If versatility is a virtue, then the wonderfully
diverse family of flowering hydrangeas is as good as they come. One is a shrubby vine that uses aerial
rootlets to cling tenaciously to walls or scramble sideways along an obliging
fence. A few excel at lighting up
shade-dappled woodlands. Others are
blowsy stars of sunny, late summer gardens, their flowers of blue, mauve, pink
and white lending a lush, romantic feeling to the dog days of late July, August
and September.
Mophead
Hydrangea, Bigleaf Hydrangea, Florist’s Hydrangea (Hydrangea macrophylla)
Hydrangea comes from the Latin for “water jar”,
referring to the shrub’s cup-shaped seed vessels. But old-fashioned bigleaf hydrangea deserves the nickname since
it demands copious amounts of water, both in the garden and as a popular
Easter-season flowering houseplant.
Although this hydrangea is now
usually classified as a true species, when it was discovered in the 1770’s in
Japan by Carl Thunberg, it was known to be a garden form resulting from complex
hybridizing of H. maritima, a seaside
species, and one or more Japanese woodland hydrangeas. Thunberg himself named it Hydrangea x macrophylla, the “x” denoting its hybrid nature. But this is interesting because it explains
why bigleaf hydrangea, both in its “hortensia” (spherical heads of sterile
flowers) and “lacecap” form (flat corymbs of fertile flowers surrounded by a
ring of sterile flowers), is very salt-tolerant and thrives in cool seaside
gardens, especially in the mild Pacific Northwest and along the lower Atlantic
seaboard.
Bigleaf hydrangea grows from 3 to 6 feet (1-2
meters) tall, depending on the cultivar and the climate (it grows taller in
milder areas.) It enjoys sun or light
shade and humus-rich, moist soil, preferably with a summer mulch to keep the
roots cool. In acidic soil, the blue cultivars will be more vividly
blue; soil on the alkaline side favors the pink cultivars. Tinkering with the pH by adding aluminum
sulphate or iron sulphate to acidify the soil eventually turns blue-flowered
cultivars pinkish-mauve; adding lime or a high-phosphorus fertilizer to raise
soil alkalinity turns pink cultivars blue.
Rejuvenate bigleaf hydrangea when necessary by removing 3-5 of the
oldest stems at ground level in late winter, while the shrub is still dormant.
Hardiness is the biggest negative. In colder areas (U.S Zone 5, Can. Zone 6)
the roots often over-winter while the top-growth died back to the
ground—self-defeating since most H.
macrophylla cultivars bloom on buds made the previous year. The exception is ‘Endless Summer’, a
vigorous hydrangea that flowers on new growth and has pink or blue flowers,
depending on soil pH. Other hortensias
for warmer climates are ‘Nikko Blue’, the old favorite ‘Seafoam’ and compact ‘Altona’
with large blossoms that range from dark pink to blue-purple. The hardiest lacecap is said to be ‘Blue
Billows’.
As the flowerheads of this hydrangea dry, they go
through a number of color changes, blue, mauve, lavender, purple and eventually
turning mottled green. These sensuous
colors make them popular with dried flower arrangers—and pricey too! To dry your own hydrangeas, start them off
in water, then hang them upside down in a dry, warm, dark place.
Climbing Hydrangea
(Hydrangea petiolaris)
Native to Japan, Korea and Taiwan, this shrubby vine
can climb more than 25 feet (8 meters) up a strong wall. Slow to establish, it 
seems to crawl by inches for the
first few years, finally clambering with gusto as it sends out woody stems
covered with lustrous, dark green leaves.
In late June and early July, climbing hydrangea is literally smothered
with large, flat, slightly fragrant, creamy-white blossoms composed of small,
fertile, inner flowers ringed by large sterile, outer sepals. With its peeling bark and long-lasting
flower bracts, it is attractive, even in winter.
Climbing hydrangea is often recommended as a good
vine for shade but it actually blooms poorly in a north-facing site, making its
best flowering show in moist soil in full sun.
In his book Gardening with Trees
and Shrubs, Ottawa plantsman Trevor Cole recommends planting it on an
east-facing wall at the limit of its cold-hardiness (Can. Zone 5b) since south
walls heat up too much in winter, which can prove fatal to the shrub. In milder winter areas, it can be planted
facing south or west.
Pruning is not required unless you want to keep the
vine compact. In that case, prune it
back immediately after flowering.
Japanese hydrangea vine (Schizophragma hydrangeoides) is very similar in appearance and
sometimes confused with climbing hydrangea.
Although related, it has only one sepal on the outer flowers, giving it
a more fragile appearance that climbing hydrangea, which has four sepals.
