These roots will often form spontaneously at the root collar from large woody roots. Although it is not known exactly what causes their formation, they usually develop as a result of injury. There are many misconceptions about root growth in trees. Horizontal root spread is one of the more important. It is often said that the majority of feeder roots are concentrated at the dripline of the tree.
Roots extend to that distance and much farther.
This is an important fact to remember when applying herbicides, fertilizers, insecticides, and other soil treatments around trees. Careful consideration can prevent serious injury to your trees. Another misconception is root depth. Roots will grow wherever the environment is favorable. They require water, oxygen, minerals, support, and warmth.