Great blue lobelia Lobelia siphilitica
Great blue lobelia (Lobelia siphilitica) is a deciduous perennial flowering plant in the Campanulaceae family, native to Wet meadows, swamps and stream banks of eastern and central North America. It grows 60 cm–1 m (24 in–3.3 ft) tall and 30–45 cm (12–18 in) wide, wants part sun to part shade and high water, and is hardy to about -35 °C (-31 °F). Space plants about 30 cm (12 in) apart.
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Great blue lobelia at a glance
| Type | Perennial flowering plant, deciduous |
|---|---|
| Family | Campanulaceae |
| Mature height | 60 cm–1 m (24 in–3.3 ft) |
| Mature spread | 30–45 cm (12–18 in) |
| Spacing | 30 cm (12 in) centre to centre |
| Sun | Part sun to part shade, at least 4 h of direct sun a day |
| Water | High; drought tolerance none, waterlogging tolerance high |
| Soil pH | 5.5–7.5 |
| Cold hardiness | About -35 °C (-31 °F) once established (roughly USDA zone 3) |
| Heat stress | Likely above about 32 °C (90 °F) |
| Flowering | from about August for 5–7 weeks (northern hemisphere; later in cold climates, earlier in warm ones) |
| Wind tolerance | Low |
| Pollinator value | High |
| Edible | Not grown as food |
| Native to | Wet meadows, swamps and stream banks of eastern and central North America |
| Common in gardens of | 🇺🇸 United States, 🇨🇦 Canada, 🇬🇧 United Kingdom, 🇩🇪 Germany |
Is Great blue lobelia toxic?
- People: moderately toxic
- Cats: moderately toxic
- Dogs: moderately toxic
- Parts: all parts
Contains lobeline and other alkaloids: eating it causes nausea, vomiting and, in quantity, dangerous effects on breathing and heart.
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 Great blue lobelia
No well-documented helpful pairing. Group it with plants that like part sun to part shade and high water.
Questions about Great blue lobelia
- How far apart should I plant Great blue lobelia?
- About 30 cm (12 in) apart, centre to centre. A mature plant spreads 30–45 cm (12–18 in).
- Does Great blue lobelia need full sun?
- Part sun to part shade: at least 4 hours of direct sun a day.
- How much water does Great blue lobelia need?
- High water. Drought tolerance is none and waterlogging tolerance high.
- How cold-hardy is Great blue lobelia?
- It tolerates about -35 °C (-31 °F) once established, roughly USDA zone 3.
- When does Great blue lobelia flower?
- From about August for 5–7 weeks (northern hemisphere; later in cold climates, earlier in warm ones).
- Is Great blue lobelia poisonous to cats and dogs?
- For cats it is moderately toxic; for dogs moderately toxic; for people moderately toxic. Contains lobeline and other alkaloids: eating it causes nausea, vomiting and, in quantity, dangerous effects on breathing and heart.
- What grows well with Great blue lobelia?
- There is no well-documented companion pairing for Great blue lobelia. 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
- Missouri Botanical Garden Plant Finder, Missouri Botanical Garden
- Illinois Wildflowers (descriptions and insect-visitor records), John Hilty, illinoiswildflowers.info
Notes and assumptions
- Spikes of bright blue, two-lipped flowers in late summer, mostly pollinated by bumblebees (its red cousin the cardinal flower is for hummingbirds). Short-lived but self-seeds in damp soil. The species name records an old, mistaken belief that it cured syphilis.
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
- Canterbury bells Campanula medium
- Edging lobelia Lobelia erinus
- Balloon flower Platycodon grandiflorus
- Fairy's thimble Campanula cochleariifolia
- Deodeok (bonnet bellflower) Codonopsis lanceolata
- Cardinal flower Lobelia cardinalis
- Dwarf grassy bells (edraianthus) Edraianthus pumilio
- Dalmatian bellflower (wall bellflower) Campanula portenschlagiana