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The Homeowners Column
Oakleaf Hydrangeas are a Hit
August 25, 2016
State Master Gardener Coordinator
These days you can't throw a rake without hitting a hydrangea. Their bodacious blooms of white, pink or blue orbs are everywhere.
Several species of hydrangeas are available, some with hundreds of cultivars. Each has its own quirks as to winter hardiness and shrub size ranging from three feet tall to twenty feet tall; as well as differences in flower color, flower size, and flower shape.
Few plants reward the organized gardener as much as hydrangeas. Save the plant label. The plant name can lead you to information about the care of your hydrangea and also what to expect in size and floral show. Their identification is crucial to their happiness in the landscape and to our happiness with them.
Hydrangea care can be confusing due to the differences in flowering among species and the myriad of new cultivars. The easiest ones to grow are panicle hydrangea, Hydrangea paniculata, and smooth hydrangeas, Hydrangea arborescens. They ﬂower on new wood (stems developed in the current growing season). Since the flower buds form after the plant starts to grow in spring, the severity of winter's cold doesn't affect them. In addition, pruning can be done in fall or in spring without fear of removing flower buds. Soil pH does not affect bloom color with these species.
Bigleaf hydrangea, Hydrangea macrophylla, mountain hydrangea, Hydrangea serrata, and oakleaf hydrangea, Hydrangea quercifolia, typically ﬂower on old wood (growth created in the previous season). Flower buds on these hydrangeas begin to form in late summer and must remain intact all through the fall, winter and spring in order to ﬂower the following summer. Severe winter's cold and/or pruning in winter or spring can translate into green leaves but no flowers. Bigleaf hydrangea is the most susceptible to flower bud injury; however, several new cultivars bloom on old and new wood. Mountain and oakleaf hydrangeas show good flower bud cold hardiness.
Oakleaf hydrangea, a southeastern U.S. native, is appropriately named for its leaves reminiscent of red oaks. The dark green leaves can reach eight inches long for a show stopper in the landscape. Their fall color is striking with leaves of red to purple that hang on late in the season. Flowers are typically white aging to pink held in 3 to 12-inch-long erect panicles on branch tips. Stems add interest of their own with their cinnamon colored exfoliating bark. Oakleaf's winter habit is not exactly beautiful but definitely interesting; as interesting as grandma wearing a mini skirt. You can't help but stare.
Oakleafs can be winter tender when young but once established they have few problems. Since they bloom on old wood, severe winter temperatures, below minus 10 degrees F, may kill terminal buds and no flowers will be produced the following season. Winter pruning also removes flower buds.
Hydrangeas including oakleafs prefer moist not soggy soils and some shade. Oakleafs have a unique characteristic among shrubs in their ability to flower in deep shade. They tolerate drier soils and sunnier areas compared to bigleaf hydrangeas.
Here are just a few oakleaf hydrangea cultivars:
'Alice' - 12 feet tall and wide. Flower panicles are a whopping 10 to 14 inches long.
'Munchkin'- introduction from U.S. National Arboretum breeding program; four feet tall and wide; flowers remain upright even after heavy rain.
'Pee Wee' – nice compact form at 3 feet tall and wide with proportionately smaller flowers. Some reported 'Pee Wee' as more "Pee Wow" with larger than listed growth.
'Ruby Slippers' – another U.S. National Arboretum introduction; 4 feet tall and 5 feet wide; flowers quickly age to pink.
Snow Queen™ ('Flemygea') - 6 feet tall; more compact in flower form and growth; good winter hardiness; red bronze fall color. Flower interest from June to November as their color ages like fine wine from white to pink.