Lobelia siphilitica
blue cardinal flower
An upright, clump-forming, deciduous herbaceous perennial with green, finely toothed, lance-shaped leaves. Long-lasting spikes of blue flowers appear on sturdy, upright stems from late summer through until mid autumn
Synonyms
Lobelia siphilitica 'Blue Selection'Lobelia siphilitica 'Blau Auslese'
see moreLobelia siphilitica 'Blaue Auslese'
Lobelia siphilitica blue-flowered
Size
Ultimate height
0.5–1 metresTime to ultimate height
2–5 yearsUltimate spread
0.1–0.5 metresGrowing conditions
Moisture
Moist but well–drainedpH
Acid, Alkaline, NeutralColour & scent
| Stem | Flower | Foliage | Fruit | |
| Spring | Green | |||
|---|---|---|---|---|
| Summer | Blue | Green | ||
| Autumn | Blue | Green | ||
| Winter |
Position
- Full sun
- Partial shade
Aspect
South–facing or East–facing or West–facing
Exposure
Exposed or Sheltered Hardiness
H5Botanical details
- Family
- Campanulaceae
- Native to GB / Ireland
- No
- Foliage
- Deciduous
- Habit
- Clump forming, Columnar upright
- Potentially harmful
- Harmful if eaten, skin irritant. Wear gloves and other protective equipment when handling Wear gloves and other protective equipment when handling. Pets: Harmful if eaten, skin irritant. For further information and contact numbers regarding pets, see the HTA guide to potentially harmful plants
- Genus
Lobelia can be annuals, perennials or shrubs, with simple leaves and showy 2-lipped flowers that may be solitary or in racemes or panicles
- Name status
Correct
- Plant range
- Eastern N America
How to grow
Cultivation
Plant in deep, fertile, reliably moist soil in sun or partial shade. Feed every 2 weeks with a balanced liquid fertilizer until midsummer and a low nitrogen fertilizer for the remainder of the growing season. Protect the crown of the plant during winter with a thick, dry mulch
Propagation
Propagate by division of large clumps of plants every second year in the spring
Suggested planting locations and garden types
- City and courtyard gardens
- Cottage and informal garden
- Flower borders and beds
Pruning
Cut down faded flower spikes in autumn
Pests
May be susceptible to slugs
Diseases
May be susceptible to crown rot and a virus
Get involved
The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.