Numerous species of fungus may attack hydrangea leaves, causing unattractive brown spots. Prevent fungal disease by keeping water off the leaves whenever you irrigate. Although some afternoon sunlight promotes blooms, too much sunlight, when coupled with wet leaves, can cause fungal spots. Hydrangeas generally prefer dappled shade. Prune off and destroy damaged or diseased leaves, and clear up any dropped flowers and plant debris from under the shrub. Disinfect pruners with household disinfectant before use and between pruning each shrub to avoid spreading disease. Provide at least 6 feet of space between shrubs to allow for ample air circulation. It is highly important to remove any diseased leaves that have fallen from the plant as well as hand picking highly infected leaves from of the plant. Be sure to discard these disease leaves in the trash, and do not put into the compost bin.

Support your hydrangea by providing it with the proper cultural conditions. Only plant hydrangeas where hardy: Bigleaf hydrangea (hydrangea macrophylla), the most widely cultivated species and the one your photo shows, is hardy in U. S. Department of Agriculture plant hardiness zones 6 to 10. Most hydrangeas prefer well-draining, rich soil. Check occasionally for pests such as aphids and scale insects, which can cause leaves to shrivel and turn brown. Wash off pests with a direct stream of water. Avoid the use of broad-spectrum insecticides, which kill beneficial predatory insects and can scorch leaves if overused.