Influence of Lime and Micronutrient Amendments on Growth of Containerized Landscape Trees Grown in Pine Bark

Growing landscape trees in containers is a common practice in the nursery industry. In the southeastern United States, pine bark is often used as a container substrate, and two common amendments to pine bark are lime and micronutrients. In this study, three experiments were conducted to determine the effect of these amendments on the growth of a wide range of landscape tree species grown in pine bark. In the first experiment, nine species of landscape trees [Acer palmatum (Japanese maple), Acer saccharum (sugar maple), Cercis canadensis (redbud), Cornus florida (flowering dogwood), Cornus kousa (kousa dogwood), Koelreuteria paniculata (golden-rain tree), Magnolia x soulangiana (magnolia), Nyssa sylvatica (blackgum), and Quercus palustris (pin oak)] were grown from seed in two pine barks: pH 4.7 (low) and 5.1 (high). Preplant amendment treatments to each pine bark (Pinus taeda) were: with or without dolomitic limestone (3.57 kg.m-3) and with or without micronutrients (0.9 kg.m-3, Micromax™). The same experiment was repeated using Koelreuteria paniculata and Quercus palustris, the same lime and micronutrient treatments, and two pine barks: pH 5.1 (low) and 5.8 (high). In both experiments, micronutrients increased shoot dry mass and height for all species, while lime decreased shoot dry mass and height for all species. Effect of bark type in the first experiment was variable, while shoot dry mass and height were highest in the low pH bark when the experiment was repeated. Substrate solution element concentrations increased when micronutrients were added, decreased when lime was added, and in general, concentrations were higher in low pH bark than in high pH bark. In the third experiment, Koelreuteria paniculata was grown from seed in pine bark amended with 0, 1.2, 2.4, or 3.6 kg.m-3 dolomitic limestone and 0 or 0.9 kg.m-3 micronutrients (Micromax™). Initial pH for each lime rate was 4.0, 4.5, 5.0, and 5.5, respectively. Adding micronutrients increased shoot dry mass and height. Lime increased growth only at the 1.2 kg.m-3 rate. In general, substrate solution element concentrations increased when micronutrients were added and decreased when lime was added. In all three experiments, adding micronutrients was necessary regardless of pine bark pH, while adding lime was not necessary.