Practical
Plants

Rhododendron japonicum

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Taxonomy and growth

Family
Ericaceae
Life cycle
perennial
Foliage
deciduous
Woodiness
woody
Height
2 m
Fertility
Insects
Flower type
hermaphrodite
Pollinators
Insects

Uses

Toxicity

Toxicity warning. The historical record reports a hazard for this plant. Do not use it to decide which parts are safe to eat or use medicinally.

Although no specific mention of toxicity has been seen for this species, it belongs to a genus where many members have poisonous leaves. The pollen of many if not all species of rhododendrons is also probably toxic, being said to cause intoxication when eaten in large quantities[5].

Edible uses

Leaves[4]. No more details are given but some caution is advised, see the notes above on toxicity.

Plant part
Leaves

Medicinal uses

Historical medicinal uses. These records describe reported uses. They do not establish safety or effectiveness. Ask a qualified health professional before using any plant medicinally.

Diuretic, tonic[3].

Product or use
Diuretic
Product or use
Tonic

Environment

Range
E. Asia - Japan.
Habitat
Dense woods in mountains in C. and S. Japan, to 1800 metres[2][7].
Light
full sun
Shade tolerance
light shade
Water
moderate
Hardiness
Zone 5+
Soil textures
sandy, loamy
Soil pH
very acid, acid
Drainage
well drained
Tolerates Nutritionally Poor Soil
No
Drought
intolerant

Propagation

Seed - best sown in a greenhouse as soon as it is ripe in the autumn and given artificial light. Alternatively sow the seed in a lightly shaded part of the warm greenhouse in late winter or in a cold greenhouse in April. Surface-sow the seed and do not allow the compost to become dry[6]. Pot up the seedlings when they are large enough to handle and grow on in a greenhouse for at least the first winter. Layering in late July. Takes 15 - 24 months[8]. Cuttings of half-ripe wood, August in a frame. Difficult[8].

Cultivation

Succeeds in a most humus-rich lime-free soils except those of a dry arid nature or those that are heavy or clayey[1]. Prefers a peaty or well-drained sandy loam[1]. Succeeds in sun or shade, the warmer the climate the more shade a plant requires[6]. A pH between 4.5 and 5.5 is ideal[1]. This species is closely related to R. molle and perhaps not distinct from it[6]. Succeeds in a woodland though, because of its surface-rooting habit[6], it does not compete well with surface-rooting trees[1]. Plants need to be kept well weeded, they dislike other plants growing over or into their root system, in particular they grow badly with ground cover plants, herbaceous plants and heathers[6]. Plants form a root ball and are very tolerant of being transplanted, even when quite large, so long as the root ball is kept intact[6]. Plants in this genus are notably susceptible to honey fungus[6].

References

  1. F. Chittendon. RHS Dictionary of Plants plus Supplement. 1956 Oxford University Press 1951-00-00

    ↩1↩2↩3↩4

  2. Bean. W. Trees and Shrubs Hardy in Great Britain. Vol 1 - 4 and Supplement. Murray 1981-00-00

    ↩

  3. Kariyone. T. Atlas of Medicinal Plants.

    ↩

  4. Kunkel. G. Plants for Human Consumption. Koeltz Scientific Books 1984-00-00 ISBN 3874292169

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  5. Facciola. S. Cornucopia - A Source Book of Edible Plants. Kampong Publications 1990-00-00 ISBN 0-9628087-0-9

    ↩

  6. Huxley. A. The New RHS Dictionary of Gardening. 1992. MacMillan Press 1992-00-00 ISBN 0-333-47494-5

    ↩1↩2↩3↩4↩5↩6↩7

  7. Ohwi. G. Flora of Japan. (English translation) Smithsonian Institution 1965-00-00

    ↩

  8. Sheat. W. G. Propagation of Trees, Shrubs and Conifers. MacMillan and Co 1948-00-00

    ↩1↩2

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