Incrediball (Hydrangea arborescens "Abetwo") is a smooth hydrangea cultivar notable for its enormous, long-lasting flower heads, which may be up to 12 inches in diameter. Incrediball is considered an improved version of the cultivar "Annabelle," boasting larger flowers and upright stems that prevent the flowers from flopping over. Like other hydrangeas, Incrediball requires specific cultural conditions and care in order to thrive.
Choose a Shady Site
Incrediball is hardy in U.S. Department of Agriculture plant hardiness zones 3 to 9, where it prefers a partially shaded location. A location with filtered sunlight or morning sunlight and afternoon shade is ideal. In consistently moist soils, the shrub will tolerate full sunlight, particularly in the northern end of its range. If planting multiple hydrangea shrubs, provide at least 5 feet of space between plants.
Maintain Moist, Fertile Soil
Incrediball requires well-draining, moderately moist soil. During drought, foliage tends to noticeably decline. Water deeply once a week to provide 1 inch of water. During hot dry spells, you may need to water twice a week to keep the foliage looking its best. Avoid splashing the leaves with water, as this invites fungal disease. Maintain a 2- to 3-inch layer of organic mulch over the root zone to help keep the soil moist and suppress weeds. Fertilize in early spring and again in summer, after flowering has finished, with 4 ounces of a balanced fertilizer such as a 10-10-10. Water after fertilizing and store unused fertilizer in a secure location away from children and pets. Do not fertilize in fall, when the shrub prepares for winter dormancy. Fertilizing does not affect the color of the flowers.
In early spring, prune weakened, dead or damaged stems. You can also revitalize the shrub by pruning it all the way down to the ground in late winter to encourage vigorous stem growth. This is a good strategy for shrubs that incur severe frost damage over the winter. Disinfect pruning equipment afterward by soaking tools in a solution that is 1/2 water and 1/2 rubbing alcohol for five minutes. Rinse with water and air-dry.
Treat Foliage Damage
Foliage may be damaged by pests such as aphids, mites and scale, as well as by common fungal diseases such as powdery mildew, rust, blight and leaf spot. Applying horticultural oil to the foliage will help combat these problems. Mix 2 tablespoons of oil per gallon of water, mixing thoroughly. Using a handheld or hose end sprayer, apply the entire plant, including the undersides of leaves, until all surfaces are wet. Apply every seven to 14 days until condition or pest infestation goes away. Store unused oil away from direct sunlight and food products.