Bengal clock vine (blue trumpet vine) Thunbergia grandiflora
Bengal clock vine (blue trumpet vine) (Thunbergia grandiflora) is an evergreen perennial shrub in the Acanthaceae family, native to India, southern China and Indochina. It grows 6–15 m (20–49 ft) tall and 3–6 m (10–20 ft) wide, wants full sun and moderate water, and is hardy to about 2 °C (36 °F). Space plants about 3 m (10 ft) apart.
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Bengal clock vine (blue trumpet vine) at a glance
| Type | Perennial shrub, evergreen |
|---|---|
| Family | Acanthaceae |
| Mature height | 6–15 m (20–49 ft) |
| Mature spread | 3–6 m (10–20 ft) |
| Spacing | 3 m (10 ft) centre to centre |
| Sun | Full sun, at least 6 h of direct sun a day |
| Water | Moderate; drought tolerance low, waterlogging tolerance none |
| Soil pH | 5.5–7.5 |
| Cold hardiness | About 2 °C (36 °F) once established (roughly USDA zone 10) |
| Heat stress | Likely above about 40 °C (104 °F) |
| Flowering | about 26–52 weeks after planting, for 26–43 weeks |
| Wind tolerance | Low |
| Pollinator value | High |
| Edible | Not grown as food |
| Native to | India, southern China and Indochina |
| Common in gardens of | 🇹🇭 Thailand, 🇮🇳 India, 🇲🇾 Malaysia, 🇸🇬 Singapore, 🇮🇩 Indonesia, 🇵🇭 Philippines, 🇻🇳 Vietnam, 🇦🇺 Australia, 🇺🇸 United States, 🇧🇷 Brazil |
| Invasive in | Australia (Queensland), Hawaii, Florida: check local rules before planting |
Is Bengal clock vine (blue trumpet vine) toxic?
- People: not known to be toxic
- Cats: not known to be toxic
- Dogs: not known to be toxic
Thunbergia is listed as non-toxic to cats and dogs.
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 Bengal clock vine (blue trumpet vine)
No well-documented helpful pairing. Group it with plants that like full sun and moderate water.
Questions about Bengal clock vine (blue trumpet vine)
- How far apart should I plant Bengal clock vine (blue trumpet vine)?
- About 3 m (10 ft) apart, centre to centre. A mature plant spreads 3–6 m (10–20 ft).
- Does Bengal clock vine (blue trumpet vine) need full sun?
- Full sun: at least 6 hours of direct sun a day.
- How much water does Bengal clock vine (blue trumpet vine) need?
- Moderate water. Drought tolerance is low and waterlogging tolerance none.
- How cold-hardy is Bengal clock vine (blue trumpet vine)?
- It tolerates about 2 °C (36 °F) once established, roughly USDA zone 10.
- When does Bengal clock vine (blue trumpet vine) flower?
- About 26–52 weeks after planting, for 26–43 weeks.
- Is Bengal clock vine (blue trumpet vine) poisonous to cats and dogs?
- For cats it is not known to be toxic; for dogs not known to be toxic; for people not known to be toxic. Thunbergia is listed as non-toxic to cats and dogs.
- What grows well with Bengal clock vine (blue trumpet vine)?
- There is no well-documented companion pairing for Bengal clock vine (blue trumpet vine). Group it with plants that like the same sun (full sun) and water (moderate).
Sources and evidence
Evidence grade B (B: extension service or peer-reviewed).
- Flora & Fauna Web, National Parks Board, Singapore
- UF/IFAS Extension tropical and subtropical fruit and landscape publications, University of Florida
- CABI Invasive Species Compendium, CABI
Notes and assumptions
- Sky-blue trumpets hang all year on a rampant twining climber that carpenter bees love; needs a strong pergola and regular cutting back.
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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