Effect of Above and below Grade Planting On Four Landscape Trees in Southern California

Four landscape trees (Quercus agrifolia, Quercus virginniana, Schinus mole and Cinnamomum camphora) were planted in October 2008 at the following depths: 7.5 cm above grade; at grade; 15 cm below grade and 30 cm below grade. Trees were planted from nursery stock grown in 56 L containers.   All trees were irrigated three times per week by drip irrigation.  Trees planted below grade were planted with 2 cm diameter access tubes so that the buried root balls could be wetted directly without backfill/rootball interface issues.  Basal stem caliper size ranked from least to most growth were: Q. agrifolia, C. camphora, Q. virginniana and S. Mole.  C. camphora had an inverse linear response to planting depth: trees that were planted deeper grew less. Planting at 30 cm below grade resulted in smaller caliper size compared to other planting depths for all species.  Stem temperature for S. mole planted 30 cm below grade was higher than for other treatments, an indicator of stress for deeply-planted trees.