The tap root may grow vertically for some considerable distance if soil conditions are favorable. As the root system continues to enlarge with tree growth, the root type becomes less recognizable. Below ground environmental factors including moisture, oxygen supply, soil texture, below ground obstacles, other roots, and animals determine the ultimate shape and extension of the tree s root system. Most Tree Roots Are Found in Top 18 Inches Healthy trees have extensive root systems. Usually, more than 50 percent of a tree s roots are in the top six inches of soil.
Roots extend laterally for considerable distances.
Root systems may occupy an area four to seven times the surface area occupied by the crown of the tree. Soils with higher clay content have less extensive roots than soils which are sandy or better drained. Trees growing in mulches or in a natural woodland environment will have more roots closer to the surface than trees growing in turfgrass environments. Roots growing in fertile, moist and well aerated soils will be more numerous, less extensive and closer to the trunk than roots in less desirable soil. Roots in sandy soils will be more extensive, less fibrous and fewer in number.