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Rhododendron

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  • Indoor Plants
Rhododendron 'Spicy Lights'
Photo: Jardin botanique de Montréal (Gilles Delisle)

Onglets

Botany

Origin and description

Azaleas, once known as genus Azalea, are now included in genus Rhododendron, although most people usually consider rhododendrons and azaleas to form two separate groups. In this case, the name azalea is usually applied to small rhododendrons with small leaves and small five-stamened flowers that are often grown as indoor plants. The name azalea includes several species and numerous hybrids. They are sold as potted flowering plants and rarely grow to more than 50 cm indoors. The many cultivars have single, semi-double or double blooms in shades of white, pink, red and salmon. The flowers appear from December to May depending on the cultivar (early, mid-season or late).

Species, cultivars and related plants

Azaleas are often sold as Azalea indica or Rhododendron indicum. Rhododendron x obtusum (kurume azaleas) are very compact, bushy hybrids. The stems are covered in fine brown hairs. The Rhododendron simsii (Indian azalea) species has been used to create many large-flowered or double-flowering hybrids. The flowers are grouped at the tips of the stems.

Toxicity

Careful, this plant is toxic. Keep it out of the reach of children and pets.

Common name

Rhododendron / Azalea

Latin name (genus)

Rhododendron cvs.

French common name

Botanical family

  • Ericaceae
Horticulture

Growing conditions

Azaleas like cool temperatures and bright indirect sunlight, especially during the blooming period. It is best to place the plant near an east- or west-facing window. An azalea that is already in bloom when purchased should be placed in a cool room (about 16ºC) out of direct sunlight. In these conditions, the blooms may last for four to six weeks. Starting in June, after all risk of spring frost is past, you can move the plant outdoors, to a partially shaded spot, but it must never lack water. Bring it indoors before any risk of frost and give it nighttime temperatures ranging from 10 to 15ºC for four to six weeks to encourage it to bloom the next spring. To keep relative humidity high, you can set the pot on a saucer filled with gravel and water, being careful not to let the base of the pot sit in the water.

Easy to grow?

Azaleas are difficult to grow because they do not like high temperatures and dry air. They also need a period with cool temperatures to stimulate the blooming period.

Watering and fertilizer

Avoid using hard water on azaleas. If your tap water is hard, use rainwater or distilled water instead. When the plant is in bloom, the soil should be kept moist but not drenched. Never leave water standing in the saucer. After the plant has finished blooming, let the top few centimetres of soil dry out between waterings, but never let the roots get completely dry. Fertilize with an acidifying fertilizer, like rhododendron and azalea food, every other week from April to October. Moisten the soil before feeding to avoid burning the roots.

Pruning and maintenance

Remove faded blooms. After the plant has finished blooming, pinch back the new shoots to encourage the formation of lateral stems. Prune if necessary to keep the plant’s shape and remove any dried stems. Cut back to just above a bud. The plant should not be pruned after early July, because flower buds are initiated starting in August.

Repotting

Repot the plant every two or three years after it has finished blooming. Use a well-drained, acidic potting mix without horticultural lime – for instance, three parts peat moss to one part perlite. Because azaleas have shallow roots, it is best to use wide, shallow pots (called azalea pots).

Propagation

Pests and diseases
  • Cyclamen mites
  • Root rot
Physiological disorders

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