Primarily known as a source of summer color flowering June through August — long after most shrubs have finished. Hydrangeas’ interesting bark and flower heads can also provide winter texture when left untrimmed until spring. Four species are commonly used in Kentucky landscape plantings.Big Leaf Hydrangea is the most widely used hydrangea species. Its large flowers range from white to pink to blue. While white cultivars remain white, pink or blue cultivar color is determined by soil pH and availability of aluminum. A soil pH range between 5.0 to 5.5 will generally produce the blue flowers, and a pH of 6 and above inspires pink flowers. Most cultivars of this species bloom on the previous season’s wood. If temperatures drop too low, the flowers for the next season will be lost. New selections like “Endless Summer” bloom on current season’s growth, providing blooms even if flower buds are killed by late spring frosts.
Smooth Hydrangea is popular for its large, white blooms from June to September every year on new growth. Removing the flowers as they turn brown will encourage a second flush of flowers in August. Part shade is best in locations where the weather is generally hot and dry. This hydrangea grows three to five feet tall, making it a possible choice in smaller landscape spaces. There are several good cultivar selections, but the most popular is “Annabelle.”
Panicle Hydrangea is one of the larger shrubs growing six to ten feet tall and six to ten feet wide depending on the cultivar. This plant will grow best in full sun. Enjoy the white to purplish-pink flowers from June to September. Blooms can be pruned when they turn brown or during the winter. One popular selection of this species is “Limelight” with large, light green flowers that mature to white.
Oak Leaf Hydrangea, native to the southeastern United States, is known for its large, oak leaf-shaped foliage, and is a popular landscape choice for areas with part shade. The white to purplish-pink flowers are four to twelve inches long with three- to four-inch wide panicles. The flowers are abundant and fragrant. In the fall, the foliage turns to shades of red, orange-brown, and purple, adding additional color to the landscape.
Submitted by Michael Boice, Extension Program Assistant Horticulture and Lauren State, Extension Staff, Oldham County