Arborvitae (Thuja) are popular evergreen trees valued for their dense, often columnar foliage that provides year-round privacy and structure. While generally hardy, winter presents unique challenges that can lead to significant damage if they are left unprotected. Primary threats include desiccation (winter burn) from moisture loss, structural damage from heavy snow and ice, and feeding pressure from browsing wildlife. Implementing specific protective measures ensures these plants remain healthy and vibrant until spring.
Essential Hydration and Soil Preparation
Preparing the root zone in the fall is a foundational step to preventing winter dehydration. Evergreens lose water through their foliage even when dormant, but frozen ground prevents water replacement. This lack of water uptake is the main cause of winter burn.
Establish a deep watering regimen in late fall, continuing until the soil freezes solid. Saturate the root ball thoroughly to provide a reservoir of moisture the plant can draw upon before the water becomes inaccessible. Slow, deep watering encourages maximum water storage, which is especially important following a dry autumn.
Applying a 2- to 3-inch layer of organic mulch helps regulate soil temperature and moisture. Spread shredded bark or wood chips across the root zone to insulate the ground, slowing the rate at which the soil freezes and thaws. This consistent temperature helps prevent frost heave, a condition where alternating freezing and melting cycles damage delicate roots. Keep the mulch several inches away from the trunk to prevent moisture buildup and potential disease.
Mitigating Winter Burn and Wind Stress
Winter burn occurs when sun and wind draw moisture from the foliage faster than the plant can replenish it from frozen roots, leading to browning and scorching. Damage is often concentrated on sides facing prevailing winter winds or intense sun, typically south and southwest exposures. This scorched, dried-out appearance takes considerable time to repair in the spring.
Applying an anti-desiccant spray offers defense against moisture loss. These products create a thin, waxy coating on the foliage, slowing transpiration (water loss) by 15% to 20%. Apply in late fall when temperatures are mild (40 to 50 degrees Fahrenheit) and before the ground is permanently frozen. If applied too late or when temperatures are too cold, the spray may not dry properly, risking cellular damage from trapped moisture.
For plants in highly exposed locations, construct a temporary windbreak against drying winds. Secure a barrier of burlap or shade cloth to stakes driven a few feet away from the arborvitae. Place this screen on the windward side to deflect air currents while still allowing circulation. This physical shield minimizes evaporative stress and prevents rapid browning.
Physical Defense Against Snow Load and Wildlife
The structural integrity of columnar arborvitae, such as ‘Emerald Green,’ is often compromised by heavy, wet snow and ice. The dense, multi-stemmed structure easily collects snow, causing branches to splay outward or break entirely, resulting in permanent deformation. To prevent this structural damage, gently bundle the branches together before the first heavy snowfall.
Achieve bundling by spiraling a flexible material, such as soft jute twine or coated wire, around the plant from the base upward. The twine must be snug enough to hold the branches in a compact column but not so tight that it restricts growth or cuts the foliage. If heavy snow accumulates, remove it carefully using a broom to lightly brush the snow upward. Never shake frozen branches, as this causes them to snap under stress.
Arborvitae are a preferred food source for deer and rabbits, especially when natural forage is scarce. The most effective defense against animal browsing is a physical exclusion barrier. Install a cage or temporary fence made of plastic netting or welded wire around individual plants.
The structure must be tall enough to deter deer, often requiring 8 feet of height, especially if snow depth increases the ground level. Place the barrier approximately 6 inches away from the outer branches to prevent animals from reaching the foliage. When springtime arrives, promptly remove all twine and temporary barriers to allow normal growth and prevent girdling or bark damage.