Common Name: Korean Rhododendron

General Information

Rhododendron mucronulatum is a dense, much-branched, upright, deciduous shrub that can grow up to 2.5 metres tall and as much wide[, ].
The plant is harvested from the wild for local use as a food and for use in commercial cosmetic preparations. The flowers are sold for food use in local markets in Korea[]. The plant is often grown as an ornamental, valued particularly for its late winter floral display.

Known Hazards

Although no specific mention of toxicity has been seen for this species, all parts of Rhododendron species (including the leaves, flowers and pollen) contain greater or lesser amounts of the toxic compound andromedotoxin (also known as grayanotoxin). Rarely lethal to humans (and used medicinally in some herbal disciplines), this compound causes dose-dependant overstimulation of the central nervous system with symptoms including various cardiovascular effects (mainly low blood pressure and cardiac rhythm disorders); nausea and vomiting; and a change in consciousness. The effects commence shortly after ingestion and last around two days. These effects are also transferred to honey made from the nectar of the flowers. In some parts of the world bees are used to deliberately produce a honey rich in andromedotoxin which is then eaten for its supposed medicinal, hallucinogenic and aphrodisiac effects.
In contrast to humans, many other creatures are more susceptible to the toxin and it has sometimes proved lethal to grazing animals and household pets. Some forms of honeybees are also killed by the toxin (resistant forms of the bee are used for honey production). Bumblebees are not affected, however, and are also more efficient in pollinating rhododendron flowers, so one theory is that the toxin is produced by the plant in order to favour the bumblebee and improve fertilization rates[].

Botanical References

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Range

E. Asia - Mongolia, northern China, Russian Far East, Japan, Korea

Habitat

Thin woods and open country, especially on volcanic soils[]. Betula or Larix forests, forest margins[].

Properties

Edibility Rating
Other Uses Rating
Habit	Deciduous Shrub
Height	2.00 m
Pollinators	Insects
Cultivation Status	Ornamental, Wild

Cultivation Details

Rhododendron mucronulatum is a very cold-hardy plant, able to tolerate temperatures down to around -25°c when fully dormant[]. Although cold-tolerant when dormant, the flowers and young growth of Rhododendrons are very susceptible to damage by late frosts in regions where these are likely to occur after new growth has commenced in the spring[].
Succeeds in a most humus-rich lime-free soils except those of a dry arid nature or those that are heavy or clayey[]. Prefers a peaty or well-drained sandy loam[]. Succeeds in sun or shade, the warmer the climate the more shade a plant requires[]. A pH between 4.5 and 5.5 is ideal[].
A very ornamental plant[].
Succeeds in a woodland though, because of its surface-rooting habit[], it does not compete well with surface-rooting trees[]. 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[].
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[].
Plants in this genus are notably susceptible to honey fungus[].

Edible Uses

Flower petals - raw[]. Used for making wine and for decorationg rice cakes in Korea[]. Some caution is advised, see the notes above on toxicity.

Medicinal

None known

Other Uses

An extract of the flowers is used as an ingredient in commercial cosmetic preparations as an antioxidant, astringent, emollient, skin conditioner and protector[].

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 mid spring. Surface-sow the seed and do not allow the compost to become dry[]. 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[].
Cuttings of half-ripe wood, August in a frame. Difficult[].