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Herbaceous Perennial

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

Other common names
great lobelia
tall blue lobelia
see moreVirginia bellflower
vomit root
Synonyms
Lobelia siphilitica 'Blue Selection'
Lobelia siphilitica 'Blau Auslese'
see moreLobelia siphilitica 'Blaue Auslese'
Lobelia siphilitica blue-flowered
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Size
Ultimate height
0.5–1 metres
Time to ultimate height
2–5 years
Ultimate spread
0.1–0.5 metres
Growing conditions
Chalk
Clay
Loam
Sand
Moisture
Moist but well–drained
pH
Acid, Alkaline, Neutral
Colour & scent
StemFlowerFoliageFruit
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
H5
Botanical 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

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