The enormous genus Rhododendron comprises more than a thousand species. They are naturally distributed on every continent except Antarctica, Africa and South America. The highest concentrations of species occur in the temperate and mountainous regions of China, Japan, Korea and Taiwan. Grown for their showy flowers, rhododendrons are garden favorites worldwide and have been highly hybridized. There are more than 28,000 registered cultivars.
Plants in this genus are extremely variable in size, habit and floral form. Some are tall trees, but most are medium to large shrubs with mounded habits. A few odd species are epiphytes (tree-dwellers). They can be evergreen, deciduous or semi-evergreen. Rhody leaves are arranged alternating on the stem. They can be tiny or large and are usually elliptical or lance-shaped with smooth edges. Leaf surfaces can be smooth, glossy, hairy or scaled.
The flowers are generally borne in clusters, but some have single blooms. They appear at the ends of the branches, a few on lateral shoots. The clusters are called trusses and may have few or many blooms. They may be small or large and funnel-shaped, bell-shaped, tubular, or saucer-shaped, and double, semi-double, or hose-in-hose (one bloom in another) forms exist. Flower color is wide-ranging. The blooming period is dependent on the species or cultivar. Flowers can be produced from late winter to autumn, but most garden types flower from late winter to spring. The fruit is a capsule which splits to expel many small, dark seeds.
Classification is complex. Taxonomists have split the genus into several sub-genera as a result of intensive study, and changes to the nomenclatural status of Rhododendron continue to be made. For most gardeners, Rhododendron can be divided into five general types, large-leaved rhododendrons, small-leaved rhododendrons, vireya rhododendrons, evergreen azaleas and deciduous azaleas.
Rhododendron culture and use is species or cultivar dependent. It is best to match each plantís growth requirements and site needs. Generally, most prefer indirect light and highly organic, acid soil. Most are shallow-rooted and require a combination of good drainage and even soil moisture, hence the need for lots of organic matter. Mulch plants well to conserve moisture and protect their roots. Many types develop buds in the summer for the following spring, so prune them shortly after they flower. Summer pruning can result in poor flowering the following year.
Rhododendron are beautiful in woodland gardens and look best planted in masses, especially in open forests. They are ideal for shaded foundations and borders and pair well with other Ericaceous ornamentals
Botanical Name: Rhododendron 'Advent Klokken'
Common Name: Azalea 'Advent Klokken
Plant Type: Shrub
Flower Color: Violet red
Foliage Color: Green
Best Season: Spring
Height (m): up to 2
Rhododendron 'Advent Klokken'bears double, violet red,
Notes: One of the most
colorful and free flowering of the evergreen shrubs. It's a member of the
Rhododendron genus, but it is much better suited to South African conditions
than its large-leaved, large-flowered cousin.
Azaleas are shade loving and require semi-shade. Morning sun is preferable to
afternoon sun - light filtered shade being ideal. They do particularly well
under deciduous trees, for they welcome the warmth of the sun in winter when
developing their buds, and then as the tree's leaves return the plants are
sheltered from the heat of the blazing sun. In cool, moist conditions, Azaleas
can be grown in sunny positions. Containers do well on patios.
An acid, well-drained humus soil is required with a pH level between 4.5 - 5.5.
Heavy clay soils require improvement. A good rule is to improve the planting
site by using organic matter in the form of well-rotted acid compost, peat moss
(the imported brands are preferable) and leaf mould.
Azaleas can be planted at any time of the year. Prepare a garden bed by digging
in organic matter. This is best done about a week before planting to let the
soil settle down and "mature". Dig the planting hole to twice the
size of the container. Carefully tap out the plant from the container - be
careful not to disturb the root ball and plant it so that it finishes at the
same depth as it was in the original container. Fill the hole around the plant
to half depth and firm down. Water well. Finally backfill with garden soil
mixed with compost and press down firmly.
Soil should be moist at all times but not wet and soggy. Do not over water.
Azaleas are surface rooters and if you water a little and often, it will cause
the roots to come closer to the surface and dry out. It is better to water less
often and deeply. Ample water, is however, an important factor in keeping the
plants happy, particularly when they start making their buds at the end of
autumn and through to the end of their flowering period, as well as in summer
when it is hot and dry. Leaf drop and droopy leaves are usually caused by too
Plant with super phosphate and use again two months after planting. During the
growing season, fertilize with 2:3:2 fertilizer, well rotted kraal manure, or
an organic or seaweed based liquid fertilizer. Regular feeding is vitally
Because of the shallow root system, mulching is essential to stop the plants
from drying out. A light mulch of peat moss, acid compost or well-rotted kraal
manure with leaf mould is beneficial. Well-rotted pine needles can also be
used. Remember not to disturb the soil around the plant due to the shallow root
After flowering, prune undesirable branches and tips. This serves to neaten the
appearance of the bush and encourages a compact, bushy growth habit with
numerous terminal-growing tips. Each one of these will produce a flower bud for
the following spring season. This practice ensures constantly good blooming
performances year after year. Old woody plants will benefit from a severe
pruning during late spring, immediately after flowering. Within a few short
years, the plant would have re-grown into a healthy specimen.
Pest and Disease Control
Azaleas are hardy plants and reasonably free of pests. Red Spider, Thrips and
Lace Bugs are the most common, but can be controlled by using any of a number
of available pesticides. Petal Blight and Black Spot can also be controlled in
If in spite of the acidity of the soil being maintained by applying regular
mulches, the leaves are found to be turning yellow, it usually means there is a
lack of certain trace elements in the soil and the plant should be fed with
Iron Chelate or Trelmix - a trace element mixture. Or else it is being over or
under watered. Too much water generally causes Browning at the tips too
Most Azaleas grow well in containers. The secret is to plant them in good acid
compost and potting mix. Never allow drying out. Don't over water especially in
winter and don't over plant - it will cause root rot. They make a marvelous
show and can be brought indoors at flowering time for closer enjoyment!