Effect of Soil Amendments and Planting Depth On Landscape Establishment of Live Oak.

Soil conditions are an important factor in the successful establishment of trees in the urban landscape. Planting depth, defined as the location of the root collar relative to soil surface, is also of concern for landscape tree establishment and varies substantially within the horticultural industry. The objective of this study was to determine the effect of four soil amendments and three planting depths on live oak (Quercus virginiana Mill.) growth and visual quality. Soil amendments were: native sandy loam soil (control), incorporated sand (30% by volume), incorporated composted peat (30% by volume), and sandy topsoil in raised (20 cm) bed. Trees were planted with root collars at one of three planting depths (7.6cm below grade, grade, or 7.6cm above grade). Plots with incorporated peat had significantly lower bulk densities when compared to plots with incorporated sand or with sand in raised beds. Plots with sand in raised beds and incorporated peat had fewer soil fungal colony forming units per dry gram of soil when compared to control and incorporated sand plots. Control plots had significantly less soil bacterial colony forming units per dry gram of soil than plots with incorporated sand. Visual quality of live oak roots was improved when planted in raised beds with sandy topsoil when compared to the control soil plots. Aboveground tree quality (shoot) was improved when planted in plots with incorporated sand and in raised beds with sandy topsoil, when compared to control and incorporated peat plots. Below grade planting resulted in reduced trunk diameter and a lower relative growth rate when compared to trees planted at grade or above grade. Therefore, we recommend planting live oaks with the root collar at grade in sandy top soils in raised beds to improve tree establishment.