Your hydrangea leaves yellow from four main causes. Too much water, iron lockout, nitrogen shortage, or just natural aging. Each problem shows a different pattern on the leaves. Learn to read these signs and you can fix the issue before it spreads.
I once helped a friend solve a mystery with her hydrangea planted near a foundation wall. The leaves turned yellow between the veins while the veins stayed green. This is iron chlorosis at work. The concrete had leached lime into the soil for years. This pushed the pH so high that iron became locked away from the roots. Even though iron was in the soil, the plant couldn't use it.
A different garden gave me another lesson. My own hydrangea near the back fence showed uniform pale yellow across all leaves. No pattern, just overall fading. A soil test showed low nitrogen levels in that bed. I added some balanced fertilizer and watched the new growth come in deep green within weeks.
The hydrangea yellowing leaves causes fall into clear groups when you know what to look for. Iron chlorosis shows that vein-green, blade-yellow pattern because iron can't move within the leaf once it arrives. Nitrogen shortage affects older leaves first since the plant pulls this nutrient from old growth to feed new growth. Too much water causes brown edges along with the yellow color.
Oregon State Extension breaks down hydrangea leaf problems by their warning signs. Brown crispy edges paired with yellow leaves point to too much water or poor drainage. Even, pale yellowing without brown edges suggests a nutrient gap. Yellow leaves only at the bottom of the plant often means nothing is wrong at all.
Old lower leaves turn yellow and drop as a normal part of growth. Your plant sends resources to new growth and lets go of shaded leaves near the base. This happens most in late summer as the plant shifts energy toward preparing for winter. Don't panic if just a few bottom leaves fade while the rest looks healthy.
Check your drainage first when you spot yellow leaves. Dig down a few inches after watering and see if soil stays soggy. Fix wet spots by adding compost to improve drainage. Test your soil pH if you see that chlorosis pattern. A reading above 7.0 suggests you need to add sulfur or iron sulfate to free up locked iron.
Treat nitrogen shortage with a balanced fertilizer in early spring. Look for something like 10-10-10 and follow the package rates. Avoid heavy feeding in late summer since this pushes tender growth that winter will damage. One good feeding in spring handles most hydrangea needs for the whole season.
Read the full article: How to Care for Hydrangea: Complete Growing Guide
