The Japanese Boxwood (Buxus microphylla japonica) is an evergreen shrub frequently used in landscape design for hedges and foundation plantings. Its dense, bright green foliage adds structure and year-round color to a garden setting. While often seen neatly manicured, the ultimate size a Japanese Boxwood can attain is highly variable, depending on its inherent genetics and human intervention. Understanding these factors is important for integrating this versatile plant into an outdoor space.
Typical Mature Size and Growth Rate
If left unmanaged, the Japanese Boxwood possesses the genetic potential to become a substantial shrub. The typical unpruned mature size falls within the range of 6 to 10 feet in both height and width, creating a large, rounded specimen. This size is generally reached over a period of many years, often a decade or more.
The natural growth rate of Buxus microphylla japonica is classified as slow to medium, which is a significant factor in its suitability for formal hedges. Under good growing conditions, it typically adds between 8 to 12 inches of new growth per year. This slow pace means the plant maintains its shape for a long time between trimmings, making maintenance less demanding than with faster-growing species.
The Impact of Cultivar Selection
The most significant determinant of a boxwood’s final size is the specific variety, or cultivar, chosen for planting. Plant breeders have developed numerous selections of Japanese Boxwood that mature at different sizes. Selecting the correct cultivar is the easiest way to ensure the shrub naturally fits its intended space in the landscape.
For instance, the standard Japanese Boxwood can reach heights of 6 to 8.5 feet and widths exceeding 10 feet, forming a sizable screen or backdrop. Conversely, dwarf cultivars like ‘Morris Dwarf’ are bred to remain very compact, often maturing at less than 1 foot tall and wide, making them ideal for edging or small containers. Other selections, such as ‘Green Beauty’ or ‘Winter Gem,’ typically stay in the 4 to 6-foot range.
Controlling Size Through Pruning and Maintenance
While genetics set the potential upper limit for size, pruning is the primary tool used to manipulate a Japanese Boxwood’s actual dimensions and density. Intentional size management ensures the shrub remains well within the boundaries needed for foundation plantings or formal hedging. Homeowners often employ two main pruning methods: shearing and thinning.
Shearing involves using hedge clippers to uniformly cut the outermost layer of foliage, which encourages dense new growth and maintains a crisp, formal shape. This repeated trimming effectively limits the shrub’s size over time, but it requires frequent application during the growing season. This method should be supplemented with occasional thinning.
Thinning involves reaching inside the shrub and removing small branches back to a main stem or a larger lateral branch. This technique allows light and air to penetrate the plant’s interior, which is necessary to prevent the center from becoming bare and woody. When reducing the overall size of an overgrown boxwood, it is generally recommended to remove no more than one-third of the plant’s total mass in any single pruning session to maintain its health and vigor.