Boxwood shrubs are a popular evergreen choice, valued for their dense, fine-textured foliage that provides structure and color to landscapes year-round. The direct answer to whether they stay green all year is yes, as they are botanically classified as broadleaf evergreens. They retain their leaves through all seasons, making them highly desirable for formal gardens and hedges. However, the common sight of brown or yellowing boxwoods in winter often leads gardeners to question this evergreen promise.
The Evergreen Nature of Boxwoods
Boxwoods belong to the genus Buxus, and their evergreen status is rooted in their specialized leaf structure. Unlike deciduous plants, which shed their leaves to conserve water, boxwoods keep their foliage. Their small, oval-shaped leaves have a tough outer layer called a waxy cuticle, which is designed to minimize water loss, or transpiration, during the colder months.
These leaves continue to perform a reduced amount of photosynthesis even when temperatures drop, allowing the plant to sustain itself slowly through winter. The dense arrangement of the foliage also helps to insulate the inner branches, protecting the plant from environmental extremes. This combination of physical and functional adaptations allows boxwoods to maintain their green appearance throughout the year.
Why Boxwoods Lose Their Green Color in Winter
Despite their evergreen adaptations, boxwoods are highly susceptible to discoloration during the winter. The most common cause is winter burn, a condition that occurs when the leaves lose moisture faster than the roots can replace it. This desiccation happens because winter wind and sun cause the foliage to release water vapor, but the water in the frozen soil is inaccessible to the roots. The damaged foliage often appears dried out, brown, or straw-colored, typically on the side of the shrub facing the prevailing wind or winter sun.
Cold Bronzing
Another form of discoloration is cold bronzing, a less severe and often temporary physiological response. The green chlorophyll pigment in the leaves begins to break down or its production slows due to cold temperatures and intense sun exposure. This reduction allows underlying pigments, such as purple or orange anthocyanins, to become visible, giving the foliage a reddish-brown or bronze hue. Bronzing is not a sign of death and usually reverts to green once warmer weather returns in the spring.
Chlorosis (Nutritional Deficiency)
Discoloration can also signal a nutritional problem, such as chlorosis, which presents as a generalized yellowing of the leaves. Boxwoods prefer a nearly neutral soil pH. If the soil becomes too acidic, essential micronutrients like iron and magnesium can become unavailable. This deficiency prevents the shrub from producing enough chlorophyll, resulting in a pale green or yellow appearance.
Strategies for Maintaining Vibrant Green Foliage
The primary strategy for keeping boxwoods green is to focus on moisture retention and protection from harsh winter elements.
Moisture Management
Deep watering in the late fall is the most effective preventative measure against desiccation and winter burn. Saturating the soil before the ground freezes provides the plant with a reservoir of moisture, helping to balance the water lost through the leaves during dry, windy periods.
Applying a two- to three-inch layer of organic mulch around the base of the shrub helps to insulate the shallow root system. This protective layer moderates soil temperature fluctuations and helps the soil retain moisture for longer.
Protection from Elements
Proper placement and wind protection are important, especially in colder climates. Boxwoods should be sited away from areas that receive direct, intense winter sun and strong, drying winds, such as south or west exposures. If a shrub is in an exposed location, installing a temporary windbreak, such as burlap screens or stakes, can reduce the desiccating effect of the wind. Ensure that any material used is breathable to prevent moisture build-up and subsequent fungal issues.
Gardeners can also apply an anti-desiccant spray to the foliage in late fall and mid-winter. This spray creates a waxy film over the leaves, which reduces the rate of water evaporation and offers another defense against winter burn.