The depth to which the root system penetrates the soil is dependent on moisture, temperature, the composition of the soil, and specific plant. Most of the roots actively absorbing water and minerals, the “feeder roots,” are found in the upper 3 feet (1 meter) of the soil. The feeder roots of many trees are mainly in the upper 6 inches (15 centimeters) of the soil—the part of the soil richest in organic matter.