Why Leaves Turn Yellow in Summer and How to Help
Chlorosis in Trees:
Why Leaves Turn Yellow in Summer and How to Help
August 4, 2026
As summer reaches its peak, you might notice an unexpected change in your yard: yellow leaves on trees that are usually vibrant and green. While autumn brings about natural color changes, yellowing leaves during the growing season can be a sign of trouble. One of the most common causes is a condition called chlorosis.
What Is Chlorosis?
Chlorosis is the yellowing of leaves due to insufficient chlorophyll—the pigment responsible for a leaf’s green color and a tree’s ability to convert sunlight into energy. When a tree can’t produce enough chlorophyll, its leaves lose their healthy green hue and turn yellow or pale green.
Common Causes of Chlorosis
- Very wet weather, poor drainage, or other non-living stress factors.
- Heavy, compacted, or alkaline soil (high pH)
- Root damage from construction or soil disturbance
- Species susceptibility—white oak, red maple, pin oak, river birch, paper birch, and white pine are especially prone
Why Does Chlorosis Matter?
Chlorosis isn’t just a cosmetic issue. When trees can’t access the nutrients they need, their overall health declines. Leaves may become stunted, pests and diseases can strike more easily, and trees may drop their leaves early. Over time, chronic chlorosis can shorten a tree’s lifespan.
How to Identify Chlorosis
Look for these symptoms:
- Leaves turning yellow but veins remain green (especially in maples)
- Yellowing starting on newer leaves or on one section of the tree
- Poor growth or thinning canopy
What to Do if You Suspect Chlorosis
If your tree is showing signs of chlorosis, it’s important to act quickly. The best first step is to contact an ISA Certified Arborist for a complete evaluation. They can diagnose the problem by inspecting your tree and testing your soil’s pH and mineral content.
Treatment and Prevention
Treatment depends on the cause and severity of chlorosis. Options may include:
- Applying mineral applications (iron or manganese) to the soil or directly to the tree
- Adding organic mulch to improve soil structure and lower pH
- Improving drainage or alleviating soil compaction
- Using growth regulators to encourage healthy root development
Preventive tips:
Treatment depends on the cause and severity of chlorosis. Options may include:
- Test your soil before planting new trees; avoid sensitive species if your pH is above 7.0
- Use organic mulch instead of rock or plastic liners
- Avoid using lime or limestone mulch near trees
Long-Term Outlook
Chlorosis can be persistent and may require repeated treatments over several seasons. Some trees recover fully, while others may need ongoing care or, in severe cases, replacement with a more tolerant species. Yellow leaves in summer are a warning sign that shouldn’t be ignored. Early diagnosis and treatment can restore your tree’s health and beauty, and proactive care can prevent chlorosis from recurring. If you see symptoms of chlorosis, reach out to a tree care professional for expert guidance and solutions.
FAQ:
Professional soil or foliar mineral applications, most often iron, give the quickest results because they work around poor nutrient absorption. Lasting recovery still depends on fixing the underlying cause, so an arborist usually pairs treatment with soil and drainage improvements.
No. Chlorosis is not a disease and does not spread. It is a symptom of a nutrient problem, though multiple trees sharing the same poor soil conditions may show it at the same time.
Homeowners can help by improving drainage and using organic mulch, but accurate diagnosis and mineral treatments generally call for a professional. Soil pH and nutrient testing pinpoint the real cause, preventing waste on treatments that don’t match the underlying problem.
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