Competitive Effects of Turfgrass on the Growth of Ornamental Shrubs1

Abstract

AbstractPlanting of a shrub or tree into a mature grass sod may result in poor establishment of the woody species. This experiment was designed to measure the field response of four species of ornamental shrubs to turfgrass competition. The shrubs used were forsythia (Forsythia intermedia zabel), azalea (Rhododendron X), Japanese barberry (Berberis thunbergi DC.) and taxus (Taxus media Rehd.). Turfgrass treatments included plots maintained at high or low rates of N fertilizer and receiving, in some cases, supplemental irrigation to maintain high soil moisture. Treatments with no turfgrass were either bark mulch or bare ground. Turfgrass plots were mowed regularly to a height of 7.6 cm. The effects of these variables were measured by evaluating several aspects of growth and development of each shrub species.Turfgrass established 2 years previously on an Enfield silt loam (Typic Distrochrepts) significantly suppressed the growth and development of all four species of shrubs as compared to plots where turfgrass was not a competitor. Differences in soil moisture or temperature are not believed to have been responsible for the differences observed in these findings. Plant competition for N was suggested by both the color ratings and analyses of leaf tissue of the shrubs during the first year of shrub establishment. Additional fertilizer, applied as a topdressing, was more beneficial to the turfgrass than to the shrubs, and did not significantly increase their growth in most cases. The addition of K and P did not increase growth in any of the treatments and apparently was not a factor in the competition between the grass and the shrubs.