Hydrangea (Hydrangea macrophylla) is a favorite garden plant that provides color after most spring flowering shrubs have finished blooming. Hydrangeas grow best where they get morning sun and afternoon shade. An interesting feature of the hydrangea is that the Ph level of the soil influences the color of the blooms. Alkaline soil produces pink blooms and acidic soil encourages blue blooms.
Types of Problems
Common problems when growing hydrangeas are insect problems such as aphids and spider mites, lack of blooms, sun scorch, powdery mildew, fungal problems, and rust.
Aphids are easily seen as they crowd around stems and flower buds. They are small insects that secrete a sticky substance that encourages mold growth.
Spider mites are identified by yellowing of the leaves from the ground up. They are tiny brown insects that live on the underside of leaves. Take a yellowed leaf and hold over a sheet of white paper. Thump the top side of the leaf and the spider mites will fall to the paper and can be easily seen.
Sun scorch can be seen on plants exposed to too much sun. Yellowing of leaves along with irregular brown spots on the leaves are signs of sun scorch. Also, the plant will wilt completely during the hottest part of the day, but recover in the evening.
Powdery mildew looks like the plant was dusted with talcum powder and spreads rapidly.
Fungal problems show up as brown or gray spots on leaves and flowers. The plant will wilt but does not recover when provided water. Watering the plant often makes the problem worse.
Aphids affect the vigor and health of the plant and can spread other diseases to the plant.
Spider mites lead to a decline in the overall health of the plant and cause distorted growth.
Sun scorch will stunt the plant's growth and affect the number of blooms.
Powdery mildew rarely kills the hydrangea, but affects how the plant looks in the landscape.
Fungal problems will lead to an overall decline in the health of the plant and may be fatal.
Rust appears as orange spots that appear on the underside of leaves and makes the plant unsightly.
Aphids are controlled by applying neem oil over the insects then removing with a strong blast of water after 24 hours.
Spider mites can be killed by spraying with neem oil or dusting with pyrethrum dust. Also, a strong spray of water to the underside of the leaves will dislodge them and lower the population.
Lack of blooms usually occurs when a frost kills new flower buds or incorrect pruning methods. Hydrangeas bloom on the previous year's growth. If warm weather encourages new growth and buds and then they are exposed to freezing weather, the flower buds can be killed. Pruning new wood will eliminate flowering branches that would produce blooms the following year.
Prevent sun scorch by planting the hydrangea in a location that gets morning sun and shade in the afternoon.
Control powdery mildew by spraying leaves with neem oil at the first sign of the disease and repeating every 3 days until the mildew is no longer present.
Prevent fungal problems by providing good drainage to the planting area and avoid splashing water on the leaves during irrigation.
Buy hydrangea plants from a nursery. Hydrangea plants purchased in a florist shop don't always do well in the garden. Planting location is the most important factor for success when growing hydrangeas. Afternoon shade and a well drained location goes a long way toward preventing problems. Fertilize with a fertilizer specially formulated for hydrangeas. There is a variety of hydrangea called the "endless summer hydrangea" that blooms several times over the growing season.