PlantPeers
Back to Catalog
No image available
Ericaceae FAMILY Least Concern

Rhododendron arboreum

Rhododendron arboreum

Edibility
2/5
Medicinal
2/5

Safety & Hazards

All parts of the plant (including the leaves, flowers and pollen) contain greater or lesser amounts of the toxic compound andromedotoxin (also known as grayanotoxin) [1, 2, 3, 4]. 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[4].

Cultivation Details

HabitEvergreen Shrub
Growth—

Rhododendron arboreum is moderately cold-hardy, tolerating temperatures down to between -10 and -15°c when fully dormant. The pink flowered form is hardier than the red[5]. 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[6]. Succeeds in most humus rich lime free soils except those of a dry arid nature or heavy or clayey[7]. Prefers a peaty or well-drained sandy loam[7]. Succeeds in sun or shade, the warmer the climate the more shade a plant requires[6]. Requires a pH between 4.5 and 5.5[6]. Succeeds in a woodland though, because of its surface-rooting habit[6], it does not compete well with surface-rooting trees[7]. 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]. There are many named varieties selected for their ornamental value[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]. A very ornamental plant, it is the national flower of Nepal[7, 1, 8]. The flowers are sold in local markets and used as offerings in the temples[8, 3]. Plants in this genus are notably susceptible to honey fungus[6].

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[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[9]. Cuttings of half-ripe wood, August in a frame. Difficult[9]. Cite as: Temperate Plants Database, Ken Fern. temperate.theferns.info. 2026-02-21. <temperate.theferns.info/plant/Rhododendron+arboreum>

Pollinators

Insects

References

  1. [1]Flowers of the Himalayas. — Polunin. O. and Stainton. A. · Oxford Universtiy Press · 1984 · ISBN - ↩︎A very readable and good pocket guide (if you have a very large pocket!) to many of the wild plants in the Himalayas. Gives many examples of plant uses.
  2. [2]Glossary of Indian Medicinal Plants (Including the Supplement). — Chopra. R. N., Nayar. S. L. and Chopra. I. C. · Council of Scientific and Industrial Research, New Delhi. · 1986 · ISBN - ↩︎Very terse details of medicinal uses of plants with a wide range of references and details of research into the plants chemistry. Not for the casual reader.
  3. [3]Rhododendron Species and Their Uses with Special Reference to Himalayas - A Review — Bhattacharyya D. · 2011 · ISBN 0975-2773 ↩︎A useful breif guide to the uses of Rhododendron species in the Himalayas
  4. [4]Grayanotoxin Poisoning: ‘Mad Honey Disease’ and Beyond — Jansen S.A. et al · 2012 · https://doi.org/10.1007/s12012-012-9162-2 ↩︎An in-depth review of the literature on the toxic effects of a toxin widely found in the family Ericaceae
  5. [5]Shrubs. — Phillips. R. & Rix. M. · Pan Books · 1989 · ISBN 0-330-30258-2 ↩︎Excellent photographs and a terse description of 1,900 species and cultivars.
  6. [6]The New RHS Dictionary of Gardening. 1992. — Huxley. A. · MacMillan Press · 1992 · ISBN 0-333-47494-5 ↩︎Excellent and very comprehensive, though it contains a number of silly mistakes. Readable yet also very detailed.
  7. [7]RHS Dictionary of Plants plus Supplement. 1956 — F. Chittendon. · Oxford University Press · 1951 · ISBN - ↩︎Comprehensive listing of species and how to grow them. Somewhat outdated, it has been replaced in 1992 by a new dictionary (see [ 200 ]).
  8. [8]Plants and People of Nepal — Manandhar. N. P. · Timber Press. Oregon. · 2002 · ISBN 0-88192-527-6 ↩︎Excellent book, covering over 1,500 species of useful plants from Nepal together with information on the geography and peoples of Nepal. Good descriptions of the plants with terse notes on their uses.
  9. [9]Propagation of Trees, Shrubs and Conifers. — Sheat. W. G. · MacMillan and Co · 1948 · ISBN - ↩︎A bit dated but a good book on propagation techniques with specific details for a wide range of plants.
  10. [10]A Manual of Indian Timbers. — Gamble. J. S. · Bishen Singh Mahendra Pal Singh · 1972 · ISBN - ↩︎First written in the 19th century, but still a classic, giving a lot of information on the uses and habitats of Indian trees. Not for the casual reader.
  11. [11]Flora of China — Missouri Botanical Garden Press; St. Louis. · 1994 · http://flora.huh.harvard.edu/china/ ↩︎An excellent, comprehensive resource in 25 volumes. In addition to the botanical information the flora also gives basic information on habitat and some uses. An on-line version is also available.
  12. [12]IUCN Red List of Threatened Species — http://www.iucnredlist.org/ ↩︎A list of plants under threat and facing possible extinction, usually with brief details of the threats and information on habitat.
  13. [13]Cornucopia - A Source Book of Edible Plants. — Facciola. S. · Kampong Publications · 1990 · ISBN 0-9628087-0-9 ↩︎Excellent. Contains a very wide range of conventional and unconventional food plants (including tropical) and where they can be obtained (mainly N. American nurseries but also research institutes and a lot of other nurseries from around the world.
  14. [14]Sturtevant's Edible Plants of the World. — Hedrick. U. P. · Dover Publications · 1972 · ISBN 0-486-20459-6 ↩︎Lots of entries, quite a lot of information in most entries and references.
  15. [15]Tanaka's Cyclopedia of Edible Plants of the World. — Tanaka. T. & Nakao S. · Keigaku Publishing; Tokyo · 1976 · ISBN - ↩︎The most comprehensive list of edible plants I've come across. Only the briefest entry for each species, though, and some of the entries are more than a little dubious. Not for the casual reader.
  16. [16]Forest Flora of Chakrata, Dehra Dun and Saharanpur. — Gupta. B. L. · Forest Research Institute Press · 1945 · ISBN - ↩︎A good flora for the middle Himalayan forests, sparsly illustrated. Not really for the casual reader.
  17. [17]Passion Flowers — Vanderplank. J. · Cassell. London. · 1991 · ISBN 0-304-34076-6 ↩︎An excellent book on passion flowers, giving information on hardy species and how to grow the less hardy in greenhouses etc. A bit lacking at times on specific information on hardyness. Excellent photographs.
  18. [18]CosIng — http://ec.europa.eu/growth/tools-databases/cosing/ ↩︎CosIng is the European Commission database for information on cosmetic substances and ingredients.