Questions and Answers on Successfully Growing Rhododendrons
Growing Rhododendrons is quite frustrating for
many folks. Here's the deal in a nutshell.
There are two kinds of these plants - the broadleaf (keep their leaves
all winter) and the deciduous (drop their leaves). In general, the
deciduous ones are hardier than the broadleaf.
Let me note that Azalea and Rhodendron are now lumped together as one
plant rather than being separated in botanical classification.
They all prefer acidic soils. This means that the soil the roots are in
(twice the width of the plant) should be acidic.
Too many gardeners expect to toss a little acidic fertilizer on the
plants and have the plants thrive. This will work in the short term but
in the longer term, an unhappy plant will simply slowly fade away over
The solution is to acidify the entire bed using sulphur and peat moss
as acidifying agents. And to monitor this acidity levels (somewhere
down around 5.0 is good) on a yearly basis as the soil will tend to
return to the acidity level of the surrounding soil.
There is some work that suggests that applying compost tea (made from a
high quality compost and including leaf debris/mold) will enable
rhododendrons to survive in regular soils. The bacteria added enable
the plants to feed. I have not done this so can't really comment on how
accurate it is but it is likely worth a try if you're having troubles.
The most common species sold in garden shops is R. catawbiense and its
hybrids so the following information is aimed at the general gardener
and this plant.
In general, the plant is bud hardy to -15F.
Some cultivars are hardier to lower temperaturs than this. So if your
plant isn't blooming, and the winter temperatures got lower than this,
you know the buds were frozen off.
Now plant hardiness is slightly colder than that with plants themselves
surviving down into USDA zone 4. A hardier plant is 'Northern Lights' -
this is a deciduous hybrid that is bud and plant hardy down to -45F.
I've grown these fragrant flowering plants and they are very good
plants for beginning gardeners (and this advanced gardener too I note)
Here's where a lot of gardeners get themselves in trouble. This plant
does not like full *winter* sunshine.
When exposed to the hot sun during winter months, the broad leaf
species leaves warm up and then the stomata (sweat cells) open up
allowing the leaf to lose moisture. The roots are in frozen ground so
they are unable to replace this lost moisture.
The leaf browns off because of moisture loss.
Excessive wind will create a similar situation but the end result of
both is a browning of the leaf edges or a complete browning of exposed
The plant will survive summer sunshine better than winter sunshine.
The ideal place is a location where the rhododendron is protected from
the noon sun throughout the year.
Questions & Answers
What do I feed my Rhododendron?
Compost. This is a woody plant - no more and no less - and it responds
like any other woody plant to food. As long as you have the soil
acidity right, then compost is an ideal food.
My Rhododendron has brown leaves, will it live?
See the above note re sunshine location. Will it live? Darned if I
know. Some times a plant can be defoliated two or three times and it
will survive. Some times it only takes once. But as long as the stems
aren't brittle and there's green under the tender bark (scratch with
your thumb) then there's hope.
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How do I propagate my plant?
Seeds work well for the most part. Cuttings are tricky; you're going to
need rooting hormone, bottom heat, mist systems and 2-4 months from an
August semi-hardwood cutting to get them to root up properly. You can
try a spring softwood cutting but these are not usually reliable. If
you're a home gardener, go with seed from your own plant.
What's the hardiest variety?
'Northern Lights' and they come in shades of orange and yellow and the
flowers are sweetly fragrant. I grew this plant in my old garden (this
new garden is on limestone so I rather doubt I'll be able to get the
acidity necessary) and I loved it.
I got an azalea for Mother's Day -will it live outside?
These are florists azalea and are not considered hardy unless you live
in a USDA zone 8 or so. Very tender plant but you can try. :-)
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