Big-leaf rhododendron Rhododendron sinogrande
Big-leaf rhododendron (Rhododendron sinogrande) is an evergreen perennial shrub in the Ericaceae family, native to Yunnan, south-east Tibet and northern Myanmar. It grows 5–10 m (16–33 ft) tall and 4–8 m (13–26 ft) wide, wants part sun to part shade and high water, and is hardy to about -10 °C (14 °F). Space plants about 6 m (20 ft) apart.
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Big-leaf rhododendron at a glance
| Type | Perennial shrub, evergreen |
|---|---|
| Family | Ericaceae |
| Mature height | 5–10 m (16–33 ft) |
| Mature spread | 4–8 m (13–26 ft) |
| Spacing | 6 m (20 ft) centre to centre |
| Sun | Part sun to part shade, at least 3 h of direct sun a day |
| Water | High; drought tolerance none, waterlogging tolerance none |
| Soil pH | 4.5–6 |
| Cold hardiness | About -10 °C (14 °F) once established (roughly USDA zone 8) |
| Heat stress | Likely above about 28 °C (82 °F) |
| Flowering | from about April for 2–4 weeks (northern hemisphere; later in cold climates, earlier in warm ones) |
| Wind tolerance | None |
| Pollinator value | Moderate |
| Edible | Not grown as food |
| Native to | Yunnan, south-east Tibet and northern Myanmar |
| Common in gardens of | 🇬🇧 United Kingdom, 🇮🇪 Ireland, 🇳🇿 New Zealand, 🇺🇸 United States |
Is Big-leaf rhododendron toxic?
- People: moderately toxic
- Cats: severely toxic
- Dogs: severely toxic
- Parts: leaves, flowers, nectar (honey)
All rhododendrons contain grayanotoxins: eating leaves or flowers causes vomiting, drooling, weakness and heart problems in pets and livestock; honey from some species ("mad honey") poisons people.
If a child or pet may have eaten part of a plant, call a poison centre or vet straight away.
Companion planting: what to grow with Big-leaf rhododendron
No well-documented helpful pairing. Group it with plants that like part sun to part shade and high water.
Keep apart or take care
- caution With Mountain laurel: Mountain laurel and rhododendrons are hosts of Phytophthora ramorum (sudden oak death), which spreads from infected foliage between neighbouring plants. Evidence B
- caution With English lavender: Acid-loving plants need pH 4.5–5.5, lavender prefers neutral to alkaline soil; one bed cannot suit both. Evidence B
Questions about Big-leaf rhododendron
- How far apart should I plant Big-leaf rhododendron?
- About 6 m (20 ft) apart, centre to centre. A mature plant spreads 4–8 m (13–26 ft).
- Does Big-leaf rhododendron need full sun?
- Part sun to part shade: at least 3 hours of direct sun a day.
- How much water does Big-leaf rhododendron need?
- High water. Drought tolerance is none and waterlogging tolerance none.
- How cold-hardy is Big-leaf rhododendron?
- It tolerates about -10 °C (14 °F) once established, roughly USDA zone 8.
- When does Big-leaf rhododendron flower?
- From about April for 2–4 weeks (northern hemisphere; later in cold climates, earlier in warm ones).
- Is Big-leaf rhododendron poisonous to cats and dogs?
- For cats it is severely toxic; for dogs severely toxic; for people moderately toxic. All rhododendrons contain grayanotoxins: eating leaves or flowers causes vomiting, drooling, weakness and heart problems in pets and livestock; honey from some species ("mad honey") poisons people.
- What grows well with Big-leaf rhododendron?
- There is no well-documented companion pairing for Big-leaf rhododendron. Group it with plants that like the same sun (part sun to part shade) and water (high).
Sources and evidence
Evidence grade A (A: strong evidence).
- Plants of the World Online (taxonomy, native range), Royal Botanic Gardens, Kew
- Flora of China, Missouri Botanical Garden & Harvard University Herbaria (eFloras)
- RHS Find a Plant (plant profiles and growing guides), Royal Horticultural Society
Notes and assumptions
- A plant of the cool, misty Himalayan and west Chinese mountains: it wants moist, humus-rich soil and shelter from hot sun and drying wind, and sulks in hot, humid summers.
- Needs acid, lime-free soil (like other rhododendrons and camellias): in chalky ground grow it in a large pot of ericaceous compost.
- Has the largest leaves of any rhododendron, often 60–80 cm long, glossy above and silvery beneath, with big trusses of creamy-yellow bells. Introduced by George Forrest about 1913. It needs shelter from wind and a mild, humid climate, such as the gardens of western Scotland, Ireland and Cornwall.
Reference values for planning, not horticultural, veterinary or medical advice. Varieties, soils and local climates differ: check with a local nursery or extension service.
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