Rhododendron Rhododendron
Rhododendron (Rhododendron) is an evergreen perennial shrub in the Ericaceae family. It grows 1–3 m (3.3–10 ft) tall and 1–2.5 m (3.3–8.2 ft) wide, wants part sun to part shade and moderate water, and is hardy to about -25 °C (-13 °F). Space plants about 1.8 m (5.9 ft) apart.
Plan Rhododendron in your garden →
Free. Draw your beds, then watch it grow through the year in 2D and 3D.
Rhododendron at a glance
| Type | Perennial shrub, evergreen |
|---|---|
| Family | Ericaceae |
| Mature height | 1–3 m (3.3–10 ft) |
| Mature spread | 1–2.5 m (3.3–8.2 ft) |
| Spacing | 1.8 m (5.9 ft) centre to centre |
| Sun | Part sun to part shade, at least 3 h of direct sun a day |
| Water | Moderate; drought tolerance none, waterlogging tolerance none |
| Cold hardiness | About -25 °C (-13 °F) once established (roughly USDA zone 5) |
| Heat stress | Likely above about 30 °C (86 °F) |
| Flowering | from about April for 3–6 weeks (northern hemisphere; later in cold climates, earlier in warm ones) |
| Wind tolerance | None |
| Pollinator value | Moderate |
| Edible | Not grown as food |
| Common in gardens of | 🇬🇧 United Kingdom, 🇩🇪 Germany, 🇯🇵 Japan, 🇨🇳 China, 🇺🇸 United States, 🇳🇴 Norway, 🇰🇷 South Korea, 🇮🇪 Ireland |
Is Rhododendron toxic?
- People: moderately toxic
- Cats: severely toxic
- Dogs: severely toxic
- Parts: all parts, nectar
Grayanotoxins in all parts cause vomiting, weakness and heart effects.
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 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
- avoid With Black walnut: Black walnut releases juglone from roots, leaves and hulls, which is documented to injure or kill this sensitive species. Evidence B
- 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
See Rhododendron in a botanical garden
It grows in these sample gardens, which you can walk through in 3D:
- UC Botanical Garden, Berkeley (10 plants)
- The Butchart Gardens (10 plants)
- Arctic-Alpine Botanic Garden (6 plants)
- Monet’s gardens at Giverny (14 plants)
- New York Botanical Garden (6 plants)
- Jardin botanique de Montréal (10 plants)
- Kew: glasshouses and rock garden (1 plants)
Questions about Rhododendron
- How far apart should I plant Rhododendron?
- About 1.8 m (5.9 ft) apart, centre to centre. A mature plant spreads 1–2.5 m (3.3–8.2 ft).
- Does Rhododendron need full sun?
- Part sun to part shade: at least 3 hours of direct sun a day.
- How much water does Rhododendron need?
- Moderate water. Drought tolerance is none and waterlogging tolerance none.
- How cold-hardy is Rhododendron?
- It tolerates about -25 °C (-13 °F) once established, roughly USDA zone 5.
- When does Rhododendron flower?
- From about April for 3–6 weeks (northern hemisphere; later in cold climates, earlier in warm ones).
- Is Rhododendron poisonous to cats and dogs?
- For cats it is severely toxic; for dogs severely toxic; for people moderately toxic. Grayanotoxins in all parts cause vomiting, weakness and heart effects.
- What grows well with Rhododendron?
- There is no well-documented companion pairing for Rhododendron. Group it with plants that like the same sun (part sun to part shade) and water (moderate).
Sources and evidence
Evidence grade C (C: plausible, mixed evidence).
- ASPCA Toxic and Non-Toxic Plant List, ASPCA
- FAO Irrigation and Drainage Paper 56 — Crop Evapotranspiration, FAO
- RHS Plant Finder, Royal Horticultural Society
- University extension gardening guides (general), Various land-grant university extensions
Notes and assumptions
- Typical garden-cultivar values; varieties differ.
- Needs acidic, well-drained soil.
Reference values for planning, not horticultural, veterinary or medical advice. Varieties, soils and local climates differ: check with a local nursery or extension service.
Related plants
- Blueberry Vaccinium corymbosum
- American cranberry Vaccinium macrocarpon
- Lingonberry Vaccinium vitis-idaea
- Bilberry Vaccinium myrtillus
- Satsuki azalea Rhododendron indicum
- Japanese andromeda (pieris) Pieris japonica
- Heather (ling) Calluna vulgaris
- Mountain laurel Kalmia latifolia