Most Rhododendron hybrids have been derived from plants that came from China, Burma and India. In their natural habitat they grow in forest clearings under the dappled shade of tall trees. Their roots develop in the natural debris of fallen leaves, twigs and branches. This natural leaf mold and mulch is very fast draining and acidic from decaying matter. To succeed with Rhododendrons, we must try to duplicate these conditions as best we can.
Use Elemental Sulphur or Ammonium Sulphate (21-0-0) to acidify. Peat moss also helps acidify the soil.
Rhododendrons and their companions need only moderate fertilizing in spring. A scant handful of 4-12-8 sprinkled around the shrub and watered in, with another light application after blooming, is sufficient.
TYPES OF RHODODENDRONS
Lepidote means scaly and most small-leaved rhododendrons fit into this group. The scales appear on the undersides of the leaves and resemble dots. The P.J.M. Hybrids are valued for their handsome fragrant foliage (which changes colour in winter), earlier flowering and improved hardiness.Elepidote means without scales and describes rhododendrons that are evergreen and have large broad leaves. Flowers are usually large, bell-shaped and very showy.
Yakushimanum Rhododendrons are a beautiful family, which originated in Japan. All have the characteristic thick coating of brown ‘yak’ hair on the undersides of their leaves. This ‘fur’ seems to discourage some insect pests, which may attack other varieties. All ‘Yaks’ are very floriferous, compact and very hardy.
Finnish Hybrids are the product of the University of Helsinki, Finland. These have been bred for hardiness and are some of the hardiest rhododendrons available (to Zone 4 and possibly Zone 3 with some protection).
WHERE TO GROW
Rhododendrons are heavy flowering evergreen plants, which enjoy a shaded, sheltered location in your garden.
Choose a site where some sun is available to encourage bud information and compact growth. Shelter from prevailing winds, which desiccate the foliage and provide shade during the hottest part of the day in summer (from noon until 3:00 p.m.). Protect in winter by building a tent of burlap around your rhododendrons and fill the tent with peat moss or oak leaves to act as insulation.
Azaleas are also heavy flowering plants and enjoy sunny or semi-shaded area in your garden. Generally, the deciduous varieties are the hardiest.
Avoid locations, which are too dry as they enjoy lots of moisture as rhododendrons do. Excellent drainage is essential.
PLANTING
Dig a hole 40 – 50 cm deep and fill it with water. If it takes more than 10 or 15 minutes to drain away, the drainage is insufficient. Sometimes the drainage in the planting hole can be improved by digging deeper and breaking through any hard pan.
The soil mix for filling the hole around the plant should be half peat moss and a quarter each composted manure and topsoil.
Use only 5-15-5-plant starter fertilizer the first year. Mulch around the plant to a depth of 10 cm with wood chips or bark to conserve moisture and protect the shallow roots.
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Deadhead Rhododendrons by breaking off the spent flower. Be careful of the buds under the flower.
To increase blooming in rhododendrons, pinch the tips of new growth in the spring
RHODODENDRONS, AZALEAS AND OTHER ACID-LOVING PLANTS IN A RAISED BED
Rather than a single hole for a single plant, try a group of Rhododendrons or similar plants in a raised bed or berm. This will ensure good drainage.
Work over the soil in the area and place the plant at surface level. Then mound around the plants with a soil mixture that has the necessary humus and acidity. Gently slope the mound so that it does not wash away and mulch the entire area..
COMPANION PLANTS THAT PREFER SIMILAR CONDITIONS
Azaleas, Heaths and Heathers
Mountain Laurel (Kalmia), Leucothoe
Pieris (Japanese Andromeda)
Bearberry (Arctostaphylos)
Wintergreen (Gaultheria)
Blueberries
PRUNING AND DEADHEADING
Rhododendron, Pieris and Mountain Laurel are ‘surge growers’. Vigorous young shrubs produce three different surges of new growth from spring to fall and such growth discourages formation of flower buds. Older shrubs make only one surge and flower buds are usually set in July or early August.
Both Deciduous and Evergreen Azaleas are ‘continuous growers’. Azaleas don’t develop side branches once the shoots emerge from the buds set last year. To provoke branching, pinch once or twice early in the growing season.
Do not pinch later than early August, as the plant will then be setting flower buds for next year.
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