Boxwood Winter Burn vs Blight – How to Tell the Difference and Prevent Damage

Boxwood shrubs are a classic landscaping plant, valued for their versatility, deer resistance, and year-round interest. However, boxwood is prone to two common problems that can quickly damage or even kill plants – winter burn and blight. Learning how to distinguish between and prevent these issues is key to keeping your boxwood healthy.

What Causes Boxwood Winter Burn?

Boxwood winter burn occurs when foliage is damaged by harsh winter winds, extreme cold, winter sunscald, or a combination of factors. Evergreen leaves continue to lose moisture during the winter months through transpiration. Under normal conditions, the roots replace this lost moisture. But if the ground is frozen or plants are exposed to drying winds, the foliage cannot take up enough water to replace what is lost and literally dries out or burns.

Symptoms of winter burn in boxwood include:

• Tan, brown, or black foliage, typically only on exposed portions of the plant. This often appears as a distinct line or “snowline” where protected foliage remains green.

• Damage only shows up on the plants’ edges or on the sides that face the prevailing winds. The inner branches are usually safe.

• Burned foliage drops off leaving bare stems.

• Most of the time, damage is worst after a winter with little snow cover, periods of extreme cold and warmth with sunny days and freezing nights, or exposure to winter winds.

What Causes Boxwood Blight?

Boxwood blight is a fungal disease that can quickly kill and remove the leaves from boxwoods. This very contagious disease spreads rapidly during cool, moist conditions. Boxwood blight can happen at any time when it’s cool and damp, but it happens most often in the spring and fall.

Symptoms of boxwood blight include:

• Dark or light brown circular leaf spots with dark borders.

• Black streaks on stems.

• Rapid defoliation, leaving bare stems.

• Entire plants turning brown or straw-colored.

• Rapid plant decline and death, especially on young plants.

• Defoliation and dieback continues to progress on plants until the entire shrub is affected.

• Infected leaves and stems have a distinct musty odor.

How to Tell the Difference

While both boxwood blight and winter burn can cause similar leaf browning and defoliation, there are some key differences to look for:

Winter Burn:

• Damage only on exposed outer portions or one side of plant
• Distinct snowline between damaged and healthy foliage
• Worst on outer branches, inner protected branches remain green
• Tan, burnt appearance to damaged leaves
• Total extent of damage apparent once weather warms in spring
• No musty odor

Boxwood Blight:

• Entire plant becomes infected, not just outer portions
• Leaves brown from the bottom up or randomly over plant
• Defoliation and dieback spreads continuously
• Dark brown leaf spots with black borders
• Black stems
• Rapid defoliation in cool, moist weather
• Musty odor to infected plant parts

How to Prevent Boxwood Winter Burn

While we can’t control the weather, there are a few things you can do to help prevent winter damage on boxwoods:

• Provide wind protection. Site boxwoods in a location shielded from harsh winter winds, such as against a wall or building on the north or west side of your home. Planting on the south side of the home can actually increase damage by allowing the winter sun to warm plants, leading to moisture loss.

• Avoid full winter sun. Boxwoods prefer partial shade, especially in winter. Plants that are in full sun and have frozen soil have a hard time getting enough water to replace what they lose through transpiration.

• Insulate roots. Apply 2-3 inches of shredded bark mulch around plants to keep roots warmer and prevent soil from freezing.

• Water in fall. Deep watering before the ground freezes helps boxwoods go into winter well-hydrated.

• Cover plants. Burlap screens or fabric wraps protect foliage from drying winds and sun. Avoid plastic wraps that can actually cause more damage.

• Prune for shape and air flow. Maintain a shapely form by removing interior branches and any damaged wood. Allow good air circulation through plants.

• Choose wind-tolerant varieties. Pick more hardy cultivars like Wintergreen, Winter Gem, or Glencoe.

How to Prevent Boxwood Blight

Preventing boxwood blight involves utilizing cultural practices to keep plants healthy and avoiding introducing the disease:

• Inspect plants. Examine boxwoods for signs of infection like leaf spots and rapid defoliation. At first signs, begin treatment.

• Isolate infected plants. Remove and destroy plants with boxwood blight to avoid it spreading.

• Practice sanitation. Sterilize pruners between plants to avoid transmitting disease. Rake and remove all fallen leaves.

• Improve air circulation. Allow good spacing between plants and prune to open up interior branches.

• Water in early morning. Avoid overhead irrigation and water at the soil line to keep foliage dry.

• Apply fungicides. Protective fungicides may help prevent infection in areas where blight is active.

• Purchase from reputable nurseries. Ask if their stock is certified disease-free. Avoid boxwoods from unknown sources.

Protect Your Boxwood Investment

Boxwood shrubs have been prized landscape plants for centuries, but they do require proper siting and care. By recognizing the difference between boxwood winter burn and blight, and utilizing preventative practices, you can help keep your boxwood looking healthy for years to come. With a little TLC, the classic boxwood will continue gracing gardens for generations more.