...without ruining the garden
I was told recently that the reason my rhododendrons don't
bloom is because we put lights on them for the holidays. They
need total darkness, this
If that's the case it would solve a long standing
mystery but we're seriously doubting it. Lots of people in our
neighborhood go all-out on lights, yet there are rhododendrons in
bloom on our block every spring. We can't say for certain that the
bushes we see bloom are the same ones that we see lit up but we
think they are.
So what's the straight scoop? Okay to light the lights?
- D.S. -
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Does it affect shrubs' bloom, to bear holiday lights? Not in
winter, when flower buds are already set to go for spring. But take
care as you decorate to avoid physically damaging
the plants or garden.
Light the lights! Rhodies don't mind night light.
The decrease in day length as summer wanes does spur
Rhododendrons to form their flower buds but they don't need
such a long night as some species, including poinsettia and
garden mum. They are also less sensitive to nighttime light during
bud formation than some other plants.
By winter, Rhododendron flower buds are set. Then the
plant is indifferent to night lights. At that point, all it needs
is cold (40F or below) for six weeks or more to finish flower
Once the big flower buds are set on a
Rhododendron's branch tips, you can be pretty confident of the
next spring's bloom. By the same token, it's too late by winter to
coax flower buds to form on branches that set only small vegetative
After that, those buds will open after being consistently warm
for at least a few weeks. Early blooming rhodie varieties bloom 3
weeks into spring. Later varieties need more time.
When the plant resumes growth in spring, the big buds open
into flowers while smaller buds become new shoots and leaves. Those
new shoots will be ready to form their own flower buds later that
summer for the next year's show.
It's light-ers, not lights,
that pose potential trouble
When it comes to holiday lights, our worries revolve around
broken branches, girdled trunks and ruined soil:
- Limbs break when people yank wires in a hurry to be done
removing the lights.
- Girdling can happen when cords that encircle branches or trunks
are left in place into the growing season.
- Ruined soil comes from heavy feet on cold wet ground.
As pros at botanical gardens light the landscape, they follow
the same watchwords. (Tips from
Below: Do it, light those lights! But be
These three trees are at risk for breakage, either when the
extra weight of snowy or ice- crusted wires comes to bear on the
thin branches, or when the de-lighting technician gets impatient in
We love the look of a light-encrusted tree but see that the
monumental task of wrapping all those lights leads many people to
say, "Let's just leave them there until next year..." ...a leaving
that sometimes goes on for years. Trunks and branches can increase
significantly in girth each spring, and even a string wound tight
around can girdle the limb, killing everything above the
This tree is a likely candidate for damage due to its
holiday decor. However, most people wouldn't know to link the
tree's later decline to the lighting. Here's the connection: If the
spruce is in a bed -- as it should be since its feeder roots are
concentrated just outside the drip line and do not compete well
with lawn grass -- then the wet, cold soil there can easily be
trampled to root-killing airlessness by lots of circling
and jumping up to poke lights into place.
Now, for things that can quash a
- Too much shade. (Only a few Rhododendron varieties
perform well in full shade, such as those with lots of R.
maximum in their lineage.)
- Nutritional deficiencies. (Often related to high pH; rhodies
need acid/low pH.)
- Harsh winters. (Can freeze-dry the buds; such plants would show
leaf damage, too.)
- Being sheared or having all their branch tips clipped back after
early August. (When too little growing time remains for new shoots
to form flower buds.)
might you clip the branch tips? Some people do it to
remove the visual mess of spent blooms. Do this or other pruning
without qualm as long as it's done within about a month after the
Here we're deadheading a Rhododendron in early July
by snapping off (A) the individual spent flower parts. If we were
short on time and didn't mind the tight-cropped look, we could
shear the whole plant, removing spent blooms and new tips. Buds
such as B, yet to open, still have plenty of time to grow, mature
and set flower buds.
Notice that branches which did not bloom this spring
commenced new shoot growth (C) sooner than the branch that was busy
flowering. That's why branches that bloomed one year may not bloom
as well the next -- they engage in "alternate year bloom" because
new shoots get going too late. Early deadheading might even out the
show on a plant that's stuck in an alternate-year bloom
More on pruning a Rhododendron in What's
Coming Up #86.
Sheared?! You bet, if
that's the look you like.
For proof, just stroll a few traditionally maintained Japanese
gardens to see azaleas flowering even though they are tightly
sheared (azalea is simply the common name for various species of
You might take it to be boxwood, that undulating enclosure
punctuated by Japanese maples. However, it's azaleas, at Portland,
Oregon's lovely Japanese Garden.
We can hear the wails from mid-continental gardeners who
hesitate to clip even one branch, because these plants grow so
reluctantly in their gardens. Yet in favorable environments they
grow vigorously and can indeed be sheared and shaped.
What's favorable? How about on a slope where water's
constantly trickling down toward the stream, in the moist air of Great Smoky Mountains National Park? Yup,
that's a wild Rhododendron Janet's exclaiming over,
putting to shame many a garden variety shrub that bears its
And when we think about it, maybe it's a good thing they
don't grow so large as they could, in front of our homes. Here,
PJM Rhododendrons with serviceberry (Amelanchier
Association of Wayne County, Michigan
Always learning and sharing what they know to help others grow!