Rhodos are MADE FOR THE SHADE
A combination of relatively cool conditions and fairly acidic soils mean that Tasmania is an ideal place for highly-ornamental rhododendrons to thrive, according to gardening guru
The healthiest and most spectacular rhododendron displays I’ve ever seen were in Tasmania. It’s the combination of relatively cool conditions and a fairly acidic soil that appears to do the trick. Around Queenstown, Rosebery and north-western Tasmania, most rhododendrons not only look fantastic at any time of the year, but appear to be resistant to most pests and diseases.
This is certainly due to reliable, yearround rainfalls received in these districts.
These highly-ornamental plants certainly thrive where temperatures remain fairly low.
I remember visiting several outstanding rhododendron gardens high above Hobart at Fern Tree and was astonished to discover a surprising number of very attractive chance seedlings that had germinated in the acidic, fairly impoverished but well-drained soil, common to high-rainfall areas.
Unfortunately these seedlings also included
Rhododendrons can be grown to perfection in all parts of Tasmania, although they struggle in alkaline or coastal soils
a worrying number of purple-flowered R. ponticum, a notoriously aggressive weed species now causing nightmare problems in parts of Britain.
Luckily, rhododendrons can be grown to perfection in all parts of Tasmania, although they struggle in alkaline or coastal soils. That’s because these lovely ornamental plants are not very good at extracting iron from the soil and alkalinity tends to lock it up.
It is why applying lime – or even wood ashes – around rhododendrons is a big blunder. The disorder – lime-induced chlorosis – causes the youngest leaves to turn almost white and weakens growth. This problem can be corrected by supplying iron chelates, a form which can bypass alkalinity.
Most rhodos flower in mid-spring and right now is an ideal time to make a purchase. Early-flowering varieties include
the beautiful, deep rose-red Unknown Warrior which can come into bloom in late winter in some districts.
We can tell if plants will flower this spring by looking at buds now formed at the tips of branches. Flower buds are big, fat, clearly defined and easily identifiable.
Sometimes, when the plants have been kept in heavy shade for too long, flower buds fail to form and are replaced by narrow, pointed, leaf-enclosed growth buds.
Most varieties demand light, dappled shade, preferably with plenty of bright morning sun while others grow strongly in full sunlight. It’s fairly easy to select the right plant for the best position by leafsize. Generally, plants with small leaves tolerate full sunlight, while those with large leaves grow best in shade. Some develop enormous, handsome leaves. Those of R. macabeanum are a dark, glossy green and almost a third of a metre in length. They look magnificent framing the huge, pale yellow flower trusses.
All rhodos have tight, compact root balls allowing very large plants to be planted or transplanted virtually at any time of the year, summer or winter in Tasmania. Even so, late winter is always best because soils will remain moist for many weeks.
All rhododendrons detest clay so when planting, either select a spot where the soil is deep and friable or create low mounds of good potting soil well above any clay. Never make the mistake of planting too deeply because this may bury lower stems, risking the loss of valuable plants through collar rot.
Rhododendrons rarely need pruning, but respond with strong new growth if leggy branches are cut back. The best pruning time is immediately after flowering – usually in late November.
Feeding rhododendrons is best carried out just once a year, preferably in late winter. Sheep or cow manure is ideal when spread generously over the surface around plants. Fresh stable manure is best avoided – it can kill young plants – but well-weathered horse manure collected from paddocks and fully rotted is excellent. Just make sure all manures or mulching materials are kept well away from main stems.