7 Reasons Your Hydrangea Leaves are Turning Yellow

Yellow leaves on hydrangeas spoil the symmetrical appearance of these large-leaved shrubs. Hydrangea foliage, which ranges in color from medium to dark green, provides a contrasting backdrop for the blooming flowers.

Different types and degrees of leaf chlorosis help identify and correct the problem. If your foliage has lost its shine, consider seven possible causes of yellowing hydrangea leaves and tips for restoring the plant to its best form.

Improper Watering

A good place to start is by looking at moisture issues. These problems are easy to identify and correct if you take action before the roots rot. A moisture meter can help you find the best solution.

Overwatering

Large leaves often appear drooping in the afternoon heat. If they don’t grow well in the evening or still look wilted in the morning, your plants may have been overwatered. The tender leaves turn yellow, then turn brown and soft, and then gradually fall off. Other signs include slower growth, fewer flowers, and wilting flowers. Plants may develop root rot.

Test the soil moisture around the base of the tree by poking the soil about 4 inches with your finger or using a moisture meter. If the soil is too wet and soggy, overwater the hydrangea. Keeping water until the soil dries out can solve this problem, but if the foliage continues to yellow and wilt, more drastic measures need to be taken.

Remove the plant from the soil and trim off any roots that are not white or plump (full).
Replant the plant in a new location or add some sand to the soil for better drainage.

Underwatering

Lack of watering also causes leaves to turn yellow with brown and brittle edges. Don’t try to solve the problem by overwatering. This may make the situation worse.

Water deeply until the surface of the soil is slightly moist. You may need to increase the frequency. Remember that deep watering two to three times a week is usually sufficient. Add mulch to retain soil moisture.

Poor drainage
Hydrangeas grow better in loamy, sandy soil than in clay soil. This increases the likelihood of flooding.

Choose a site with well-drained soil and avoid areas with puddles of rainwater. Test the soil’s drainage capacity by digging a hole 6 to 8 inches deep, filling it with water and observing how quickly it soaks up. Adding compost and sand to the soil around existing hydrangea plants will help improve drainage.

Improper sun exposure
Some hydrangea varieties are more tolerant of direct sunlight, but most prefer morning and afternoon sun. Avoid improper sun exposure by choosing a suitable location or, if possible, relocating the bush.
Burnt leaves
Too much direct sunlight during the hottest part of the day can cause leaves to turn yellow, brown and brittle.

Insufficient lighting
When plants don’t get enough sunlight, photosynthesis slows and disrupts the production of chlorophyll, the nutrient that keeps leaves green.

Poor land
Growing in poor quality soil contributes to many of the problems that cause yellow leaves, including improper watering, nutrient deficiencies, and disease. You can do a test at home to check the correct pH level. With that said, a sample tested by your local Cooperative Extension office will give you more information about nutrient deficiencies and soil quality.

Soil pH is incorrect
Hydrangeas require slightly acidic soil with a pH between 5.0 and 6.5. Increase soil pH by adding lime. Add aluminum sulfate to lower the pH.

Nutrient deficiencies
Nitrogen
Nitrogen deficiency often occurs in the spring, causing leaves to turn yellow and fall prematurely. Plants use a lot of nitrogen and can quickly deplete the soil. Composting and applying a balanced spring fertilizer for acid-loving plants will help solve this problem.

Iron
When new leaves turn yellow but the veins are still green, the hydrangea is likely lacking iron. This occurs due to overwatering, poor drainage, improper fertilization and highly alkaline soil.

Treatment with chelated iron will quickly correct chlorosis, but soil fertilization is necessary to correct the underlying problem. Check the pH and take necessary measures to increase the acidity. Look for a fertilizer for acid-loving plants that contains iron. Compost with oak leaves, pine needles and coffee grounds helps increase soil acidity.

Magnesium
Magnesium deficiency is less common and appears as yellow leaves and green veins, but only on older leaves. Hydrangeas grown in soil are often magnesium deficient. This makes the problem a little more difficult to solve.

Epsom salts and dolomite lime add magnesium, but lime also raises the pH and should be used with caution. Try spraying the leaves with liquid seaweed extract. Avoid fertilizers high in potassium as they interfere with magnesium absorption.

Improper application of fertilizers
Applying too much or not enough fertilizer or using the wrong product will affect all parts of the plant and cause leaves to turn yellow. Use products designed for acid-loving plants, such as hydrangeas and azaleas, and follow package directions.

Sick
Hydrangeas are susceptible to fungal, bacterial and viral infections. Hydrangea mosaic virus and tomato ringspot virus cause yellowing of leaves.

Good hygiene helps prevent mosaic virus. Use sterile pruning tools and spray pruning shears between cuts to prevent possible spread. Tomato ringspot virus is caused by nematodes. Look for varieties that are disease resistant.

pests
Pests carry and spread diseases, and the two-spotted spider mite causes leaf discoloration and damage to hydrangeas. Then white and yellow spots appear, forming holes and finally loss of leaves. Early signs of spider mites include thin webs. Check the undersides of the leaves for damage and apply neem oil or horticultural oil.