Yew trees, prized for their evergreen foliage and adaptability, are a popular choice in many landscapes. While generally robust, a common concern among owners is the unexpected yellowing of their needles. This article clarifies the various reasons why your yew might be displaying this discoloration and provides actionable steps to address and prevent it.
Reasons Your Yew is Turning Yellow
Imbalances in moisture, both overwatering and underwatering, are common causes. Saturated soil from overwatering deprives roots of oxygen, leading to root rot and yellowing. Conversely, underwatering or drought limits moisture and nutrient uptake, causing desiccation and pale foliage.
Extreme temperatures, such as winter cold with dry winds, can cause winter burn. Excessive summer heat or intense sun can also scorch needles, turning them yellow or bronze.
Nutrient deficiencies can manifest as yellowing foliage. A lack of nitrogen often causes pale yellowing of older needles. Iron deficiency, common in alkaline soils, typically results in interveinal chlorosis (yellow tissue, green veins). Magnesium deficiency presents similarly.
Pest infestations can lead to yellowing. Spider mites cause a stippled, yellowish appearance, often with fine webbing. Scale insects extract sap, resulting in localized yellowing and weakening.
Diseases, particularly root rot, can cause discoloration. Root rot, often due to waterlogged conditions, damages roots, preventing water and nutrient uptake and leading to widespread yellowing. Fungal needle blights can also cause specific areas of needles to yellow, brown, and drop.
Soil issues hinder root function and nutrient availability. Compacted soil restricts root growth and oxygen exchange, impairing absorption. Poor drainage creates waterlogging and root rot conditions. Incorrect soil pH locks up essential nutrients.
External chemical exposure can inflict damage. Herbicide drift can cause irregular yellowing patterns or deformities. Excessive de-icing salts can lead to salt accumulation, causing desiccation and yellowing.
Recent disturbances, like transplanting or physical damage, can trigger temporary yellowing. Transplant shock occurs when a newly planted yew struggles to establish. Physical damage to roots compromises water and nutrient absorption, causing foliage to yellow.
How to Diagnose Yellowing in Yews
Understanding the pattern and location of yellowing provides important diagnostic clues. Observe if discoloration affects new growth, older needles, specific branches, or the entire plant. Yellowing on older, inner needles suggests a different issue than on new growth tips.
Check soil moisture by inserting your finger two to three inches into the soil. Wet soil indicates overwatering; dry, crumbly soil suggests underwatering. A moisture meter offers precise readings.
Inspect the yew’s foliage and stems for pests and diseases. Examine needle undersides for spider mites or scale insects. Look for unusual spots, lesions, or fungal growth.
Consider recent events around the yew. Reflect on weather patterns, planting, or construction activities. Recall any nearby chemical applications like herbicides or de-icing salts.
Evaluate overall site conditions. Assess soil type (clay, sand, loam) and drainage. Note sun exposure, as insufficient or excessive light contributes to stress.
Solutions for Yellowing Yew Trees
Adjusting watering practices is often the most immediate solution. For overwatered yews, allow soil to dry between waterings and improve drainage. Underwatered yews need deep, consistent irrigation, especially during dry periods.
Address underlying soil issues. If soil pH is imbalanced, apply amendments like elemental sulfur (to lower pH) or lime (to raise pH), based on a soil test. Improve drainage in heavy clay soils by incorporating organic matter like compost, which also alleviates compaction.
For nutrient deficiencies, apply targeted fertilizers or soil amendments. If iron deficiency is suspected, use an iron chelate product. General deficiencies can be addressed with a balanced slow-release evergreen fertilizer, applied according to instructions.
Effective pest management involves identifying the specific pest and applying the correct treatment. Small spider mite infestations can be controlled with strong water streams; larger outbreaks may require horticultural oil or insecticidal soap. Scale insects can be hand-picked or treated with horticultural oil during their crawler stage.
Manage diseases by improving cultural conditions. For root rot, improve soil drainage and reduce watering frequency. Prune severely affected branches to prevent disease spread and improve air circulation.
Protect yews from environmental extremes. Apply organic mulch to regulate soil temperature and moisture. In harsh winter climates, anti-desiccant sprays reduce moisture loss, and burlap screens shield plants from wind and sun scald.
If chemical damage is suspected, immediate action can lessen the impact. If herbicide drift is recent, flush the soil with clean water. Prune severely damaged branches back to healthy wood to encourage new growth.
Preventing Yellowing in Yews
Proper planting techniques establish a strong foundation. Select a site with well-drained soil and appropriate sunlight (partial to full sun). Ensure the planting hole is wide enough and the tree is planted at nursery depth.
Establish a consistent watering schedule tailored to climate and soil. Monitor rainfall and adjust irrigation, ensuring adequate moisture during dry spells but allowing soil to dry slightly between waterings. Deep, infrequent watering is generally more beneficial.
Balanced fertilization, guided by soil test results, ensures necessary nutrients without excess. Yews do not require heavy fertilization; a light application of slow-release evergreen granular fertilizer in early spring can support growth if deficiencies are indicated. Avoid over-fertilizing, which can burn roots and cause yellowing.
Regular inspection allows for early detection. Routinely check needles, stems, and soil for discoloration, pest activity, or unusual growth. Addressing minor issues promptly prevents escalation.
Proper pruning contributes to vigor and air circulation, reducing disease risk. Remove dead, damaged, or diseased branches. Pruning to maintain an open canopy allows better air movement, preventing fungal issues.
Provide winter protection in colder climates to safeguard yews from desiccation and cold damage. Apply mulch around the base to insulate roots. Anti-desiccant sprays reduce moisture loss, and burlap can offer additional protection for young or exposed plants.
Be mindful of chemical applications near yews to prevent accidental damage. Exercise caution with herbicides on nearby lawns, choosing low-drift formulations and applying on calm days. Avoid excessive de-icing salts on adjacent walkways, or opt for less harmful alternatives.