Rhododendron japonicum Seeds | Japanese Azalea

Japanese Azalea (Rhododendron japonicum) with funnel-shaped orange-red flowers on a deciduous shrub — Japanese Azalea (*Rhododendron japonicum*): Ericaceae, the deciduous flame azalea of Japanese mountain meadows.

LATIN NAME: Rhododendron japonicum

COMMON NAME: Japanese Azalea

Plant Profile

The Japanese Azalea is a compact, rounded, deciduous shrub that in late spring covers itself in funnel-shaped flowers of a hot orange-red to scarlet, often before the leaves are fully out. Each flower cluster sits at the tip of a shoot like a small bouquet, and the effect on a mature plant of a metre and a half is of a shrub in flame. The mid-green leaves are softly hairy when young, oblong and rather thin for a rhododendron, and they turn coppery before falling.

In the wild it grows in full sun on the mountain meadows and open grasslands of central and northern Honshu, a habitat that sets it apart from the woodland rhododendrons: it wants light, acid, humus-rich ground that never dries completely, and it resents the deep shade most of its evergreen cousins prefer.

Science & Biotechnology

The species has a long role in Japanese horticulture and in the breeding of the deciduous hybrid azaleas that filled European gardens in the twentieth century, with its vivid colours and its sun tolerance passed into the Exbury and Knap Hill lines. Like all rhododendrons it contains grayanotoxins in every part, the compounds behind the famous mad honey produced by bees working rhododendron nectar in the Black Sea region, and the plant is strictly a garden subject, never a kitchen one. Ecological studies of its native meadows have tracked the decline of its habitat as traditional grassland management has lapsed, making wild populations of conservation concern in Japan.

Its flowers are worked heavily by bumblebees, whose timing matches the bloom, and seed-grown plants show useful variation in shade from yellow-orange to deep scarlet.

Uses & Benefits

In the garden it is one of the best deciduous shrubs for acid soil in full sun: a spring spectacle, a good foliage plant through summer and a neat silhouette in winter. It combines naturally with other acid-lovers and, given the meadow origin, it suits an open bank or a birch-and-pine clearing where woodland rhododendrons would sulk.

It needs no pruning beyond the removal of spent heads if tidy seed pods are wanted less than the next season’s flowers. As a species it breeds true enough from seed to be worth raising for the colour variation, which runs from apricot to blood red.

Growing from Seed

Sow the dust-like seed on the surface of an acid, humus-rich seed compost in late winter, watering with a fine spray and keeping the tray under glass at 15 to 20 °C; do not cover the seed, which needs light. Germination takes three to six weeks and the seedlings are minute, so keep them uniformly moist and shaded through the first summer.

Prick out gently with tweezers once each seedling shows two true leaves, grow them on in acid potting mix, and line them out in a shaded nursery bed for two or three years before their final position. Plant out into acid, leafy, free-draining but moisture-holding soil in full sun, and mulch annually with leaf mould or pine needles.

Our Take

A meadow azalea in flame-red, happy in full sun where most rhododendrons demand shade. For acid soil it is the most exciting deciduous shrub of late spring.

Flower Seeds