Boxwood shrubs are evergreen, retaining their foliage throughout the entire year and providing structure and color in the landscape even during the winter months. The genus Buxus is a collection of dense, woody shrubs and small trees popular for formal hedges and ornamental topiary in many different climates. This year-round retention of green leaves separates boxwood from deciduous plants, which shed all their leaves seasonally. Boxwoods are favored for creating permanent garden boundaries and foundational plantings.
How Boxwood Retains Its Foliage Year-Round
Boxwood maintains its leaves through specific biological adaptations that minimize water loss. Unlike deciduous plants, boxwood leaves are designed to withstand the harsh conditions of cold and drought. The primary defense is a thick, waxy layer known as the cuticle, which covers the surface of each small leaf. This cuticle acts as a highly effective waterproof barrier, drastically reducing the rate of water vapor escape through transpiration.
The small size of the boxwood leaf is an adaptation that reduces the total surface area exposed to drying winds and winter sun. While boxwoods do shed older leaves, they do so gradually over the course of a year, not all at once in a seasonal drop.
This continuous leaf retention permits the plant to continue a low level of photosynthesis during mild winter periods. However, this evergreen nature also presents a challenge because the leaves are constantly losing some moisture. If the ground is frozen, the roots cannot replenish the lost water, leading to desiccation, which is the main cause of winter damage.
Popular Boxwood Varieties and Their Climate Needs
The success of a boxwood remaining green through the winter depends significantly on selecting a variety suited to the local climate. The term “boxwood” covers a wide range of species and cultivars, each with different levels of cold hardiness. Gardeners must consult the USDA Hardiness Zones to ensure their chosen variety can survive the minimum temperatures of their region.
For instance, the common or American Boxwood (Buxus sempervirens) is widely adaptable and includes cultivars like ‘Green Mountain’ and ‘North Star,’ which thrive in zones 5 through 9. These varieties generally maintain excellent green color throughout the winter. Conversely, some Littleleaf Boxwoods (Buxus microphylla), such as ‘Winter Gem,’ are also hardy in zones 5 to 9, but their evergreen appearance can be compromised in the coldest parts of their range.
In extremely cold regions, specific cultivars bred for superior cold tolerance, often derived from Korean Boxwood (Buxus sinica var. insularis), are recommended. If a variety is pushed past its cold-hardiness limit, the foliage may exhibit “bronzing,” a reddish-brown or yellowish discoloration that occurs as a stress response to cold or sun exposure. Choosing a cultivar known to resist this winter bronzing is necessary for a consistently green appearance.
Practical Care for Maintaining Evergreen Appearance
The biggest threat to a boxwood’s year-round green appearance is not the cold itself, but the combination of cold, wind, and sun. This environmental stress leads to winter burn, where the exposed leaves dry out and turn brown or yellow. Reducing this desiccation damage is necessary for maintenance in challenging climates.
Proper site selection is a primary preventative measure. Plant boxwoods on the north or east side of a structure to shield them from harsh, direct winter sun and drying winds. Providing adequate moisture in the late fall significantly increases the plant’s winter resilience. Deeply watering the shrub until the ground is frozen allows the plant to store water in its tissues for use during the winter when the roots are inactive.
Protective measures can be implemented for plants in exposed locations or those newly planted. Applying an anti-desiccant spray, a waxy, non-toxic coating, to the leaves in late fall helps reduce moisture loss from the foliage. For extreme conditions, physical barriers such as a temporary screen or burlap wrap can be erected around the shrub to diffuse strong winds and direct sunlight. While yellowing foliage can sometimes signal a nutrient deficiency, in winter it is often a sign of water stress or the onset of winter burn.