Hydrangea leaves may turn yellow due to a lack of essential nutrients, particularly nitrogen, iron, or magnesium. Nitrogen deficiency often causes older leaves to yellow first, as the plant redirects nitrogen to newer growth. Iron deficiency, known as chlorosis, leads to yellowing between the veins of young leaves, while magnesium deficiency results in yellow patches between leaf veins, starting with older leaves. To address this, use a balanced fertilizer or specific supplements like iron chelates or Epsom salts (for magnesium).
Hydrangeas thrive in slightly acidic to neutral soil (pH 5.5–6.5). If the soil is too alkaline, the plant may struggle to absorb iron, causing yellow leaves. Conversely, overly acidic soil can lock up other nutrients. Test the soil pH and amend it accordingly. For alkaline soils, add sulfur or peat moss to lower the pH. For excessively acidic soils, apply lime to raise the pH gradually.
Yellowing leaves can signal root rot caused by overwatering or poorly draining soil. Hydrangeas prefer moist but well-drained soil. Soggy conditions suffocate roots, preventing nutrient uptake. Ensure the planting site has good drainage, and reduce watering frequency if the soil feels waterlogged. Mulching can help retain moisture without causing excess wetness.
Insufficient water can also cause yellow leaves, as the plant struggles to transport nutrients. Hydrangeas need consistent moisture, especially during hot, dry periods. Wilting and crispy leaf edges often accompany yellowing in drought-stressed plants. Water deeply and regularly, ensuring the root zone stays evenly moist but not saturated.
Pests like spider mites, aphids, or scale insects can weaken hydrangeas, leading to yellow leaves. These pests suck sap from the foliage, disrupting nutrient flow. Check the undersides of leaves for tiny insects or webbing. Treat infestations with insecticidal soap, neem oil, or horticultural oils, ensuring thorough coverage.
Fungal or bacterial diseases, such as leaf spot or powdery mildew, can cause yellowing leaves. Leaf spot appears as discolored patches, while powdery mildew coats leaves in a white film. Remove affected foliage and improve air circulation by pruning overcrowded branches. Apply fungicides if necessary, following label instructions.
Extreme temperatures, excessive sunlight, or harsh winds can stress hydrangeas, resulting in yellow leaves. Panicle and smooth hydrangeas tolerate more sun, but bigleaf varieties prefer partial shade. Protect plants from scorching midday sun or frost by relocating potted hydrangeas or providing shade cloth.
Older leaves naturally yellow and drop as part of the plant’s growth cycle. If only a few lower leaves are affected and the rest of the plant appears healthy, this is likely normal senescence. Simply prune the yellowed leaves to maintain aesthetics and redirect energy to new growth.
