Boxwoods, belonging to the Buxus species, are valued evergreen shrubs that provide structure and deep green color to landscapes throughout the year. Their broadleaf evergreen nature makes them particularly susceptible to damage during the winter months. The primary threat is desiccation, or winter burn, which occurs when the leaves lose moisture faster than the frozen roots can replace it. This leads to the characteristic bronzing and browning of the foliage. Preparing these shrubs involves a series of proactive steps to ensure they enter dormancy well-hydrated and protected from environmental extremes.
Foundational Steps for Winter Readiness
Preparation for winter begins long before the first frost, specifically during the late summer and early fall months. The most important step is to stop applying high-nitrogen fertilizers by mid-to-late summer. These products encourage new, tender growth that cannot harden off before cold temperatures arrive. Instead, applying a phosphorus-rich fertilizer in the early fall can stimulate root development and improve the plant’s overall cold hardiness.
Pruning should be completed well in advance of the first expected hard freeze, typically no later than six weeks prior. This allows new cuts to heal and prevents a flush of vulnerable growth. The most crucial preparatory action is deep watering, which must be completed before the ground freezes solid. Boxwoods have shallow root systems, so thoroughly soaking the soil ensures the plant has maximum moisture reserves to draw upon throughout the winter.
Mitigating Moisture Loss and Winter Desiccation
Once boxwoods are adequately hydrated, the next focus shifts to reducing the rate of moisture loss from the leaves, which is known as transpiration. Anti-desiccant sprays, also called anti-transpirants, are polymer-based products that create a thin, waxy coating on the foliage to slow water evaporation. This protective layer can reduce moisture loss by approximately 15 to 20 percent, directly combating the effects of drying winter winds.
The timing and conditions for application are specific: the spray should be applied in late fall or early winter after the plant is dormant but before temperatures consistently drop below 40°F. Apply the anti-desiccant on a clear, dry day when temperatures are above freezing, ideally between 40°F and 50°F, ensuring the coating adheres and dries properly. Since the coating gradually breaks down, a second application in mid-to-late winter may be necessary for prolonged protection.
It is important to monitor soil conditions during winter warm spells, especially if the ground thaws. If the soil is dry and the air temperature is above 40°F, a supplemental mid-day watering can help rehydrate the plant. This allows the roots to take up moisture before the ground potentially refreezes at night. This rehydration is important because the greatest risk of desiccation occurs in late winter when the stored moisture reserves have been depleted.
Installing Physical Barriers Against Wind and Sun
While anti-desiccant sprays address moisture loss, physical barriers are often the best solution for protecting boxwoods from mechanical damage and environmental extremes like sun scald and windburn. Burlap is the preferred material for creating these shields because its woven structure allows for air circulation. This prevents the buildup of moisture and heat that can encourage fungal issues.
Instead of tightly wrapping the entire shrub, install a windbreak screen on the side facing the prevailing winter wind or intense afternoon sun. This barrier can be constructed by driving stakes into the ground and stretching burlap tightly between them to create a fence-like enclosure. Avoid using plastic materials, which trap heat and moisture, leading to condensation and potentially scalding the foliage when the sun hits it.
Physical barriers also protect the foliage from abrasive road salt spray, which can compound desiccation stress, making them useful for shrubs near driveways or walkways. For tall or upright boxwoods, a loose wrap of burlap or twine can be used to gently tie the branches inward. This helps prevent breakage from heavy snow and ice loads.
Root Zone Insulation and Spring Thaw Preparation
Protecting the shallow root system of the boxwood from fluctuating temperatures is accomplished through the use of mulch. A layer of organic mulch, such as shredded bark or pine needles, should be applied 2 to 4 inches deep and extend to the dripline of the shrub. This insulation stabilizes soil temperature and prevents the destructive freeze-thaw cycles that can cause frost heaving, where the roots are lifted and exposed.
It is important to keep the mulch several inches away from the base of the shrub’s trunk to prevent moisture retention against the crown, which can lead to disease and rot. During periods of heavy snowfall, gently brush excess snow off the branches with a broom, moving upward. This prevents the limbs from splaying or snapping under the weight. Avoid piling snow from walkways onto the shrubs, as this introduces high salt concentrations and excessive weight.
The spring transition requires patience, as removing protective barriers too early can expose the plant to late-season sun scald and wind damage. Burlap wraps and screens should be removed slowly, ideally on an overcast day to allow the foliage to reacclimate gradually to full sun exposure. Once the ground has fully thawed and new growth begins to appear, regular watering should resume to ensure a healthy recovery from the winter dormancy.