White hydrangeas are a deciduous shrub blooming from late spring through the summer with large white flowers against dark green foliage. A hardy, virtually pest-free shrub, hydrangeas are considered an old-fashioned plant that have been grown in gardens for years. There are three popular cultivators of the white hydrangea--H. arborescens "annabelle," H. quercifolia "snowflake" and H. paniculata "tordiva"--and depending on the variety, these shrubs grow from 6 to 10 feet tall. Growing white hydrangeas is relatively easy.
Plant the white hydrangea in a location that receives at least six hours of full sun daily with partial shade in the late afternoon. Although hydrangeas can withstand hot conditions, hot afternoon sun can cause the shrub to wilt.
Grow white hydrangeas in soil that is well-draining but moist. Amend the soil with compost before planting the shrub. Plant in the spring after the last frost.
Water on a regular basis, once a week, to supply the shrub with at least 1 inch of water per week. Deep watering is necessary and can be achieved using a soaker hose or drip irrigation system.
Apply a balanced, slow-release fertilizer twice a year in the early spring and again in early fall. Use a granular higher phosphate formula, 10-30-10, and apply according to the manufacturer's directions. Phosphate is the second number on fertilizer bag, while nitrogen is the first. Too much nitrogen produces more foliage and less blooms.
Add a 2- to 3-inch layer of mulch around the base of the plant out to the drip line or the outermost branches. Use an organic mulch such as shredded bark, chopped leaves or compost, which will help to enrich the soil as it works its way in. Reapply mulch every spring as needed.
Prune white hydrangeas in late summer when done blooming. Remove dead stems and old flowers, then cut back healthy stems to approximately 12-inches in length. Dead-heading, or cutting off spent flowers, throughout the blooming season will encourage an increase in blooms.