Oakleaf Hydrangea (Hydrangea quercifolia)
Native to Florida, Georgia and
Mississippi, this hydrangea is not likely to reach its optimal size except,
perhaps, in mild gardens on the West Coast.
Still, it is a beautiful shrub with much to recommend it.
Oakleaf hydrangea needs moist, humus-rich, acidic
soil in full sun or part shade. Its
leaves are leathery, dark green, and shaped like those of white oak (hence the
name). In October, they turn rich
burgundy-red. White flower panicles
bearing both showy sepals and small fertile blossoms appear in June and July,
the sepals often turning pink as they age.
Hardy to Zone 5b, oakleaf hydrangea grows to 6 feet (2 meters) high and
slightly wider. Like bigleaf hydrangea,
it flowers on old wood, so pruning should be done immediately after
flowering. Although there are many
named cultivars that grow much taller, to 12 feet (4 meters) with spectacular
long flower panicles, they tend to be more tender than the species.
A woodland edge plant, oakleaf hydrangea is lovely
in a shrub border with other acid-loving shrubs like blue holly (Ilex x meservae), Oregon grape holly (Mahonia
aquifolium), redvein enkianthus (Enkianthus
campanulatus), downy serviceberry (Amelanchier
canadensis), azaleas and rhodondendrons (Rhododendron spp.)
Peegee or Panicle Hydrangea (Hydrangea paniculata ‘Grandiflora’)
Native to Japan, Russia and China, peegee hydrangea
is a reliable, old-fashioned shrub or small tree for the late summer
garden. It derives its common name from
the joined initials of its species and cultivar names.
Hardy to Zone 3b, peegee hydrangea
needs sufficient sun and moist soil to put on a good flowering show, but light
shade in the hottest part of the
afternoon is appreciated. The
showy, cone-shaped, white flowers form on growth made in the current season, so
pruning needs to be done in early spring.
This is one shrub that needs the gardener’s intervention, not just for
flowering but for vegetative growth too, since unpruned plants languish and
sprawl and eventually stop flowering altogether. Prune back to just above the second or third strong bud on last
year’s wood to promote vigorous new growth and strong flowers.
Although the light-scented ‘Grandiflora’ form bears
mostly sterile flowers on a shrub that matures at around 9 feet (3 meters),
there are enough fertile ones mixed in to attract lots of bees. As the flowers age in September and
October, they take on delicious hues of rose and green before turning parchment
brown, often staying on the shrub until spring.
Several new Hydrangea
paniculata cultivars have been introduced recently. ‘Tardiva’ is fall-flowering with loose,
pointed blossoms; ‘Pink Diamond’ is compact at 4 feet (1.3 meters) with large
flower panicles in June and July that turn deep pink with a red reverse in
September; ‘Praecox’ has a mix of sterile and fertile flowers that give it the
appearance of a white lacecap; ‘White Moth’ has long-lasting, rounded
flowerheads composed of sterile flowers.
A new introduction, ‘Grandiflora Unique’, has even bigger flowers than
its parent—not necessarily an improvement, however, since peegee’s flamboyant
blossoms make it hard enough to integrate into a garden design, except as a
specimen plant or as a focal plant in an all-green corner.
Like all hydrangeas, the peegee
makes a lovely addition to a lush, romantic summer bouquet.
Smooth hydrangea (Hydrangea arborescens)
Native to the Eastern U.S. where it was discovered
in 1736, this hydrangea and its various cultivars are now a mainstay of the
design palette for the shade garden.
The species grows from 3-5 feet tall (1-1.7 meters) with dark green
leaves and upright stalks topped with rounded flowers that start off ghostly
green, gradually turning creamy-white, then brown. It is an open, sprawling, yet graceful shrub that lights up the
shadows of deciduous woods in a large area from New York to the midwest and
south to Florida and Louisiana.
To make smooth hydrangea at home in the garden, soil
should be moist, humus-rich and slightly acidic. If the July flowers are deadheaded, a second smaller crop is
possible in late summer. Although a
woodland plant that looks lovely with ferns, hostas and dark green yews, it
will do well in a sunny spot as long as the soil is kept moist. The hardiest of all hydrangeas, it will
over-winter as far north as Zone 2b.
Like peegee hydrangea, smooth hydrangea blooms on new growth, so the
shrub should be cut back hard, almost to the ground, in early spring.
Named cultivars of smooth hydrangea like
‘Grandiflora’ have much bigger, pom-pom flowers than the species. When well-fertilized, the flowers of
‘Annabelle’ can grow to be melon-sized.
While spectacular, they tend to look somewhat overpowering in a mixed
garden where they’re expected to share the stage with others.
Adapted from
an article that appeared originally in Canadian Gardening magazine