Grierson’s rhododendron Rhododendron griersonianum
Grierson’s rhododendron (Rhododendron griersonianum) is an evergreen perennial shrub in the Ericaceae family, native to Western Yunnan and northern Myanmar. It grows 1.5–2.5 m (4.9–8.2 ft) tall and 1.5–2.5 m (4.9–8.2 ft) wide, wants part sun to part shade and moderate water, and is hardy to about -12 °C (10 °F). Space plants about 1.8 m (5.9 ft) apart.
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Grierson’s rhododendron at a glance
| Type | Perennial shrub, evergreen |
|---|---|
| Family | Ericaceae |
| Mature height | 1.5–2.5 m (4.9–8.2 ft) |
| Mature spread | 1.5–2.5 m (4.9–8.2 ft) |
| Spacing | 1.8 m (5.9 ft) centre to centre |
| Sun | Part sun to part shade, at least 4 h of direct sun a day |
| Water | Moderate; drought tolerance low, waterlogging tolerance none |
| Soil pH | 4.5–6 |
| Cold hardiness | About -12 °C (10 °F) once established (roughly USDA zone 8) |
| Heat stress | Likely above about 30 °C (86 °F) |
| Flowering | from about June for 3–4 weeks (northern hemisphere; later in cold climates, earlier in warm ones) |
| Wind tolerance | Low |
| Pollinator value | Moderate |
| Edible | Not grown as food |
| Native to | Western Yunnan and northern Myanmar |
| Common in gardens of | 🇬🇧 United Kingdom, 🇮🇪 Ireland, 🇳🇿 New Zealand, 🇺🇸 United States |
Is Grierson’s 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 Grierson’s rhododendron
No well-documented helpful pairing. Group it with plants that like part sun to part shade and moderate 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 Grierson’s rhododendron
- How far apart should I plant Grierson’s rhododendron?
- About 1.8 m (5.9 ft) apart, centre to centre. A mature plant spreads 1.5–2.5 m (4.9–8.2 ft).
- Does Grierson’s rhododendron need full sun?
- Part sun to part shade: at least 4 hours of direct sun a day.
- How much water does Grierson’s rhododendron need?
- Moderate water. Drought tolerance is low and waterlogging tolerance none.
- How cold-hardy is Grierson’s rhododendron?
- It tolerates about -12 °C (10 °F) once established, roughly USDA zone 8.
- When does Grierson’s rhododendron flower?
- From about June for 3–4 weeks (northern hemisphere; later in cold climates, earlier in warm ones).
- Is Grierson’s 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 Grierson’s rhododendron?
- There is no well-documented companion pairing for Grierson’s rhododendron. Group it with plants that like the same sun (part sun to part shade) and water (moderate).
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.
- Flowers late, in early summer, with loose trusses of long scarlet trumpets. Found by George Forrest in 1917 and named after R. C. Grierson of the Chinese customs service; it became one of the most used parents of red hybrid rhododendrons, such as ‘Elizabeth’.
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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