Hydrangea macrophylla is this most popular species of hydrangea grown in America, according to the National Arboretum. This Japanese native is a large, showy shrub desirable for its huge clusters of flowers. There are dozens of cultivars of this plant, according to the University of Connecticut. Some have "mophead" blooms, which are neatly rounded flower clusters, while others have "lacecap" blooms, which are a ring of showy flowers surrounding much smaller flowers.
This hydrangea needs relatively warm temperatures in order to flourish. It prefers temperate climates with mild winters and warm summers. These shrubs do not fare well in tropical or subtropical climates nor in very cold climates. Hydrangea macrophylla grows best in U.S. Department of Agriculture (USDA) plant hardiness zones 5B through 9A, according to the University of Florida.
H. macrophylla is not a full-sun plant. In fact, too much exposure to the harsh, direct rays of the afternoon sun, in particular, can scorch the thin, broad leaves of the plant or bleach out the colors of the flowers. Make sure your shrub is protected from the sun with some afternoon shade. In the hottest growing zones, this plant can be located in full shade.
Soil and Water
This hydrangea thrives in cool, moist soil. The soil should be nutrient-rich for best results. Mulching with organic materials can help retain moisture, add nutrients and stifle weed growth. Never let the soil around the plant remain hot and dry for very long, or the hydrangea will quickly begin to decline, according to the University of Connecticut.
Many home gardeners enjoy adjusting the pH level of the soil in order to change the color of the flowers of the H. macrophylla. Acidic soil (pH at 5.5 or lower) will produce blue flowers, according to the National Arboretum. Soil that is very alkaline in nature (6.5 or higher) will cause the plant to bloom with pink flowers. Amend the soil around the bush in the spring with lime to raise the pH levels, or with aluminum sulfate to lower the pH levels.
Prune your H. macrophylla immediately after the flowers being to fade. This plant blooms on last year's growth. If you prune before flowering, you will remove the growing buds, according to the University of Florida, and the hydrangea will not bloom at all in the current season.