Look closely at gardens around Lawrence right now and you will see shrubs here and there with giant softball-sized (or even a little larger) flower heads dispersed throughout the plant like giant ornaments on a Christmas tree. The shrubs are hydrangeas, and are available with flowers in a range of colors, including white, green, pink and even bright blue.
Hydrangeas have a long bloom time, with flower heads that can also be dried for fall arrangements. Before blooms appear in spring, the shrub is a rounded, deep green mass that fades into its surroundings in the landscape. Hydrangeas are a good option for a medium-sized shrub to fill along a foundation or border and provide midsummer to fall color.
The major downside of hydrangeas is their thirst — they will need supplemental water in a hot Kansas summer even after being established. Some varieties also require more maintenance than others to maintain kempt plants and achieve certain flower colors.
The hardiest and least needy of the thousands of hydrangeas on the market are known as smooth hydrangeas, or Hydrangea arborescens. The species is a native woodland plant of the eastern and central U.S. Smooth hydrangeas grow best in partial shade with ample water.
One of the most popular cultivars of this species is Annabelle, which was discovered in the wild decades ago and cultivated for its exceptionally large showy blooms.
In more recent years, plant breeders have released the new smooth hydrangea cultivars Incrediball, White Dome, Grandiflora and Invincibelle Spirit, among others. They are considered improved varieties in their own right — for example, Incrediball and Grandiflora produce showier blooms than Annabelle, with stronger stems that remain more upright. Invincibelle Spirit has pink flowers, and White Dome produces dome-shaped flower heads rather than rounded ones like the other cultivars.
Another excellent choice for part sun/part shade locations are oakleaf hydrangeas, Hydrangea quercifolia. Oakleaf hydrangeas are native woodland plants of the southeastern United States. At one time they were considered to be marginally cold-hardy in the Lawrence area, but this is more of a rumor than a fact. True to its name, the leaves of oakleaf hydrangea are shaped like oak tree leaves.
Oakleaf hydrangea flower heads are more cone-shaped than other hydrangea flowers. Because of the large, rough leaves and coarse stems, the plant overall has a coarse texture and is best for a foundation planting or for the back of a large landscape bed with softer plants in front.
Oakleaf hydrangeas also have a pleasing fall color and reddish, peeling bark that adds interest to the garden in fall and winter.
The most popular and varied group of hydrangeas are bigleaf hydrangeas, Hydrangea macrophylla. This group includes the Endless Summer series, Blushing Bride, Nikko Blue, Bloomstruck, and a few hundred others. Some varieties have cold-hardiness issues in the Lawrence area, so select with care. Most bigleaf hydrangeas also need well-drained fertile soil with high organic matter content and ample water to survive.
Bigleaf hydrangeas are popular because they offer a wider range of colors (including the ever-popular blues). This group includes the varieties that can turn bright blue in acidic soil or appear pink to white to green. Bigleaf hydrangeas tolerate more shade than other varieties, but they wilt easily with too much sun.
Panicle hydrangea, Hydrangea paniculata, produces a large, cone-shaped flower head. It is very winter-hardy but requires fertile soil and ample moisture like bigleaf hydrangeas. Pee Gee is one of the most popular varieties along with Bobo, Pinky Winky and the more recent introduction Limelight.
— Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation.