When it rains, it pours mopheads and lacecaps

COLUMBIA, Mo. – Those billowy white panicles seen on flowering shrubs in late summer are not puffs of cotton candy, said University of Missouri Extension horticulturist David Trinklein. They are the flowering structures of Hydrangea paniculata, one of several hydrangea species that grow well in Missouri.

Fall is an ideal time to establish hydrangeas in the landscape.

Hydrangea is a genus of nearly 75 species of shrubs or small trees, most native to Asia and the Americas. The name comes from the Greek hydro, meaning “water,” and angeion, meaning “vessel.” Although the name comes from the shape of its seed pods, it is appropriate for another reason: “As a rule, hydrangeas require more water than most ornamental shrubs and should never be allowed to become drought-stressed,” Trinklein said.

Hydrangeas come in two main groups: mophead and lacecap. Mophead flowers are large, round and billowy. Lacecap flower heads are round and flat. They are composed of small, fertile florets surrounded by showier, sterile florets that create a lacy appearance. In both, what appear to be flower petals are showy sepals.

Panicle hydrangea (Hydrangea paniculata) is a woody, tree-like hydrangea that produces large clusters of white flowers that are somewhat pyramidal in shape. According to Trinklein, many consider it to be the easiest hydrangea to grow. It puts on a stunning display of large mophead flowers that dominate the landscape from late July to August.

Of the many named cultivars of Hydrangea paniculata, “PeeGee,” “Limelight” and “Dolly” are among the best, Trinklein said. If space is limited, the dwarf cultivar “BoBo” forms large panicles but achieves a mature height of only about 3 feet.

Hydrangea macrophylla, also known as bigleaf or florists’ hydrangea, has been an important greenhouse crop for decades. Individual flowers of bigleaf hydrangea have large, showy sepals surrounding a center core of smaller, less conspicuous flowers. This species has been dubbed the chameleon of hydrangeas, since the color of its flowers can be controlled by altering the plant’s soil environment. Flowers are pink if the plant is growing at a soil pH nearly or slightly above neutral. Aluminum sulfate can produce blue flowers by acidifying the soil, making the aluminum more readily available for plant uptake. The color of white hydrangea flowers cannot be changed.

Another popular hydrangea species is Hydrangea arborescens, often called smooth hydrangea. Unlike macrophylla, this species flowers on new growth. Although available only in white, it bears large, attractive flower clusters. Annabelle, a popular cultivar of smooth hydrangea, bears large white mophead flowers. Flower heads appear in late spring and can approach 12 inches.

Oak-leaf hydrangea (Hydrangea quercifolia) is attractive and well-adapted to Missouri’s climate. Its large, lobed leaves turn red in the fall. It grows and flowers well in shade and is a good choice for difficult, low-light areas, said Trinklein. Oak-leaf hydrangea produces white, somewhat pyramidal flower heads in early summer that gradually change to pinkish purple. It has relative few problems and deserves more attention than it receives, he said.

Generally, hydrangeas are relatively easy to maintain. Most species prefer a rich, well-drained garden loam. Optimum sun exposure varies by species, but in many cases, hydrangeas fail to bloom because they do not get enough sun. Soil should remain constantly moist but not wet.

Hydrangea species that flower on “new wood” (current year’s growth) should be pruned in late winter or early spring. Species that flower on “old wood” (growth from the previous year) often need very little pruning. When pruning is needed, it should be done shortly after flowering to allow for bud growth and development during the remaining growing season.

For more information, visit the website of the American Hydrangea Society.

Photos

• Hydrangea 1
• Hydrangea 2
• Hydrangea 3

Hydrangeas burst with blooms summer and fall in colors ranging from blues and white to lavender and pinks. Photos courtesy of Katie Kammler.