Boxwoods are broadleaf evergreen shrubs belonging to the genus Buxus. They retain their foliage through all four seasons, providing consistent color and year-round visual interest in the landscape. This characteristic makes boxwood a reliable choice in landscaping, often used to create formal structure, define borders, or form dense, low hedges. Because the leaves are present constantly, boxwoods require specific care, particularly during colder months, to ensure they remain vibrant green.
Defining the Evergreen Nature of Boxwoods
Boxwoods are classified as evergreens because their leaves have a long lifespan, often lasting several years before being shed. Unlike deciduous plants that drop all their leaves seasonally, boxwoods shed their older foliage gradually throughout the year. The species name sempervirens, found in the common boxwood, literally translates from Latin to “always green,” reflecting this defining trait.
The ability to retain foliage is supported by the plant’s physical structure, which is adapted to survive cold and dry conditions. Boxwood leaves are small, dense, and possess a thick, waxy outer layer called a cuticle. This cuticle acts as a protective barrier, significantly reducing the rate of water loss, or transpiration, when water uptake from the soil is limited. The leaves also have a compact internal structure that allows them to continue the slow process of photosynthesis even when temperatures are low.
Common Boxwood Varieties
While all members of the Buxus genus are evergreen, different varieties offer unique characteristics regarding size, shape, and cold tolerance. Buxus sempervirens, known as Common or English Boxwood, is a traditional choice for formal gardens. It is generally best suited for moderate climates, typically USDA Zones 6 through 8. A dwarf cultivar of this species, Buxus sempervirens ‘Suffruticosa,’ is traditionally used for very low knot garden hedges.
For gardeners in colder regions, several hybrids have been developed to enhance winter hardiness. The ‘Green Mountain’ boxwood, a popular hybrid of Korean and English species, is known for its upright, conical shape and maintains color reliably in temperatures as low as Zone 4. Another variety, ‘Winter Gem,’ is a well-regarded Korean boxwood that performs well in cold climates, generally thriving in Zone 5. These cold-hardy cultivars are selected for their ability to retain a dark green hue throughout the winter, minimizing the common discoloration seen in less resilient types.
Maintaining Green Foliage Year-Round
Maintaining year-round green foliage centers on managing water loss, which is the primary stressor for evergreens in winter. Since the leaves continue to lose moisture through transpiration, but the roots cannot replenish it when the soil is frozen, the plant suffers desiccation. This condition, known as winter burn, results in bleached or brown foliage, particularly on the side exposed to winter sun and wind.
Preventing Winter Burn
Deep watering the plants in late autumn, just before the ground begins to freeze solid, is essential to prevent this damage. This ensures the plant’s tissues are fully hydrated, providing a reservoir of moisture to draw upon during the winter. Applying a two to three-inch layer of organic mulch around the base of the shrub after the ground freezes also helps conserve existing soil moisture and moderate root temperature.
Addressing Bronzing
Boxwoods may also experience a temporary color change called “bronzing,” where leaves take on a reddish-brown or yellowish cast. This is a natural stress response to cold temperatures, harsh winter sun, and wind exposure. To mitigate bronzing, plants should be sited in areas sheltered from strong winds or afternoon sun, or they can be protected with temporary burlap screens. While concerning, this bronzing is generally reversible, with the foliage returning to its vibrant green color once warmer temperatures and consistent soil moisture return in the spring.