The Critical Root Zone

The Critical Root Zone (CRZ) of a tree is established on the basis of the trunk diameter. The CRZ is a circular area which has a radius of 12 inches to every inch diameter of trunk taken at 4.5 feet above grade. Root systems will vary both in depth and spread depending on size of tree, soils, water table, species and other factors. However, this CRZ description is generally accepted in the tree industry. Protecting this entire area should result in no adverse impact to the tree.

The above CRZ drawing has been further differentiated as the "Perimeter" (PCRZ) and "Interior" (ICRZ) to help illustrate potential impact and required Post care. Generally, the full PCRZ is considered the optimum amount of root protection for a tree. As one encroaches into the "Perimeter CRZ", but not into the "Interior CRZ" the greater Post Care the tree would require to remain alive and stable. The "Interior CRZ" is half the radius of the full PCRZ.

The absolute maximum disturbance allowed must still leave the "Interior" CRZ undisturbed if the tree is to have any chance of survival. This "Interior" CRZ would equal the size of a rootball needed to transplant this tree which in turn would require extensive Post Care and possibly guying. Post Care includes but may not be limited to; regular irrigation, misting, root treatment with special root hormones, mulching, guying and monitoring for several years.