Common Disease or Cultural Problems
Botrytis: This fungus causes a grey mold on flowers, leaves, stems and buds. It thrives in cool wet weather conditions. Burpee Recommends: Remove affected plant parts, avoid watering at night and getting water on the plant when watering. Make sure plants have good air circulation. Contact your Cooperative Extension Service for fungicide recommendations.
Cercospora Leaf Blight: Small flecks which develop a yellowish halo appear on the leaves and turn brown and coalesce. They cause the leaves to wither and die. Burpee Recommends: When watering avoid wetting the leaves. Contact your Cooperative Extension Service for fungicide recommendations.
Powdery Mildew: This fungus disease occurs on the top of the leaves in humid weather conditions. The leaves appear to have a whitish or greyish surface and may curl. Burpee Recommends: Avoid powdery mildew by providing good air circulation for the plants by good spacing and pruning. Contact your Cooperative Extension Service for fungicide recommendations.
Rust: A number of fungus diseases that cause rust colored spots on foliage and stalks. Burpee Recommends: For serious infections contact your Cooperative Extension Service for fungicide recommendations.
Virus (Various causes): The most characteristic sign of virus is tight and dark green mottling of the leaves. Young leaves may be bunched. Young plants may have a yellowish tone and become stunted. Burpee Recommends: This disease is readily spread by handling. Destroy diseased plants and the plants on either side.
Common Pest Problems
Aphids: Greenish, red, black or peach colored sucking insects can spread disease as they feed on the undersides of leaves. They leave a sticky residue on foliage that attracts ants. Burpee Recommends: Introduce or attract natural predators into your garden such as lady beetles and wasps which feed on aphids. You can also wash them off with a strong spray, or use an insecticidal soap.
Lygus Bugs (Tarnished Plant Bug): Lygus bugs are ¼ inch long and are green or brown with yellow markings. Nymphs are flightless and smaller than the adults. They suck on stem tips and flower buds and inject a toxic that deforms roots, stems and ruins flowers. Burpee Recommends: Because lygus bugs over winter in garden debris, remove all debris after the first frost. Contact your Cooperative Extension Service for insecticide recommendations.
Scale: Small bugs look like brown, black, gray to white bumps on the stems of plants. Scale may not have any apparent legs and may not move. Scales have a sucking mouth part. Scale may produce honeydew so leaves and stems may be sticky. Scale can weaken the plant causing it to grow very slowly and may wilt at the middle of the day. Burpee Recommends: Completely spray the stems with Insecticidal soap. For a severe infestation contact your local County Extension Service for recommendation for your area.
Spider Mites: These tiny spider-like pests are about the size of a grain of pepper. They may be red, black, brown or yellow. They suck on the plant juices removing chlorophyll and injecting toxins which cause white dots on the foliage. There is often webbing visible on the plant. They cause the foliage to turn yellow and become dry and stippled. They multiply quickly and thrive in dry conditions. Burpee Recommends: Spider mites may be controlled with a forceful spray every other day. Try hot pepper wax or insecticidal soap. Check with your Cooperative Extension Service for miticide recommendations.
Whitefly: These are small white flying insects that often rise up in a cloud when plants are disturbed or brushed against. Burpee Recommends: They are difficult to control without chemicals. Try hot pepper wax or insecticidal soap. Check with your Cooperative Extension Service for pesticide recommendations.
Does hydrangea make good cut flowers? Yes, but they do need some special care. Make a fresh cut. Plunge the end into very hot or boiling water for 30 seconds to seal the end before using it in an arrangement. Many hydrangea flowers are lovely dried as well.
How do I change the flower color of my hydrangea? You can only change the color of pink and blue-flowering macrophylla hydrangeas. Blue needs an acid soil (low pH) and pink needs an alkaline soil (high pH). Soil acidifiers lower pH and lime raises pH. Never change your soil pH by more than a half a point per year.
Why isn’t my hydrangea blooming? Several factors will affect hydrangea blooming. Young plants may only produce a few blooms in their first couple of years. If improperly pruned or pruned at the wrong time, flowering buds can be accidentally removed, and without flowering buds, there will be no flowers. If the winter was severe, varieties that bloom on old wood may have had their flower buds killed. Too much nitrogen in the soil, possibly from a fertilized lawn, will encourage green growth at the expense of flowers.
Why are my hydrangea flowers turning green? This is usually due to the high heat. As the flowers age they will develop some of their color back again. New flowers that are produced when it is cooler will have normal colors.
Can I grow hydrangeas in containers? Many smaller varieties are ideal for container growing. Use a commercial potting mix rather than garden soil, and regarding hardiness, consider yourself one hardiness zone colder when you choose a variety. Plants in containers are not as well protected in winter as plants in the ground.