Let’s learn more about how deep a tree’s roots go down below.
Types of Roots and What They Do
Root type and depth are wildly variable depending on the tree’s size, but there are some averages we can refer to for a better picture of how deep the different root types grow. Let’s briefly check those out and then get into what these roots each do and where you’ll find them.
|Root Type||Average Root Depth|
|Lateral root||15 cm/5.9 in.|
|Oblique root||20-50 cm/7.9–19.7 in.|
|Sinker root||Up to 6 ft.|
|Fine root||10 cm/3.9 in.|
Depending on the tree’s growing conditions, including soil, sun, and watering, roots in mature trees can reach deeper than 6 feet into the soil.
Each of the roots has its own specific purpose, working together to anchor the tree and provide nourishment for the tree’s ongoing growth. Roots also store energy, tap nutrients, and interact with other roots and soil-dwelling organisms. Here’s a brief overview of what each of these five roots does:
Five Major Roots by Function:
- Taproots: The main root every other root stems from, the taproot acts as a deep initial anchor to provide the tree with stability, water, and nutrients. Most other tree roots outgrow the taproot over time.
- Lateral Roots: These are the shallow roots immediately under the soil, which spread outward up to 2 or 3 times the radius of the tree.
- Oblique Roots: Despite the fancy name, oblique or heart roots serve the same purpose as lateral roots but grow diagonally in the soil.
- Sinker Roots: These are secondary roots that spring from lateral or taproots, so they may be found in shallow soil or deeper down where they can send up hard-to-access water and nutrients.
- Fine Roots: Defined as any root smaller than 2 millimeters in diameter, fine roots spring from other main roots and make up the bulk of a tree’s water/nutrient delivery system. Fine roots are also the main mechanism that trees use to form symbiotic partnerships with beneficial fungi.
How Far Do Tree Roots Spread?
People have gotten so focused on how deep tree roots go that they underestimate just how wide they can be. Shallow lateral, oblique, and fine roots can reach as far out as two to three times the dripline of a tree. You can quickly identify the dripline as the outer circumference of where a tree sheds water after rain. From the trunk to that perimeter, multiply by two or three.
That can mean a mighty oak tree’s roots may go up to 90 feet away from the trunk, while the weeping willow’s root system can spread as far as three times the tree’s height. By contrast, the trident maple is often planted in urban areas because it has a shallow, compact root system and tolerates air pollution well.
What Happens to Tree Roots When a Tree Is Cut Down?
Tree roots typically go dormant after the tree is cut down because, without leaves, the roots have no way to photosynthesize and heal the damage. If there are above-ground roots, those may sprout new branches. In time, a small sapling could grow from the remnants of the tree.
More likely is that the roots and stump alike will simply die over time. Once dead, the stump and roots will rot and become both food and host for numerous organisms in the local ecosystem. Bugs and fungi particularly like rotted tree stumps and roots.
Tree roots are the arteries of a tree and its only method of gathering water and nutrients from the environment. Most tree roots are fairly shallow, though the taproot and sinker roots can reach down 6 feet or more.
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