Kirishima Azalea – Rhododendron obtusum

Krishima Azalea, or Japanese Azalea as it is sometimes called, is a member of one of the largest genus of cultivated plants — the Rhododendrons. Members of this genus range between tiny evergreen shrubs to large deciduous trees.

The whole Rhododendron genus have one thing in common: they thrive in an acid soil. For this reason, it is important to keep the Kirishima Azalea in a compost that has a low pH of around 5.

The Kirishima Azalea likes a bright position that is out of direct sunlight. During the flowering season it requires a relatively high humidity.

Pot plants are usually sold when they are 25-40cm (10-16in) tall. When they are full grown, plants can reach up as high as 100cm (40in). However, they are slow-growing plants and they take several years to reach full maturity.

The plants have delicate stems that have.leaves along their entire length. The flowers grow between these leaves, often in bunches of three. Flowers can vary in colour from pastel pink to a fiery red. Some even have violet blooms. The flowers are trumpet-shaped.

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The Kirishima Azalea should be kept indoors during the winter but in the summer, when it has finished flowering, it can be placed outdoors where its dark, bushy foliage can be appreciated. If you place a plant on a window ledge, make sure that it is sheltered from the sun’s rays and is out of the line of cold winds.

Through The Year


When the plant blooms in the spring, provide it with plenty of water and humidity. Use only rainwater or distilled water.


After flowering, it can be moved outdoors to a bright, sheltered site. Water regularly and feed two to four times during the summer with an acid-based fertilizer.

Take cuttings in July or August and place them in a peat-based compost. Keep at a temperature of about 21°C (70°F). Cover the cuttings with a polythene bag or sheet until they strike roots.

September—November Move the plant indoors during the autumn and repot if potbound.


Keep at 8°-10°C (45°— 50°F) until buds begin to appear in late February or March. As buds develop, increase watering and move the plant to a warmer location of around 15°C (60°F). Mist spray when blooms appear.

Pests And Diseases

Young leaves that wither at the edges and turn yellow indicate that the plant is anaemic and lacks iron.

Treatment: Correct the composition of the soil by adding a specially formulated Rhododendron fertilizer.

Mouldy patches on the leaves are a sure sign that the plant has been infected by a fungus.

Treatment: Cut away and destroy all affected parts of the plant and treat it with a systemic fungicide. Also increase the ventilation around the plant to avoid this happening again.


With the right care, the Kirishima Azalea can be kept in bloom during the spring for many weeks. If the compost is allowed to dry out, the plant will wilt and the leaves will drop. Pluck off flowers as soon as they begin to fade.

  • Potting: Use a compost made up of coarse peat mixed with leaf-mould and perlite. The compost must be porous and should have a pH of around 5 or 5.5.
  • During the flowering season, water generously from above. Use rainwater or purified water that is soft and tepid. Mist the leaves daily when the plant is blooming. When the plant is resting, keep the compost moist but avoid excess water around the roots.
  • Feeding: Feed two to four times during the season with an acidic-based plant food.


  • Light: This Azalea likes a brightly lit spot that is out of the line of direct sunlight.
  • Temperature: During the winter, keep plants at a temperature of around 10°C (50°F). After they have flowered, place them in a shady spot in the garden or on a window ledge.

Buying Tips

  • Plants are available from nurseries and garden centres from March onwards.
  • Choose a plant that is about 30cm (12in) tall with a few open flowers and a mass of well-developed buds. The flowers and buds should be evenly distributed over the whole plant.
  • It can thrive for many years if well cared for during the summer.

Kirishima Azalea blooms during the spring when its profusion of coral-pink or deeper coloured flowers are a delight. With care, these plants will live for many years.

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