Boxwood (genus Buxus) is a highly valued evergreen shrub known for its dense foliage and adaptability in landscaping, particularly for formal gardens and hedges. While boxwoods are generally slow-growing, their eventual dimensions are not uniform. Their mature size is highly dependent on the specific species or cultivar selected. Understanding this genetic variability is the first step in successfully incorporating this classic shrub into any landscape design.
Boxwood Size by Species and Cultivar
The maximum size a boxwood achieves is genetically predetermined, meaning the species and cultivar selection is the greatest factor in its long-term dimensions. Boxwoods fall into three general size categories, from massive specimens to compact dwarfs. Maturity often takes 10 to 20 years to reach full size. The American or Common Boxwood (Buxus sempervirens) represents the largest end of the spectrum. Unpruned, this species can develop into a large shrub or small tree, frequently reaching 15 to 20 feet tall and equally as wide in ideal conditions.
A middle range of boxwoods, often used for standard hedges, includes the Korean Boxwood (Buxus sinica var. insularis) and many popular hybrids. Cultivars within the Korean Boxwood group, such as ‘Wintergreen,’ are moderate-sized, typically maturing in the range of 3 to 4 feet tall and wide. Cultivars like ‘Green Velvet’ and ‘Baby Gem’ are also common choices, forming dense, rounded shrubs that mature to a manageable 3 to 4 feet in both height and width. These varieties offer a good balance of form and size, making them suitable for foundation planting and medium-height borders.
At the smallest end are the true dwarf and miniature cultivars, which are perfect for edging or knot gardens. The classic Dwarf English Boxwood (Buxus sempervirens ‘Suffruticosa’) is a prime example, growing very slowly to only 1 to 2 feet tall and wide. This variety’s extremely slow growth rate, often less than two inches per year, allows it to maintain a compact size with minimal intervention.
Factors That Determine Boxwood Growth Rate and Final Dimensions
While genetic makeup sets the potential maximum size, environmental conditions directly influence the rate of growth and the final dimensions a boxwood achieves in a specific location. Boxwoods are notoriously slow-growing shrubs, with most varieties adding only 3 to 6 inches of new growth annually under optimal conditions. Dwarf cultivars exhibit an even slower rate, sometimes growing only half an inch to one inch each year. The amount of sun exposure significantly affects a boxwood’s density and growth habit.
Although many varieties tolerate full sun, they thrive best in locations that receive partial or dappled shade, especially protection from intense afternoon sun. Plants grown in excessive shade tend to develop a more open, less vigorous habit, while full sun can increase their susceptibility to winter injury and bronzing.
Soil quality and drainage are fundamental elements in determining the plant’s overall health and size. Boxwoods have shallow root systems that require well-drained soil; poor drainage is a common issue that can lead to root rot and stunted growth. Providing consistent moisture encourages a healthy root system, though established plants are generally tolerant of drought conditions. A lack of necessary nutrients, particularly nitrogen, can also slow the growth rate and cause yellowing of the older, inner leaves.
Managing and Controlling Boxwood Size
Pruning is the primary tool for size control, often necessary to maintain boxwoods at a size smaller than their mature potential, especially when used in formal settings like hedges. The method used is important for the plant’s long-term health. The ideal time for general pruning is in the early spring, before the main flush of new growth, or after this initial growth has occurred, typically around early June.
For routine size control and a formal look, thinning is preferable to surface shearing. Thinning involves selectively cutting longer branches back to a main stem, which allows sunlight and air to penetrate the interior. This practice promotes interior foliage growth and reduces the risk of fungal diseases, which are common in dense, sheared shrubs. Shearing the outer surface creates a thick shell of leaves that shades the interior, often leading to a hollow, weak center.
If a boxwood has become significantly overgrown and requires a major size reduction, a process called rejuvenation pruning must be used. To prevent shock and maintain the plant’s health, no more than one-third of the total canopy mass should be removed in a single year. This severe reduction should be phased over two or three growing seasons until the desired size is achieved. Avoiding any pruning in late summer or early fall is important, as the resulting new growth will not harden off sufficiently before winter and will be susceptible to cold damage.