Growth, survival, and aesthetic quality of boxwood cultivars as affected by landscape exposure

Abstract

Three cultivars of boxwood, 'Winter Gem' (Buxus microphylla Sieb. and Zucc.), 'Green Velvet', and 'Green Mountain' [B. sinica (Rehd. and Wils.) Cheng var. insularis (Nakai) M. Cheng x B. sempervirens L. 'Suffruticosa' L.], were planted in 12 different landscape exposures (N, ENE, NNE, E, SSE, ESE, S, WSW, SSW, W, NNW, WNW) at Manhattan and Wichita, Kans., representing U.S. Dept. of Agriculture hardiness zones 5 and 6, respectively. In Kansas, winter stress is often the greatest threat to plant survival, and Winter 1995-96 was one of great extremes. Official lows of -25 °C for Manhattan and -23 °C for Wichita were recorded, along with sharp 24-hour temperature drops of 31-32 °C in January and March. Differences in cultivar performance were noted between sites. Better winter quality was exhibited by 'Green Velvet' and 'Green Mountain', although significant bronzing occurred on the former in Manhattan. Locations on N, ENE, NNE, NNW, and WNW exposures resulted in better plant quality of all cultivars, whereas plant performance was poorer at S and SE exposures. Differences in canopy temperatures of up to 15.7 °C were recorded, on the same cold winter day, between NNW and ESE. Recovery from winter dieback and growth during Summer 1996 varied with cultivar, site, and exposure. 'Winter Gem' grew most in height, and 'Green Velvet' grew most overall at Manhattan. Growth rates were dependent on exposure, with greater growth at NNE, E, SSW, and WNW. Performance of 'Green Velvet' and 'Green Mountain' indicated that they could be used in any exposure with conditions similar to those of the test sites.