Roots are the underground branches of the tree. They reach down into the ground to get the minerals and water for the tree's growth. The roots also anchor the tree in the ground. A tree's roots are its foundation and will keep pace with the size and dimension of the tree it will support.

The more the branches grow and expand in the crown, the more they grow deep and wide under the ground. The tree's roots form an amazingly intricate and complex system. Root tips may be covered with fine hairs to make it easier for the tree to absorb water and minerals. Trees absorb small amounts of moisture from the air through their leaves and their bark. Most of their water, however, comes via the roots.

Water enters the roots through thin membranes at their tips. The tree's vascular system draws the water up through the trunk and distributes it to the leaves. The leaves use the water to dissolve minerals. Excess water goes back to the air through pores in the leaf - a process called transpiration.

Roots are made up of a number of specialized components. The root hairs, tiny structures extending from the main root stems, have very thin walls which absorb water and minerals. This mineral solution is passed into the vascular core of the root from where it is transported throughout the tree. At the tip of the root, there exists a protective structure called the root cap. These loose cells are shed as the root grows into the soil.

Different trees have slightly different root systems. Some trees, such as the pine, have a strong central root called the taproot. This is usually larger than any other roots and often extends deep into the ground. Because substantial damage to this root can be fatal to the tree, trees with taproots are generally difficult to transplant. Other trees, such as the elm or maple, do not have a dominant taproot. Their root systems are characterized by a large number of roots often closer to the surface.

Generally, root growth is influenced by moisture and gravity. In other words, unless there are substantial amounts of moisture near the surface, roots tend to grow downwards through the soil. Roots are always growing and, like a tree's trunk, they grow both longer and wider. At the tip of the roots, the growing region is called the meristem. This is where most of the lengthwise growth takes place. In addition to this, wood is added to the inside of the root and phloem is added towards the outside.