Native to the United States, Annabelle hydrangea was first discovered growing in the wild near Anna, Illinois. Popular in the northern part of the country for its cold tolerance, Annabelle hydrangea blooms on new wood and produces huge flowers reaching up to 14 inches in diameter. Hardy to USDA zone 4, the plant's new wood typically freezes back during winter in cold climates, but blooms reliably each year from flower buds formed in spring. Resistant to disease and requiring only minimal care, Annabelle hydrangea thrives in a shady border or when combined with other large shrubs.
Plant Annabelle hydrangea during mid-spring after all danger of frost has passed in a location that receives partial shade throughout the day and consists of rich, well-drained, moist soil. Space Annabelle hydrangea plants 3 to 6 feet apart.
Spread a 2- to 4-inch layer of mulch over the ground surrounding Annabelle hydrangea to insulate the soil and improve its moisture retention. Start the layer at least 4 inches from the plant's base to allow air circulation, which reduces the risk of disease.
Water Annabelle hydrangea once every five days during the spring and summer months to keep the soil moist at all times. Decrease the frequency of watering to once every week during fall and once every two weeks during winter, when the plant is not growing actively. Apply at least 6 inches of water at each watering.
Feed once per year during early spring for the first two years of growth to help establish the planting. Use a slow-release fertilizer to gradually release nutrients throughout the growing season. Apply following the manufacturer's instructions for proper dosage.
Prune Annabelle hydrangea plants once per year during late fall, winter or early spring, just before new, active growth resumes. Use hedge clippers to cut the plant back to 10 to 12 inches in height, which will produce stronger stems and bigger flowers.