Specifying Soil Volumes to Meet the Water Needs of Mature Urban Street Trees and Trees in Containers
Patricia Lindsey and Nina Bassuk
Abstract: The small volume of soil in a typical street tree pit or container often is not capable of supplying adequate water as the tree needs it. As a result, trees can experience severe limitations upon healthy growth and development. Current soil volume estimations fail to address three problems: 1) how to predict whole tree water use, especially for a wide range of prevailing climatic conditions, 2) now to tie this prediction to some easily measured tree parameter, and 3) how to incorporate both of the above into some simple yet accurate means of estimating soil volume. A weatherbased methodology for adequately sizing soil volumes is presented to address these concerns. This incorporates the findings of a recent study indicating that whole tree water loss can be reasonably predicted with knowledge of evaporation from a U.S. Weather Bureau Class A pan. A soil volume of 220 ft3 for a medium sized tree is then calculated. For use as a general estimate, 2ft3 of soil per 1ft2 of crown projection is recommended.