University of Vermont Extension 
Department of Plant and Soil Science

Summer News Article


HYDRANGEAS

Dr. Leonard Perry, Extension Professor
University of Vermont
 
Easy to grow, hydrangeas include old-fashioned selections as well as many more recent ones.  Many have attractive bark and shapes, they come in a range of colors, flowers add color to mid and late summer landscapes, and they make good cut or dried flowers. 
           
To choose the most appealing hydrangea, you should be aware of the several flower types.  What we call "flowers" are actually clusters of flowers, both fertile and sterile.  The showy large parts are the sterile flowers that attract the pollinators to the less showy fertile flowers.  The amount of each varies with cultivar (cultivated variety). 
           
Then there are clusters that are long and conical (known as panicles), or flat to convex (known as corymbs).  If this latter type is flat, they're called "lacecaps".  If they resemble large balls, they are called "hortensias" or a name I like "mopheads". 
           
Hydrangeas prefer a moist but well-drained, and fertile, soil.  Plant in full sun to part shade.  They can be used in masses, against an evergreen background, as a specimen plant, or for fresh and dried arrangements.  Flowers of the panicle hydrangea turn a pink fall color, then a nice tan that remains through winter, as do flowers of the smooth hydrangea.
           
Not counting the climbing hydrangea (anomala subsp. petiolaris), a decidious woody vine hardy to USDA zone 5 (-10 to -20 degrees F average winter minimum), there are four main shrub species.  The smooth hydrangea (arborescens) grows about 3 to 5 feet high and wide, with rounded white flower clusters of mainly sterile flowers that begin green, and are long lasting.  Since they bloom on current season's growth, their flower buds aren't winter killed.   Plants are hardy to USDA zone 4 (-20 to -30 degrees F average winter minimum).  For best floral effect and overall plant shape, cut old stems to the ground in late winter or early spring.  This species adds color to woodland gardens, as well as old-fashioned gardens.  The species is native to mountains of the eastern U.S.
          
'Annabelle' is a common and excellent cultivar of the smooth hydrangea, with large flower clusters 10 to 14 inches wide.  'Grandiflora' is a cultivar often called snowhill or hills-of-snow, similar to 'Annabelle' only with smaller flower clusters.  White Dome is a patented new cultivar similar to 'Annabelle' only more vigorous and upright, the flowers tending not to droop with rain.
           
The big-leaf or French hydrangea (macrophylla) is the classic one most know, has most of the newest cultivars, and tends to be the least hardy (USDA zones 5 and 6).  Depending on cultivar, flowers may be either mophead or lacecap types.  These are the ones known for changing color with the soil acidity.  Acid soils free up aluminum, which is what causes deep blue to purple colors.  Alkaline soils result in shades of pink.  This shrub, native originally to Korea and Japan, tolerates salt such as along roads and the seacoast.  Most cultivars reach about 4 feet high and wide.  They seldom need pruning, but if so, prune right after bloom as these flower on the previous season's growth.
          
'Nikko Blue' is one of the older and more common big-leaf cultivars, getting some of the deepest blue colors on its mopheads in acid soils, and is hardier than most.  Similar is 'All Summer Beauty'.   'Red Star' gets red to purple-red on its lacecap clusters in alkaline soils, and has attractive fall color.  'Variegata' is interesting both for its white, irregular margins on leaves, and its pink or blue fertile flowers in lacecaps surrounded by white infertile flowers. 
           
There are several more compact big-leaf cultivars having mopheads in shades of pink. These include 'Pia', Forever Pink', 'Tovelit', and 'Glowing Embers'.  Arguably the most publicized new cultivar in recent years is Endless Summer, touted as having pink or blue mopheads on old and new wood most the summer.  Although listed as hardy to USDA zone 4, in my garden in this zone it dies back in winter, with new growth each summer, but never blooms.
           
Then there are the panicle hydrangea (paniculata) cultivars, familiar to many with their large elongated clusters of sterile white flowers, often seen around Victorian homes. Depending on cultivar, these can reach 6 to 10 feet tall and wide, or more.  Native to eastern China and Japan originally, these bloom on new wood so should be pruned in late winter or early spring to keep them more tidy.  They tolerate a wide range of soils if well-drained, tolerate urban pollution, and are hardy to at least USDA zone 4.
           
The most common panicle cultivar is 'Grandiflora', usually known by the initials of the species and cultivar names "P.G." or Pee Gee.  This old-fashioned plant is hardy to USDA zone 3 (-30 degrees F or below average winter minimum), and can reach 20 feet tall and wide making a vase-shaped specimen if pruned.  Or, it can be pruned into a single stem with flowers on top, known as a "standard" or "tree form".  'Pee Wee' and 'Compacta' are smaller versions, only reaching about 4 or 6 feet high and wide, respectively.  Other nice selections of the panicle hydrangea include 'Limelight' with lime green blooms, 'Pink Diamond' with white flowers turning pink early, 'Tardiva' blooming late, 'Unique' with larger individual flowers than Pee Gee, and 'White Moth' with flowerheads up to 14 inches.
           
The Oak-leaf hydrangea (quercifolia) is one I grew up with in the south, it being native to woodlands and stream banks of the southeastern U.S.  Where it survives into USDA zone 5 it is handsome for its irregular spreading growth, peeling brown bark, large oak-shaped deep green leaves, and reddish fall color.  It grows in shade, or full sun in the north.  Since this blooms on old wood (the previous year's growth), prune right after flowering before next year's buds begin to form. It tends to grow slower than some of the other hydrangeas.
           
Although the species is a good plant, there are several cultivars you might consider of the oak-leaf hydrangea.  Snow Queen has larger flower panicles than the species, is showier, and has more upright stems on plants about 5 feet high and wide.  'Snowflake' may get slightly larger, and has large, showy, double flower panicles.  Perhaps the largest cultivar, up to 15 feet tall and wide, with both large florets and clusters, is 'Alice'.  'Pee Wee' and 'Sike's Dwarf' are compact forms, only reaching about 3 feet high and wide.
           
If you want to dry hydrangea blooms, especially the panicle ones such as Pee Gee, there are a couple methods.  Although tempting to pick blooms at peak, they often dry best when cut if they've dried some on the plant already.  The pink tints, if present, hold when dried and give a vintage effect. 
           
Cut long stems, removing leaves, and put in a vase with or without water. Keep in a dry room, away from direct sun.  Or, you can use the traditional drying method of cutting stems and removing leaves, then hanging upside down in bunches in a warm, dry, and dark space with good air circulation.  Flowers should be dry in a couple weeks.
            

Return to Perry's Perennial Pages, Articles uvmext logo