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.
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