The Green Giant Arborvitae is chosen for rapid growth and dense privacy screens. While resilient, its foliage sometimes turns yellow, signaling an underlying issue. Addressing this discoloration restores the plant’s vibrant green.
Common Reasons for Yellowing
Green Giant Arborvitae can yellow due to natural processes, environmental stressors, pests, or diseases. Understanding these causes is the first step.
Natural Needle Shedding
Green Giant Arborvitae naturally sheds older, inner needles. This normal process causes inner needles to yellow and drop. This uniform yellowing of the inner canopy is not a concern.
Watering Issues
Both insufficient and excessive watering can cause yellowing. Underwatering leads to desiccation, turning needles yellow and brittle. Overwatering causes root rot from saturated soil, preventing nutrient absorption. Yellowing often starts at the base.
Nutrient Deficiencies
Specific soil nutrient deficiencies can cause yellowing. Nitrogen deficiency often causes general yellowing, starting on older, inner leaves. Insufficient iron or magnesium can lead to chlorosis, causing interveinal yellowing. Soil pH imbalances can hinder nutrient uptake.
Pests
Pests cause discoloration. Spider mites suck cell contents, yellowing needles often with fine webbing. Bagworms create cone-shaped bags, defoliating and yellowing branches. Scale insects feed on plant sap, causing yellowing foliage and sticky honeydew.
Diseases
Fungal diseases contribute to yellowing. Root rot, linked to wet soil, causes wilting, yellowing leaves, and branch dieback. Canker diseases result in sunken lesions on branches, causing yellow or brown foliage. Needle blights (Pestalotiopsis) cause needles to turn pale green or yellow before browning, with black spots.
Environmental Stress
Environmental stressors cause yellowing:
Winter burn: Cold winds and sun desiccate needles, causing yellowing or bronzing.
Heat stress and drought: Cause wilting and yellowing.
Transplant shock: In new trees, can cause temporary yellowing as the plant adjusts.
Salt damage: From de-icing salts or coastal spray, can burn roots and foliage, causing yellowing.
Diagnosing the Problem
To identify the cause of yellowing, examine the plant and its environment. Observe the yellowing pattern and location: inner needle yellowing suggests natural shedding, while outer tips or new growth points to other issues. Assess soil moisture by feeling a few inches deep; saturated soil indicates overwatering/root rot, dry soil points to underwatering. Inspect foliage for pests (spider mites, bagworms, scale insects) and disease symptoms (cankers, wilting, unusual spots).
Consider recent environmental factors like extreme weather (heat, cold, wind, drought). Recall recent activities like planting, fertilizing, or construction. Check for proper planting depth; too deep can cause stress.
Effective Solutions for Yellowing
Once the cause of yellowing is identified, targeted solutions restore health. Adjust watering: provide deep, consistent irrigation for underwatered plants (moist but not waterlogged); for overwatered plants, allow soil to dry and improve drainage. Address nutrient deficiencies by applying a balanced, slow-release evergreen fertilizer; a soil test confirms imbalances and guides fertilizer choice. For pests, horticultural oils or insecticidal soaps manage spider mites and scale; hand-pick small bagworm infestations, or use biological/targeted insecticides for severe issues.
Disease management focuses on improving growing conditions. For root rot, improve soil drainage; fungicides may be applied. Prune and remove infected branches (cankers, blights), sterilizing tools to prevent spread. Mitigate environmental stress with winter protection, mulching for temperature/moisture regulation, and proper planting depth to minimize transplant shock.
Preventing Yellowing and Promoting Health
Proactive measures and consistent care prevent yellowing and promote long-term health. Consistent, proper watering is important, particularly during dry periods and establishment. Aim for deep waterings for robust root development, not shallow applications.
Apply organic mulch around the base of trees to retain soil moisture, regulate temperature, and suppress weeds.
Regular annual fertilization with a balanced evergreen formula in early spring replenishes nutrients, promoting vigorous growth and vibrant foliage.
Ensure correct planting depth and spacing for good air circulation and reduced competition. Regularly inspect for early signs of pests, diseases, or environmental stress for prompt intervention.