What causes hydrangea leaves to turn yellow?
Written by
Michael Sullivan
Reviewed by
Prof. Martin Thorne, Ph.D.Yellowing leaves on hydrangea can be a concern for gardeners, indicating potential health problems that require action. In many cases, yellowing is related to imbalanced soil, poor watering patterns, or a lack of nutrients, rather than disease. Determining the exact reason for leaf yellowing requires examining the leaf pattern and testing the soil conditions. I experienced a complete recovery of my own hydrangeas with the treatment of iron deficiency.
Soil pH Imbalance
- Alkaline soils above pH 7.0 lock out iron causing interveinal yellowing
- Test soil pH annually using reliable kits from garden centers
- Apply elemental sulfur to lower pH or chelated iron for immediate correction
Nutrient Deficiencies
- Iron deficiency shows as yellow leaves with green veins (chlorosis)
- Nitrogen shortage causes uniform yellowing starting on older leaves
- Apply balanced fertilizer with micronutrients every 4-6 weeks during growing season
Watering Issues
- Overwatering causes yellowing and leaf drop with constantly wet soil
- Underwatering creates crispy brown edges with yellowing between veins
- Check soil moisture 4 inches deep and water only when dry at this level
Environmental Stress
- Excessive sun scorches leaves causing yellow/brown patches
- Root damage from freezing temperatures shows as sudden yellowing
- Apply 3-inch mulch layer and provide afternoon shade in hot climates
Soil testing yields valuable information on possible treatment measures before application of treatments. Samples should be taken from the root zone of the plant at approximately 6-8 inches. Soil testing will indicate the soil's pH levels and nutrient deficiencies that may contribute to yellowing. For alkaline soils, apply elemental sulfur at a rate of one cup per plant, while acidic soils may require lime adjustments. I test my hydrangea beds every spring.
Nutrient correction calls for a precise fix. A plant that is iron-deficient will respond quickly to a foliar spray of chelated iron, as is the case with many other nutrients. A nitrogen deficiency will need to be treated with a slow-release fertilizer applied to moist soil. It is then necessary to water the fertilizer consistently to prevent root burn. My hydrangeas went from dead and brown to green within two weeks of using iron.
Water use decreases stress-induced yellowing. It is a good idea to add compost to clay soils to improve drainage as well. Organic matter should be added to sandy soils to improve water retention. Use drip irrigation, so the leaves stay dry, allowing for a more consistent moisture regime. Container plants require additional attention to ensure drain holes remain open.
Environmental alterations protect against yellowing. In summer months, provide shade in the afternoon, which is especially useful in zones 7-9. In cold areas, apply mulch in the winter, before the first frost. Do not plant near concrete, as this can cause alkalinity to leach. My hydrangeas, planted near foundations, required extra acidification to maintain their green color.
Read the full article: How to Care for Hydrangea: Complete Growing Guide
