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University
of Rhode Island GreenShare Factsheets
Hydrangeas
for the Home Landscape
Hydrangeas are workhorses in the garden. They produce sumptuous
petals of color to add beauty to your garden. But they need not
be forgotten once their flowers have died. Hydrangeas can be
captured easily in dried flower arrangements, providing the last
gasp of the summer garden. Pick the blooms on a clear dry day
in late summer and hang to dry. H. macrophylla and H.
paniculata 'Grandiflora' are especially good for drying.
Most species of hydrangeas can be grown in either full sun
or partial shade. They are resistant to most insects and diseases.
They can be grown in a wide range of soil but prefer a rich,
moist soil and should be planted where watering will not be a
problem. Avoid dry windy sites, as their large, soft leaves lose
water quickly, especially on hot, windy days, causing the foliage
to wilt.
Flowers are produced on the new growth; therefore, it is
important that hydrangeas be given some care each season to ensure
that vigorous new growth occurs. Irrigate plants weekly to replace
moisture loss. Prune flower stems after they have bloomed.
Fertilize hydrangeas in early spring with a complete granular
fertilizer at the rate of 2 pounds per one hundred square feet.
Apply fertilizer as broadcast top dressing. During long periods
of drought, water thoroughly each week.
There are many different types of hydrangeas; many require
different methods of pruning. First, one must know the identity
of the hydrangea in the landscape, so the proper pruning procedure
can be implemented.
Hydrangea arborescens 'Grandiflora' -- Hills-of-Snow
Hydrangea
Prune hills-of-snow hydrangea to the ground line each winter
or early spring because it flowers abundantly on new growth, and
is frequently killed back during winter. If a larger shrub is desired
(3+ feet) and/or it is not killed back over the winter, prune less
severely. Remove certain branches to the ground; cut others back
at varying heights from 1 to 3 feet.
Hydrangea paniculata 'Grandiflora' -- Pee Gee
Hydrangea
This is the most commonly planted hydrangea because
of its massive displays of large white flowers in mid-to-late summer.
They gradually turn to pink and remain on the plant in a semi-dried
condition long after the leaves have fallen. Pruning involves the
removal of dead flowers, if unattractive, and an annual corrective
pruning of vigorous shoots. Thin and/or cut back the previous season's
growth in late winter or early spring, since flower clusters occur
on newly developing branches. Without regular pruning, this hydrangea
can rapidly become quite overgrown and out of scale in the landscape.
It can, however, be developed into a single or multi-stemmed tree
form.
Hydrangea macrophylla -- Hortensia or Florist
Hydrangea
This is a commonly grown hydrangea with large globe-shaped flowers. It is frequently
forced by florists and sold as an indoor pot plant during the spring season.
Once moved outdoors, however, color is dependent upon the pH of the soil in
which it is grown: blue if acid; pink if alkaline. There are also several white-flowered
cultivars. Pruning can be accomplished at two different times. Late summer
is more desirable, since most hortensia types flower only from the end buds
of upright or lateral shoots produced during late summer and fall of the previous
season. Prune as soon as the flowers have faded and strong shoots are developing
from the lower parts of the stems and crown. Remove at the base some of the
weaker shoots that are both old and new. Always try to keep several stems of
old productive wood, with a sufficient number of stout new stems that will
flower the following season. Early spring pruning (March), although acceptable,
will result in the sacrificing of bloom for that growing season.
Pruning this species too late in the fall (after September)
is harmful. New growth, both vegetative and reproductive, will
not develop proper maturity. Hortensia is a good seashore shrub;
flowering is more profuse in an open, sunny location. This, however,
increases its vulnerability to bud killing. Winter protection
of the plant should be initiated in December to preserve buds
for next year's flowering. Tie the shoots together and wrap with
burlap. If left unprotected, delay any spring pruning until the
buds swell in order to determine which wood needs to be removed,
and then cut back to below the point of injury.
Hydrangea quercifolia --Oakleaf Hydrangea This
plant is grown primarily for its handsome oak leaf-shaped foliage,
excellent fall color, attractive flowers and interesting winter
bark. It is ideally suited to a lightly shaded or protected location,
and if grown in an exposed site, it is subject to some winter
dieback. Prune back in early spring to remove dead wood. Cut
back to below the point of injury and remove old wood to the
base.
Hydrangea anomala petiolaris -- Climbing Hydrangea Climbing
hydrangea is a desirable mid-summer flowering woody vine that
attaches itself by aerial roots to brick, masonry or wood. It
requires little or no pruning. If certain shoots have grown out
of bounds, reduce their length in summer. Frequently, concern
is expressed about climbing vines that may be inundating a tree
and causing irreparable damage. There has never been a proven
case of damage occurring from climbing hydrangea, however.
The color of the pink and blue varieties is determined by
the degree of soil acidity. Pink varieties develop color best
in the greenhouse at a soil pH of 6.5 to 7.0., while the best
blue color occurs at pH 5.0 to 5.5.
The hydrangea flower is small and insignificant but is surrounded
by showy bracts. The anthocyanin pigment will be pink or blue,
depending upon the incorporation of either iron or aluminum in
its molecules. Insufficient aluminum is absorbed by the plant
at a pH of 6.5 to 7.0 so iron is used.
As the pH drops to 5.0 to 5.5, aluminum becomes more soluble,
is absorbed by the plant and becomes part of the anthocyanin
molecule resulting in blue coloration.
White hydrangeas contain no pigment in their sepals (although
some may develop as the blossom ages). They may be grown as either
pink or blue, the only indication being given by the small petals.
Common white varieties are Sister Therese and Regula. Rose Supreme,
Merritt's Supreme and Merveille are examples of varieties which
can be blue or pink depending on soil conditions.
To maintain pink coloration, enough limestone should be
incorporated in the soil at the time of planting to keep the
pH at the above levels.
The aluminum necessary for blue color will become soluble
in nearly any soil at a pH of 5.0 to 5.5. Depressing the pH with
aluminum sulfate will also supply soluble aluminum. Since soluble
phosphates precipitate aluminum, a fertilizer containing low
phosphorous or none at all should be used (13-0-20 and 15-0-15
are examples).
While these methods of changing the flower color can be
used, it's not a wise idea to do it indefinately. You risk severely
altering the soil pH thereby making it difficult for the plant
to utilize nutrients. Always get the soil tested before altering
it. Refer to GreenShare Factsheet on
soil testing for more information. If you really like different
colors in your hydrangeas then get many different cultivars!
If you obtain a potted hydrangea for Easter or Mother's
Day in full bloom, keep the soil moist at all times as this plant
has a high water requirement and tends to dry rapidly in the
home. It should also receive direct light.
After the flowers fade, they may be removed and the plant
treated as a house plant. When danger of frost is past, it can
be planted in a sheltered location in the garden. Shelter is
necessary because the hardiness of this plant is questionable
in our northern gardens. This plant forms flower buds in the
fall like forsythia and dogwood. It is these buds which freeze
out or are destroyed in colder climates. Many times the plant
will survive and produce green leaves, but no flowers. Planting
in a sheltered location plus covering the plant with burlap will
offer some protection. If you wish to improve the probability
of flower bud survival, you may wish to try this.
When danger of frost is past, plant in a sheltered place
in the garden. On the 4th of July, prune to 3 to 5 inches from
the ground. The plant will produce short branches terminating
in a dormant flower bud. Before the temperature falls to 25 degrees
F, place a screen around the plant. Fill this with an insulating
material such as coarse peat moss, vermiculite or bark. More
material may be added if it settles during the winter. Remove
this protection when the crocuses flower but protect on cold
nights. If you are lucky, the flower buds will survive. In any
event, you should have a pretty foliage plant.
If you are successful in over-wintering
these varieties, fertilize with your usual garden fertilizer
(such as 5-10-10).
If you desire blue flowers, have your soil tested as a low pH
is needed. 'Nikko Blue' is a common true blue variety. To lower
the pH, apply aluminum sulfate or sulfur. Avoid over acidification
and "playing" with the soil chemistry and plants. For pink flowers,
limestone may be necessary to raise the pH since soils are naturally
acidic in Southern New England. Always choose varieties for the
colors you like.
If you are not successful in over wintering greenhouse varieties,
hardy hydrangeas are available. Some are: Hills of Snow Hydrangea (H.
arborescens Grandiflora, similar to the greenhouse
varieties), Pee Gee Hydrangea (H. paniculata Grandiflora) or
Climbing Hydrangea (H. anomala petiolaris).
Adapted by Rosanne Sherry,
URI Master Gardener Coordinator, 7-98
Based on fact sheets from Cornell-Suffolk Co. Long Island New York Cooperative
Extension, Connecticut Cooperative Extension and Virginia Cooperative Extension.
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are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
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When trade names are used for identification, no product endorsement
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Be sure that the pesticide you intend to use is registered for
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The user of this information assumes all risk for personal injury
or property damage.
For more
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
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of Rhode Island Cooperative Extension provides equal program
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