Pruning
July |
Prune macrophylla
before Aug 1.
Deadhead after flowers begin to die.
|
March |
Prune Paniculata and
Arborescens at first of month. Cut entire
plant to 6-12" from ground. |
Unnecessary |
Oakleafs and Climbing
Hydrangeas do not need pruning except to reshape.
If so, reshape after bloom. |
Hydrangea macrophylla (along with H. quercifolia) are shrubs
that set buds on old wood. “Old wood” are the
stems that have been on the plant for at least nine months.
Because of this, pruning Hydrangea in early spring with Nandina,
Boxwood, Forsythia and others will remove the buds from the
shrub.
Buds are generally formed from September to November, so
to be safe any pruning should be done before September and
after flowering in mid-summer. This, of course, does not apply
to dead wood. At any time that you see dead branches on the
shrub they can be removed.
It should be noted as well that, with the exception of removing
dead wood, it is not necessary to prune Hydrangea unless you
want to control the size and shape of the plant. In my current
garden I have taken steps to ensure that each Hydrangea I
plant has plenty of room to stretch and grow as it desires.
This makes my pruning efforts much more manageable -- with
my 120+ Hydrangea, I can use all the help I can get.
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Changing
Colors
In Georgia where glorious Azalea thrive with great ease
due to the naturally acidic soil, Hydrangea macrophylla will
almost always flower in shades of blue. Gardeners who have
their heart set on pink flowers will probably have the most
success if they grow their Hydrangea in pots. In this situation
the gardener can control the soil pH. By providing soil that
is more alkaline than acidic, the flowers will show themselves
as more pink than blue. The color change is actually due to
the amount of Aluminum in the soil being made available to
the plant. The more acidic the soil, the more Aluminum is
available and the more blue the flowers become.
Another option for gardeners seeking pink flowers is to add
lime to the soil in which the Hydrangea is planted. For this
I would recommend dolomitic lime, as it contains Manganese
and over-use is less likely to cause toxicity problems with
your plant. Also, it is available at most nurseries. Changing
the pH with lime will require patience from the gardener,
as the affect does not happen over night. Regular and repeated
applications over several years will be required to see a
color change.
If this seems like too much effort, you might try growing
a different Hydrangea species. For example, H. arborescence
offers an attractive flower that usually begins as a shade
of green and opens to a creamy white. H. quercifolia and H.
paniculata are much larger specimens in general. They each
have cultivars that produce panicles of white and/or pink
blooms.
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Propogation
By far, the fastest method for propagating Hydrangea is to
taking cuttings. While this can be done at any time in the
season, I have personally had the best success in spring and
summer. Gardeners each have their own special process for
propagating plants; some with water, some in peat pots, others
in a sand mixture. The following steps have worked for me
time and again:
- Examine the plant for a strong, healthy stem with at
least two sets of leaves.
- Using sharp shears cut the stem on the diagonal about
a ½ inch below the second pair of leaves. Cutting
on the diagonal is a tip I learned from another AHS member.
When you are making several cuttings at one time, cutting
on the diagonal allows you to know which end in up and which
end is down.
- Remove the bottom set of leaves at the node.
- Using sharp shears again, cut off half or more of the
top set of leaves. Make this cut across the width of the
leaf, not the length.
- If the stem is not a new, soft skin stem then I use my
fingernail to shave off the top layer of “skin”
on the bottom of the stem.
- Dip the stem into a rooting hormone and shake off the
excess powder. The rooting solution I have had the most
success with has been Rootone. I order it on the Internet.
- Fill a pot (I use a 4” pot to begin with) with
soil-less potting mixture or the mixture of your choosing.
- Stick a pencil in the mix to form a hole. Then, stick
the stem into the hole and cover with potting mix making
sure to cover the first node (without the leaves) but not
the second node. I use this technique with the pencil so
that the rooting hormone is more likely to remain on the
plant as it is potted.
- Keep the soil moist and in indirect sunlight. In as little
as a week, sometimes two, roots will begin to form out of
the bottom node and new growth will develop on the second
node.
- After about six weeks I repot the cutting in a true potting
mixture in a larger pot until I am ready to plant it outside.
Another tried and true method for propagating Hydrangea
is by layering. Again, there are many approaches to layering.
If I want to layer a plant, I pull down a branch closest to
the ground and pull off the leaves on the nodes closest to
the ground. I then cover the nodes with soil and sit back
and wait.
