Lime and Micronutrient Additions to Pine Bark Affect Growth of Nine Landscape Tree Species

Abstract

Although the practice of amending a pine bark substrate with lime and micronutrients is common in the nursery industry, the effect of these amendments on the growth of container-grown landscape trees has not been documented. The objective of this study was to determine the lime and micronutrient preferences for a wide range of landscape trees grown in pine bark. Approximately 10 seedlings per pot for each of nine species of trees were greenhouse-grown in pine bark-filled 3-gal containers. Initial pH of the bark was 4.7. Preplant bark treatments were: unamended (control), dolomitic lime only (3.57 kgμm–3), micronutrients only (Micromax™, 0.89 kgμm–3), or lime plus micronutrients (previously stated rates). All seedlings except one per pot were harvested at week 12, and shoot height was determined. Remaining seedlings were grown until week 19, at which time final shoot height was determined. Bark solutions were extracted (pour-through method) at week 7. Adding micronutrients increased height for all species by week 19. Adding lime either had no effect on height or supressed height. Micronutrient additions increased solution concentrations of Ca, Fe, Mn, Cu, and Zn, but in the presence of lime these increases were diminished. Under the conditions of this experiment, amending pine bark with micronutrients is essential for maximum height of these tree species, while a lime amendment is unnecessary.