Hydrangeas are beautiful flowering bushes that have been around for a long time. They come in a great many varieties from very large, to very small, and make themselves at home in all types of settings. Typically easy to care for, the hydrangea does have some problems that are perplexing to their growers. Getting a jump on those problems is the best way to ensure lovely flowers for your garden and cuttings for your house.
Powdery mildew attacks the "bigleaf" varieties of hydrangea most. Mildew loves the same conditions hydrangeas adore: shade and humidity. Carefully inspect the leaves of your plants regularly for any sign of mildew. Powdery mildew appears as a whitish powder or as purple spotting. Prune off damaged leaves to prevent spread, and burn, or bury them far away from the planted area.
A purple halo around brownish spots on the leaves of all types of hydrangeas is a sign of a fungus usually found in plants kept in full-sun. Like mildew, fungus will not kill your plant, but it is not pretty. Prune any leaves found with the disease and burn, or bury deep far from the garden area.
Root rot, and more specifically Armillaria root rot, is much more disastrous to hydrangeas than mildew or fungus. Too much water or soil that does not drain well keeping water at the base of the plant causes root rot. Your hydrangea will look wilted but will not perk up when you water it. Root rot will kill the plant. Prevention is the only cure for this problem. Make sure all soil drains well and you do not overwater your plants.
Aphids, Japanese beetles and mites are the big garden pests that destroy plants in various stages of growth. They get out of hand quick and kill swiftly if not kept in check. Japanese beetles are easy to spot. Spray plants with "Sevin," a commercial herbicide preparation found in most garden supply areas as soon as you see any sign of the bug. Early in the growth cycle and in the spring, Aphids cause problems on tender new leaves. Turn over leafs regularly and inspect for small, greenish bugs. Wash off with soapy water to protect the plant. Mites are the biggest problem when weather is the hottest. Dry leaf material is delicious to them. Keep your plants well nourished to avoid mite infestations. Rose chafers attack the flowering part of the plant when it blooms. Look for grayish colored beetles on the blooms of your plant and pick them off to solve the problem.
Iron deficiencies turn the beautiful green leaves of hydrangeas yellowish. Put garden fertilizers containing chelated iron on the soil when preparing a garden bed for hydrangeas and incorporate it into the soil yearly as long as the pH level is high.