Evaluating Landscape Performance of Six Native Shrubs as Alternatives to Invasive Exotics

Abstract

There is increased interest in using native plant alternatives to invasive species for landscaping. Several invasive shrubs are used extensively in landscaping since they perform well in challenging landscapes, such as parking lot island plantings, which are dry, nutrient-poor, and sun and heat exposed. This study evaluated the landscape suitability of six underused Connecticut native shrubs [american filbert (Corylus americana), buttonbush (Cephalanthus occidentalis), northern bush honeysuckle (Diervilla lonicera), steeplebush (Spiraea tomentosa), sweet fern (Comptonia peregrina), and sweet gale (Myrica gale)] by planting them in a large commuter parking lot on the University of Connecticut (UConn) campus in Storrs. Two nonnative invasive species, ‘Crimson Pygmy’ japanese barberry (Berberis thunbergii) and ‘Compactus’ winged euonymus (Euonymus alatus), were also planted as controls. Buttonbush, sweet fern, and sweet gale performed as well as controls and had aesthetic quality index (AQI) ratings similar to controls throughout the study, which spanned three growing seasons. These findings were surprising for buttonbush and sweet gale, which are found in the wild occupying predominantly wet areas. Buttonbush plants readily established at the site as indicated by a 930% increase in plant size over the first growing season. Sweet fern and sweet gale produced attractive, dense, and uniform mounds consistently throughout the study. Northern bush honeysuckle and american filbert were slower to establish, but by the second and third year, respectively, plants were highly attractive and had AQI ratings similar to controls. Despite its attractive floral display, steeplebush performed poorly and developed powdery mildew (Sphaerotheca) symptoms in the first and second years, which contributed to a lower AQI compared with controls. Aesthetic quality for american filbert, buttonbush, and steeplebush was reduced because of variation resulting from seed propagation. For certain native species, plants received from the nursery were not robust, which may have had a greater influence on establishment and early performance than their inherent landscape adaptability. This study identified five underused native shrubs that are adaptable and able to replace invasive plants in landscapes.