How deep do tree roots grow?
Tuesday 16th July 2019
Holding up a tree is a tall order, but it's often achieved by surprisingly shallow roots. Most trees don't have a taproot, and most tree roots lie in the top 18 inches of soil, where growing conditions tend to be best. More than half of a tree's roots usually grow in the top 6 inches of soil, but that lack of depth is offset by lateral growth. For example, the root system of a mature oak can total hundreds of miles in length. Something to bear in mind when planting trees close to your property.
Still, tree roots vary widely based on species, soil and climate. Bald cypress, for example, grows along rivers and swamps, and some of its roots form exposed "knees" that supply air to underwater roots like a snorkel. Similar breathing tubes, called pneumatophores, are also found in the stilt roots of some mangrove trees, along with other adaptations like the ability to filter up to 90 percent of salt out of seawater.
On the other hand, some trees do extend remarkably deep underground. Certain types are more prone to grow a taproot — including hickory, pine and walnut — especially in sandy, well-drained soils. Trees have been known to go more than 20 feet (6 meters) below the surface under certain conditions!