Influence of Mulches on Weed Control, Soil pH, Soil Nitrogen Content, and Growth of Ligustrum japonicum

Four organic mulches, screened pinebark, hardwood (primarily oak), cypress and decorative pinebark nuggets, applied at depths of 0, 5, 10, and 15 cm (0, 2, 4, 6 in) with or without an inorganic weed barrier fabric, were tested in field and container studies to determine their effect on weed suppression, soil pH, soil nitrogen content, and growth of Ligustrum japonicum. Results indicated that mulch applied at shallower depths, in combination with a weed barrier, provided optimal weed control without tying up soil nitrogen or reducing plant growth. Coarser mulches out-performed finer-textured materials. Most effective weed control was obtained with decorative pinebark nuggets with weed barrier fabric at a 15 cm (6 in) depth of application when compared to unmulched controls. As the depth of mulch was increased, soil pH, soil nitrogen content, and visual rating of plant growth decreased. Mulches over 10 cm (4 in) deep tended to inhibit plant growth, although optimum depth was dependent on the mulch material used.