The objective of the ordinance should be to specify size of trees to be planted, quality of trees and survival standards. A suggested approach is to specify the minimum size tree required in terms of trunk diameter, and set a minimum size container or soil ball associated with the minimum size. For instance, a minimum 2.5-inch basal caliper may be required in the ordinance. The ordinance would further specify that a container tree would be grown in a minimum of a 30-gallon container. This would avoid installation of 2.5-inch trees grown for excessive periods in small containers.
Trees grown for excessive periods in a container often have a pot-bound root system.
The roots on pot-bound trees are very slow to emerge from the root ball and establish in the surrounding soil. This makes the trees vulnerable to water stress and increases the chance of mortality in the first year or two after planting. The ordinance should specify a minimum percentage of large canopy trees in order to achieve a target canopy cover. A recommended minimum would be 60-70 percent large canopy trees. The minimum size for the canopy-type trees should be 2.5 inches to 3.0 inches basal caliper and for the small trees, 2.0 inches basal caliper.