Arborvitae, a popular choice for privacy screens and landscape accents, can sometimes yellow. This discoloration indicates underlying issues, requiring understanding and intervention to restore the plant’s health.
Common Causes of Arborvitae Yellowing
Arborvitae yellowing stems from various environmental or biological factors. Understanding these causes is the first step toward addressing the problem.
Watering issues, both too little and too much, are frequent culprits. Underwatering leads to dehydration, causing foliage to yellow. Conversely, overwatering, especially in poorly draining soils, can suffocate roots, leading to root rot and yellowing.
Nutrient deficiencies also contribute to yellowing foliage. A lack of essential elements like magnesium or iron can disrupt chlorophyll production, resulting in a faded green or yellow appearance. Sometimes, even if nutrients are present in the soil, cold temperatures or excessive moisture can temporarily prevent the plant from absorbing them effectively.
Winter desiccation, also known as winter burn, occurs when cold winds, bright sun, and frozen ground cause arborvitae needles to lose moisture faster than the roots can absorb it. This moisture imbalance leads to yellowing or browning, particularly on the exposed sides of the plant. Salt spray from nearby roads can also contribute to this type of damage.
Pest infestations can also cause arborvitae to yellow. Spider mites, tiny arachnids that feed on plant sap, cause yellowish speckling or stippling on needles, often accompanied by fine webbing. Bagworms, which construct protective bags from needles, chew on the foliage, leading to yellowing or browning as they consume plant tissue. Scale insects, another sap-feeding pest, also cause needle yellowing.
Fungal diseases, such as Needle Cast and Tip Blight, can discolor needles. Needle Cast causes needles to yellow, then brown, and fall off, sometimes with black fungal growth. Tip Blight causes needles and shoots to become pale green or yellow.
Arborvitae naturally sheds some inner needles in late summer or early fall as part of its aging process. This natural drop results in yellowing of the innermost foliage and is not a sign of distress.
Diagnosing Why Your Arborvitae is Yellowing
Identifying the cause of yellowing requires careful observation. The discoloration’s pattern and location provide important clues.
Observe the yellowing pattern. Inner needle yellowing, especially in fall, may be natural shedding. Yellowing on outer foliage, specific branches, or progressing from the bottom up often suggests issues like overwatering or root rot. Uniform yellowing across the entire tree can indicate widespread problems like underwatering or nutrient deficiency.
Assess soil moisture and drainage. Insert your finger or a trowel a few inches into the soil. Dry soil suggests underwatering. Consistently soggy or waterlogged soil indicates poor drainage and potential root rot. Well-drained soil should feel moist but not saturated.
Inspect the plant for pests or diseases. Look for tiny insects, webbing, or unusual growths on needles and branches. Signs include fine webbing from spider mites, spindle-shaped bags from bagworms, or black spots and discolored patches from fungal diseases.
Consider environmental factors contributing to yellowing. Reflect on recent weather, such as prolonged dry spells or unusually cold winters. Evaluate the planting location for adequate sunlight; arborvitae thrive with at least six hours of direct light daily. Also, consider any recent landscape changes, like de-icing salts.
Solutions for Yellowing Arborvitae
Once the cause of yellowing is identified, specific actions can restore arborvitae health. Addressing the underlying problem is important for effective recovery.
Adjusting watering practices is often the first step. For underwatered plants, provide deep, thorough waterings. New arborvitae need consistent moisture, especially during their first two growing seasons, often requiring weekly soaks. For overwatered plants, allow the soil to dry out between waterings. Checking soil moisture by hand or with a moisture meter helps prevent both overwatering and underwatering.
Addressing nutrient deficiencies involves applying appropriate fertilizers or soil amendments. A balanced, slow-release fertilizer applied in early spring provides essential nutrients. If a specific deficiency like iron or magnesium is suspected, a targeted supplement may be beneficial, but avoid over-fertilization, which can stress the plant.
Protecting arborvitae from winter damage involves proactive measures. Water the plant well in fall before the ground freezes to prevent desiccation. Apply a thick layer of mulch around the base to insulate roots and retain moisture. In severe winters, wrapping plants in burlap shields them from harsh winds and snow. Anti-desiccant sprays can also reduce needle moisture loss.
Managing pests and diseases requires specific treatments. For spider mites, use a strong water stream or miticides for severe infestations. Hand-pick bagworms or cut them from the plant. Fungal diseases often benefit from pruning affected areas and improving air circulation; fungicides may also be used. If root rot is present due to poor drainage, improve soil aeration.
Pruning affected areas improves plant appearance and health. Remove yellowed, dead, or diseased branches using clean, sharp shears. This redirects energy to healthy growth and improves air circulation.
Preventing Future Arborvitae Yellowing
Establishing sound horticultural practices prevents future yellowing and maintains arborvitae health. Proactive measures help plants thrive and resist common stressors.
Proper planting sets the foundation for healthy growth. Arborvitae prefers well-drained soil and at least six hours of daily sunlight. Dig a hole twice as wide as the root ball but only as deep as the root ball, ensuring the top is level with or slightly above the soil line.
Consistent watering is important, especially for newly planted arborvitae, which require regular moisture for the first two growing seasons. Established plants need deep, infrequent watering, about one inch per week when rainfall is insufficient, to encourage deep root growth. Avoid frequent, shallow watering, as this promotes shallow root systems susceptible to drought stress.
Mulching offers multiple benefits. A 2-4 inch layer of organic mulch, such as shredded bark or pine fines, helps retain soil moisture, suppresses weed growth, and moderates soil temperature. Keep mulch a few inches away from the trunk to prevent moisture buildup and potential rot.
Regular inspection allows for early detection of problems. Periodically examine foliage for signs of discoloration, pest activity, or unusual growth. Early identification prevents issues from becoming severe, allowing timely intervention and maintaining the plant’s vibrant green appearance.