Leaves Turning Yellow: What's Causing It and How to Fix It Insects, Mites & Diseases Tree & Shrub Care Submitted by Elisa Edelstein Reviewed by Expert Patrick Parker, Director of Plant Health Care If you've noticed leaves turning yellow on a tree or shrub in your yard, you're not alone. It's one of the most common concerns homeowners bring to a certified arborist. Sometimes it's a normal part of a plant's seasonal cycle. Other times, it's an early signal that something below the surface needs attention. Understanding the difference can save a tree that's still salvageable, and it starts with knowing what to look for. Is It Normal for Leaves to Turn Yellow? Not all yellowing is cause for concern. Deciduous trees naturally shift color and drop leaves each fall as part of their dormancy cycle, and older, interior leaves on evergreens can yellow and shed as new growth takes over. Look at the pattern, as expected seasonal yellowing tends to be gradual, uniform, and tied to the calendar. Leaves turning yellow that appear suddenly, unevenly, or outside the normal season are more often a sign of stress and should be investigated before it spreads. The Most Common Reasons Leaves Turn Yellow Nutrient Deficiency: Not Enough Iron, Nitrogen, or Magnesium Chlorosis is the yellowing that occurs when a plant can't produce enough chlorophyll and is often traced to a shortage of key nutrients. Iron and magnesium deficiencies typically show up as yellowing between the leaf veins while the veins themselves stay green, while nitrogen deficiency tends to yellow the entire leaf, starting with older growth. The soil may have the nutrients the tree needs, but soil pH or compaction may lock them up, which is why targeted fertilization often works better than a generic feeding. Overwatering and Poor Soil Drainage Roots need oxygen as much as they need water. When soil stays saturated for too long, roots can't take up nutrients properly and begin to suffocate; yellowing leaves are often one of the first visible signs. Heavy clay soil, poor grading, or irrigation systems running too frequently are common culprits. Underwatering and Drought Stress On the other end of the spectrum, a tree that isn't getting enough water will often have leaves turn yellow and drop as a survival response, shedding foliage to reduce moisture loss. This is especially common in newly planted trees that haven't yet established a deep root system, or during extended summer dry spells. When Yellowing Leaves Signal a Bigger Tree Health Problem Fungal Disease and Leaf Spot Fungal pathogens like leaf spot or anthracnose often start as small yellow or brown spots that expand over time, sometimes merging into larger blotches before leaves drop early. Cool, wet spring weather often creates ideal conditions for these diseases to take hold. Insect Infestations That Cause Leaf Discoloration Pests that feed on leaves or sap, such as: Aphids Spider mites Scale Lace bugs, Can cause stippled or yellowed foliage well before other signs of infestation become obvious. Because the damage can look similar to nutrient or water stress at a glance, a closer inspection of the undersides of the leaves and along the branches is usually necessary to confirm the cause. Root Damage and Soil Compaction Construction activity, foot traffic, and heavy equipment can compact soil around a tree's root zone, restricting the oxygen and water flow that roots depend on. Root damage from digging, trenching, or grade changes can cause yellowing that appears months or years after the original disturbance, making the connection easy to miss. How to Diagnose Why Your Leaves Are Turning Yellow What to Look for Before Calling an Arborist Before scheduling a visit, it helps to note a few details, such as which leaves are affected (new growth or old, one side of the canopy or the whole tree), how quickly the leaves turned yellow, and whether you've noticed any recent changes nearby, such as new construction, altered irrigation, or recent storms. This context helps an arborist narrow down the likely cause faster. Why a Soil Test Can Reveal the Real Problem Because so many causes of leaf yellowing trace back to what's happening below ground, a soil test is often the fastest way to rule things in or out. It can reveal pH imbalances, nutrient shortages, and compaction issues that aren't visible from the surface, turning a guessing game into a targeted treatment plan. How to Fix Yellowing Leaves on Trees and Shrubs Adjusting Watering and Drainage If overwatering or poor drainage is the issue, adjusting irrigation schedules, improving soil aeration, or regrading around the root zone can relieve the stress that causes leaves to turn yellow. For drought-stressed trees, a consistent, deep watering schedule, rather than frequent shallow watering, helps rebuild resilience. Fertilization and Nutrient Treatments When a soil test confirms a nutrient gap, targeted fertilization can correct the imbalance more effectively than surface-level feeding. SavATree's ArborHealth® program and ArborKelp® treatments are designed to address deficiencies at the root level. Disease and Insect Treatment Options Fungal diseases and insect infestations each call for a different approach, from targeted fungicide applications timed to the pathogen's life cycle to integrated insect management strategies that treat infestations while protecting beneficial insects. Because misdiagnosing the cause can lead to ineffective treatment, a certified arborist's assessment often makes the most difference. Left untreated, the causes of leaves turning yellow compound. Nutrient deficiency weakens a tree's disease defenses, and disease stress worsens drought damage. Treating the root cause early is cheaper and more effective than waiting until it shows throughout the canopy. If you're seeing yellowing leaves on your trees or shrubs, an experienced SavATree ISA Certified Arborist can help pinpoint the cause and recommend the right treatment before it spreads. Contact us today to schedule a consultation with an expert arborist.