After a substantial number of roots have grown (sometimes
I wait an entire year for this) I cut the branch from the
mother plant and transplant it to another area.
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Lacking Blooms
The winters in Georgia are typically suitable to the H. macrophylla
so cold hardiness is rarely the cause for a Hydrangea not
blooming here in the South. The three most common reasons
for Hydrangea not blooming in Georgia are spring frosts, dense
shade and improper pruning.
When warm spring days bring out the Dicentra and Hosta, buds
on the Hydrangea are still developing. Spring frosts that
develop after these warm sunny days can damage the newly forming
blooms. An indicator that the cold has harmed your blooms
is if the new leaf growth is rising from the base of the plant
rather than on the existing wood branches.
If your Hydrangea are planted in too dense of shade they
may not bloom, or it may not bloom well. Hydrangea are known
as shade plants, but they prefer a bit of sun. In fact, my
first group of Hydrangea was planted in full sun. I recommend
that if you are going to grow your shrub in full sun that
you begin with a small shrub, allowing it to acclimate while
it is young. In the Georgia climate you may find that the
leaves wilt in the afternoon and that the need for water is
greater, but the flowering will be worth any extra effort.
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Diseases and Pests
Common Diseases:
Botrytis
Botrytis blight, or gray mold, occurs primarily on greenhouse-grown
hydrangea. Outbreaks of this disease can also be seen in the
landscape on hydrangea flower buds and blossoms. In the greenhouse
and landscape plantings, several consecutive days of cloudy,
humid, rainy weather favor the development of Botrytis blight.
All species of hydrangea are susceptible to this disease,
but damage is noted most often on the bigleaf hydrangea.
On hydrangea, symptoms are usually limited to the flower
buds and especially the petals. The small water-soaked spots
seen on the petals quickly expand into reddish brown irregular
blotches. Brightly colored petals quickly fade to a brown,
withered mass that is often covered with the fuzzy gray growth
of the causal fungus Botrytis cinerea. Masses of gray spores
can easily be seen with a hand lens. Leaf spotting can occasionally
be seen where diseased petals or other debris have fallen
on the leaves.
Given favorable environmental conditions, Botrytis blight
can develop overnight. Cool, humid, wet conditions favor the
rapid growth and reproduction of B. cinerea. The optimal temperature
for the onset of Botrytis blight in the greenhouse is approximately
65 degrees F. The causal fungus survives almost indefinitely
in plant debris. Spores produced on debris are easily dispersed
to healthy tissue by wind currents and then quickly germinate.
Normal greenhouse activities such as watering and shipping
will greatly increase the numbers of spores in the air. Flower
petals and other senescing or wounded tissues are most sensitive
to attack by B. cinerea.
In the greenhouse, control of Botrytis blight involves using
a combination of sanitation, cultural practices, and protective
fungicides.
Greenhouse benches and beds should be cleared of debris or
trash from the previous crop before bringing in fresh plant
material. During the production cycle, continue disposing
of diseased plants, spent blooms, and other debris. Treat
wooden surfaces in propagation and production areas with 2
percent copper naphthenate or a similar surface disinfectant.
Do not collect cuttings for propagation from diseased stock.
Also, handle plants carefully to avoid unnecessary wounding
of the leaves or shoots. If plants are irrigated with overhead
sprinklers or by hand with a water breaker, stop watering
early so the foliage dries by evening. Ventilate and heat
incoming air in the evening to drive down the relative humidity
to the point that greenhouse conditions no longer favor spore
germination and infection. Finally, install a plastic film
over production benches to block the UV radiation needed for
spore formation by B. cinerea.
Fungicides will protect hydrangea from Botrytis blight only
if used in combination with good management practices. Start
treatments when the crop is beginning to bloom and continue
until the crop is finished. Fungicides are available for use
as smoke fumigants or foliar sprays. Some foliar-applied fungicides
may leave an objectionable white residue on the leaves. Smoke
fumigants may burn the petals of some floral crops. Some suggested
fungicides and their treatment intervals are listed in Table
4. Additional information concerning Botrytis blight and its
control can be found in Extension publication ANR-753, "Identification
and Control of Botrytis Blight on Floral Crops and Woody Ornamentals."
http://www.aces.edu/pubs/docs/A/ANR-1212/
Powdery Mildew
Hydrangea virus
Pests
-
Spider Mites
-
Rabbits
-
Slugs
-
Nematodes
Other Issues
-
Chlorosis
-
Heat Stroke
-
Damage from cold
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