The Green Giant Arborvitae (Thuja ‘Green Giant’) is a popular evergreen, prized for its rapid growth and dense, pyramidal form, making it ideal for privacy screens and windbreaks. While generally robust and low-maintenance, it can face specific issues affecting its health. Understanding these common problems helps homeowners identify and address them, ensuring the trees’ long-term vitality.
Environmental Stress Issues
Green Giant Arborvitae can show distress from environmental factors. Both overwatering and underwatering cause problems. Overwatering leads to root rot, yellowing foliage, and drooping branches as roots lack oxygen in soggy soil. Conversely, underwatering causes browning tips and dull foliage, indicating insufficient moisture, especially during dry spells or establishment. Newly planted trees need consistent moisture, about one inch every week to ten days, until fully established (at least a year).
Winter burn, or desiccation, affects evergreens like Green Giants in colder months. This happens when cold, dry winds and frozen ground prevent water absorption, leading to browning and dieback, particularly on exposed sides. To prevent winter burn, water trees well in fall before ground freeze, and consider anti-desiccant sprays or burlap wraps as windbreaks. Extreme heat or sun exposure, especially for young or newly transplanted trees, can also cause stress, leading to browning leaves and stunted growth.
Pest Infestation Problems
Green Giant Arborvitae are generally pest-resistant, but some insects cause damage. Spider mites cause stippled or discolored foliage, often with fine webbing. Infestations lead to browning and decline, especially in hot, dry conditions. A strong water stream can dislodge mites, while insecticidal soaps or horticultural oils offer control.
Bagworms are identified by distinctive, spindle-shaped cocoons hanging from branches. Their larvae feed on foliage, causing defoliation and weakening the tree. Hand-picking and destroying bags before larvae hatch in late spring is effective. For larger infestations, apply insecticide when larvae are small and actively feeding. Scale insects appear as small, stationary bumps on stems and foliage, drawing sap and causing yellowing and stunted growth. Horticultural oil applications can smother these pests, managing populations.
Disease Challenges
Green Giant Arborvitae can face disease challenges, especially with unfavorable environmental conditions. Cercospora needle blight, a fungal disease, browns inner needles, progressing outwards and upwards. Improving air circulation and pruning affected branches helps manage it; fungicides are an option for severe cases. Phytophthora root rot is a common, often fatal fungal disease from poor soil drainage or overwatering. Symptoms include wilting, yellowing foliage, and eventual plant death as roots decay. Preventing this disease requires proper site selection with well-draining soil and avoiding overwatering.
Other blights, like tip blight, can also affect Green Giants, causing browning and dieback of branch tips. Canker diseases, identifiable by sunken lesions on branches, occur in shaded areas or where bark stays moist. Promptly removing affected branches and ensuring the plant is not overly stressed helps mitigate fungal spread.
Animal Damage
Wildlife can damage Green Giant Arborvitae, especially when other food sources are scarce. Deer browsing is a widespread problem, particularly in winter, as deer chew or tear foliage, causing noticeable damage and stunted growth. While Green Giants are more deer-resistant than some arborvitae varieties, they are not entirely deer-proof, especially when hungry. Deterrents like commercial repellents or physical barriers such as fencing can protect trees from browsing.
Other animals also cause damage. Rabbits may gnaw on young tree bark, which can girdle the trunk and severely harm the plant. Voles, small rodents, damage roots by tunneling underground, leading to plant decline. Protecting the base of young trees with tree guards or hardware cloth offers defense against these smaller pests.
Promoting Long-Term Health
Ensuring Green Giant Arborvitae’s long-term health starts with proper planting. Dig a hole twice as wide as the root ball but only as deep, allowing roots to spread without being planted too deeply. Proper spacing, typically 5 to 6 feet apart for a privacy hedge, ensures good air circulation and prevents overcrowding as trees mature.
Apply a 3 to 6-inch layer of organic mulch around the tree’s base to retain soil moisture, regulate temperature, and suppress weeds. Keep mulch a few inches from the trunk to prevent moisture buildup and rot. Green Giants generally require little pruning, but removing dead, diseased, or damaged branches benefits vigor and improves air circulation. Pruning can also maintain height or shape, ideally in late winter before new growth. Fertilization is often unnecessary for established Green Giants, but young trees benefit from a balanced, slow-release evergreen fertilizer in early spring for vigorous growth. Regular monitoring for early signs of stress, pests, or disease allows timely intervention, contributing to the trees’ overall resilience and health.