Boxwoods often suffer winter injury when exposed to harsh winds, fluctuating temperatures, or prolonged periods of frozen ground that prevent water absorption. This damage typically manifests as bronzing, browning, or a straw-colored desiccation of the foliage, commonly known as winter burn. Most boxwoods are resilient and can be restored to their dense structure with calculated pruning and proper aftercare. This guide provides a plan to assess damage and effectively prune your shrubs for recovery.
Identifying the Extent of Winter Damage
Accurately diagnosing the depth of the injury is the first step toward successful recovery. Superficial leaf burn, where the foliage is discolored but the underlying wood is alive, will often shed naturally as the plant grows new leaves in the spring. This type of damage typically requires minimal intervention beyond waiting for new growth to emerge.
More severe damage, such as bark splitting or stem dieback, indicates that the vascular tissue has been compromised by extreme cold. To confirm which parts are truly dead, delay any major trimming until the plant has fully broken dormancy and begun its spring growth flush. This wait allows the plant to show exactly where the life remains.
The scratch test assesses the viability of the wood. Use a fingernail or a small knife to gently scrape away a tiny section of the outermost bark. If the tissue immediately underneath, known as the cambium layer, is bright green and moist, the branch is alive and has a good chance of recovering. Conversely, if the tissue is brown, tan, or dry, that section of the stem is dead and needs to be removed.
Optimal Timing and Tool Preparation
Pruning should be performed in the late spring or early summer, after the boxwood has clearly flushed new growth and the threat of a hard frost has passed. Waiting until this time ensures that all dead wood has been clearly identified, allowing for precise cuts that remove only the non-viable material. Pruning too early risks cutting back wood that may have still been alive, while pruning too late in the summer can stimulate tender new growth that will not harden off before the following winter.
Properly preparing your equipment is important for the pruning process. You will need sharp, handheld bypass pruners for smaller branches and loppers for thicker stems. Sharp tools create clean cuts that heal quickly, limiting the plant’s exposure to pathogens.
Before making any cuts, clean and sanitize your tools to prevent disease transmission. Wiping the blades with a disinfectant, such as rubbing alcohol or a mild bleach solution, before moving to the next plant is a sensible precaution.
Step-by-Step Guide to Removing Damaged Material
Begin the pruning process by removing all branches confirmed dead by the scratch test. Trace these dead stems back to a point where you find green, living tissue, or back to the main trunk or a larger branch. Make the cut just beyond a healthy bud or a lateral branch that is facing outward.
For plants with scattered dieback, focus on making thinning cuts rather than simply shearing the surface. Thinning involves reaching deep inside the shrub and removing small, damaged branches entirely. This technique allows sunlight to reach the inner canopy and promotes air circulation.
Avoid the temptation to use hedge shears to give the plant an immediate, uniform shape after a severe winter. Shearing only cuts the outer layer of foliage, which encourages dense growth on the surface while leaving a bare interior that is more prone to future winter injury. If large sections of the plant are dead, you may need to perform a heavier reduction, but you should not remove more than one-third of the total plant mass in a single season to prevent excessive shock. In cases of extreme damage, the shrub may appear misshapen immediately after pruning, but the healthy remaining stems will channel energy into new growth over the coming season.
Encouraging Regrowth and Future Protection
After pruning, the boxwood requires consistent care to support its recovery and stimulate new growth. Ensure the plant receives adequate water, especially during dry periods in the spring and summer. A deep, thorough watering once a week, rather than shallow daily sprinklings, encourages the development of a robust root system.
Apply a slow-release, balanced fertilizer in early spring or immediately following the pruning. This application supports new shoot development, but refrain from fertilizing after mid-summer, as late-season feeding can promote soft, tender growth that is highly susceptible to the next winter’s cold.
Proactive measures in the fall can significantly reduce the likelihood of repeated winter damage. Deeply water the shrub in late autumn, continuing until the ground freezes solid. This ensures the foliage is fully hydrated, helping to mitigate desiccation from winter winds.
Apply a two- to three-inch layer of organic mulch, such as shredded bark or wood chips, over the root zone after the ground has frozen. This mulch layer insulates the shallow roots and helps to conserve soil moisture, but it must be kept a few inches away from the trunk to prevent moisture buildup and rot. In exposed locations, consider installing a temporary windbreak or loosely wrapping the shrub in breathable burlap to shield it from harsh winter sun and drying winds.