Common Boxwood

Common boxwood (Buxus sempervirens, Buxaceae) is a slow-growing broadleaf evergreen shrub or small tree native to southern Europe, northern Africa, and western Asia. Left unpruned it can reach 15 to 20 feet tall (occasionally 30 feet) with a dense, multi-branched, rounded form and a spread of about 16 feet. Opposite, elliptic to oblong leaves (12 to 25 millimeters) are dark glossy green above and lighter yellowish-green below. Angular young stems are distinctive. Small, fragrant, apetalous creamy flowers appear in axillary clusters in spring, followed by small three-horned capsules.

Common boxwood grows in full sun to part shade on moist, well-drained loams (pH 4.5 to 8.5), hardy in Zones 5 to 6 depending on cultivar. It is resistant to rabbit and deer browse and responds well to mulching over its shallow root zone. Disease pressure matches littleleaf boxwood: boxwood blight, Phytophthora root rot, Volutella leaf and stem blight, leaf spot, canker, and black root rot are all documented. Pest associations include boxwood leafminer (to which 'Suffruticosa,' 'Argenteo-variegata,' and 'Pendula' show resistance), boxwood mite, boxwood psyllid, and scale insects. All parts are toxic. Notable cultivars include 'Suffruticosa' (Edging Boxwood, 4 to 5 feet), 'Arborescens' (Truetree Boxwood, 15 to 20 feet), 'Aurea Pendula' (weeping, variegated), 'Graham Blandy' (columnar), 'Skywalker,' 'Variegata,' and 'Latifolia Maculata.'

Boxwood in the Puget Sound lowlands is a bet against boxwood blight (Calonectria pseudonaviculata), which is endemic to our region. The pathogen thrives in our wet, cool conditions and spreads through water splash, contaminated tools, and nursery stock. Once established in soil, it persists for years. The first symptom is dark leaf spots followed by rapid defoliation. If you are committed to boxwood, cultural management is everything: avoid overhead irrigation, sterilize pruning tools between plants, and ensure good air circulation. Part shade reduces leaf scorch from winter sun and wind but increases humidity, which the blight pathogen loves. It is a tradeoff with no perfect answer. Boxwood psyllid and leafminer are chronic pests. For new hedges, consider Japanese holly (Ilex crenata) or Sarcococca as alternatives that fill the same design role without the blight risk. Volutella blight (canker) often co-infects with boxwood blight; look for salmon-pink spore masses on leaf undersides to distinguish. Boxwood is resistant to Armillaria root rot and can be replanted where Armillaria has killed other species (PNW Plant Disease Management Handbook).

— Chris Welch, ISA Certified Arborist