All the colours of the rainbow
THE rhododendron genus is enormous. It includes azaleas, the sub- tropical vireya and hardy deciduous mollis and Knap Hill hybrids.
Flower colours cover almost the complete spectrum with only a true blue a rarity.
They can be planted or transplanted at any time of the year. The best time to buy plants is mid- spring when most are in flower.
Some have big leaves, which means they need part shade, others with small leaves prefer full sun.
Most thrive in open woodland conditions. Deciduous trees without greedy, competitive roots provide perfect, dappled shade. Eucalypts are among the few evergreens suitable for under- planting with rhododendrons.
Some small, compact rhododendrons make excellent rock garden plants in full sun. Their tiny leaves allow them to blend in perfectly with lichen- covered rocks and alpine plants.
All rhododendrons have compact root- balls so are suitable for growing in large pots, urns or tubs. Buy good quality, acidic potting soil.
Add pulverised but coarse coir ( coco- peat) to increase bulk by 20 per cent.
The soil from fully decayed autumn leaves or rotted pine needles are wonderful additives.
Avoid artificial, chemical fertilisers. Sheep manure is perfect. During hot weather, all potted rhododendrons need to be watered twice daily.
When potting soils start to dry out, rhododendron root- balls become waterrepellent so attempts at irrigation fail because the water flows to waste through drainage holes. Drying out is the most common cause of failure with rhododendrons growing in containers.
Even large rhododendrons can be safely moved and the only risky time is immediately after flowering when young fragile shoots may be snapped off.
Almost all rhododendrons are lime- haters so demand an acidic soil.
These plants are not particularly good at getting iron from the soil because of the special way they take up nutrients.
When soil is alkaline or has been limed, the effect is to lock up iron. Most other plants can overcome this, but not rhododendrons.
The youngest leaves display iron deficiency by turning pale while leaf veins stand out clear and green.
This is “lime induced chlorosis” and is a familiar sight in gardens where builders’ rubble has been dumped, or near walls in which lime mortar has been used. Wood ash is highly alkaline and causes the same problem as lime.
Iron chelates have been used successfully to overcome this disorder. It can be found at most garden centres and, after being diluted with water, it is sprayed over and around rhododendrons displaying an iron deficiency.
Many small or thick leaved rhododendrons are able to grow with few problems even where strong winds blow.
It’s the thick, felt- like layer beneath the leaves that stops them from losing moisture.
Many species and CV’s have this protective
layer which is a pale fawn or buff colour and is very much part of the attraction of these special plants.
R. degronianum is one heavily felted species that is much sought after by collectors and admirers.
Most popular rhododendrons have ancestors that originate from western China and the Himalayan region. Flowers are usually in compact or loose trusses. Some are like clusters of glistening waxy bells, as with R. Winsome which is happy growing in full sun.
Other sun lovers include white pearl and the spectacular pink pearl, both of which can grow to the size of small trees.
There are a number of yellow or cream varieties. Unique prefers part shade and almost glows when in bloom.
R. fragrantissima is so heavily fragrant the cut flowers can dominate even a large room.
When flowering trusses wither they are best snapped off at the neck. This stops seed capsules from forming and ensures stronger growth for an even better flowering next spring.
Rhododendrons grow best with plants that like the same acidic soil and growing conditions. Tree ferns, liliums, daphne, Solomon’s Seal, pieris, hellebores, Japanese maples and other woodland plants all make ideal companions.