How deep a root system penetrates the soil is dependent on moisture, temperature, composition of the soil, and the specific plant. Most roots actively absorb water and minerals. Although the “feeder roots” of most plants are found in the upper 3 feet (1 meter) of the soil, those of many trees are mainly in the upper 6 inches (15 centimeters) of the soil—the part of the soil richest in organic matter. In general, the lateral spread of a tree’s root system is four to seven times greater than the spread of the crown of the tree.