A large proportion of a mature tree's roots are in the top metre of soil, where they have access to oxygen, water, and nutrients.  In their search for these essentials of life, the roots may extend horizontally well beyond the drip line at the edge of the tree's canopy. (The drip line is where water would drip of the outermost leaves on the tree.)   Though hidden below ground and often ignored by gardeners, roots are vital to a plant's survival and growth. They absorb water and nutrients and help move them throughout the plant; they store food for future use; and they anchor the plant in the soil. (Nutrients are the chemicals that plants need to use as food).

As they go looking for water and nutrients, roots grow through the soil away from the center of the plant. This growth takes place in the root tip where cells are actively dividing and elongating. Just behind the tender root tip, which is protected by the root cap, is a zone of cells that produce many tiny projecting root hairs. These are in direct contact with the soil and increase the surface area available for absorption of water and nutrients. Have a look at the microscopy site to see some hugely enlarged pictures of roots and root hairs!

If they are exposed to sunshine or dry air, the root hairs quickly shrivel and die. When plants are dug up by people or animals, they will quickly wither and die.

Plants are anchored in the soil by fibrous roots, taproots, or (sometimes) a combination of both. A fibrous root system has many branching roots that grow fairly close to the soil surface. The taproots of some large trees and shrubs, in contrast, grow deep into the soil and develop horizontal branches that hold the plant firmly in place.

. . . . . . . . . . . . . . . ..
(A fibrous root system to the left, and a tap root to the right)

Adventitious Roots and Stems

Adventitious roots are roots that grow in unexpected positions, such as from leaves or the sides of stems. Strawberry stems ("runners"), for example, form adventitious roots as they spread across the ground. This means that new plants can be formed as the stems reach across the soil to new positions. These new plants will be joined to the main plant at first (but can be cut free when the roots have developed properly), and will be exactly the same as the original plant.