How much soil volume do trees need?
A. Large shade trees in downtown settings rarely, if ever, have sufficient soil volume to grow to their full potential size. Many models for predicting the volume of soil required have been proposed. In our region, a useful rule of thumb is that each inch of dbh (trunk diameter at 4.5’ above the ground) requires about 20-25 ft2 of open ground with uncompacted soil. However, you will find that this amount of soil is rarely provided. Trees do survive, but do not reach their expected size. A tree may establish and grow normally for a few years. Then, when there is no longer enough soil for the tree’s increasing size, growth dramatically slows and the tree declines prematurely. Some trees are able to overcome the situation by rooting under sidewalks and through cracks to access adjacent lawn areas.
