Lobelia siphilitica

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blue cardinal flower

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Other common names

great lobelia, tall blue lobelia, Virginia bellflower, vomit root

Synonyms

Lobelia siphilitica 'Blue Selection'
Lobelia siphilitica 'Blau Auslese'
Lobelia siphilitica 'Blaue Auslese'
Lobelia siphilitica blue-flowered

Herbaceous Perennial
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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

Position

Full sun, Partial shade

Soil Types

Chalk, Clay, Loam, Sand

Max Height

0.5-1 metres

Max Spread

0.1-0.5 metres

Size

Time to Maturity
2–5 years
Max Spread
0.1-0.5 metres
Max Height
0.5-1 metres

Growing Conditions

Chalk Clay Loam Sand
Moisture
Moist but well–drained
pH
Acid or Alkaline or Neutral

Position

Full sun Partial shade
Aspect
South–facing or East–facing or West–facing
Exposure
Exposed or Sheltered
Hardiness

Hardiness Ratings

All ratings refer to the UK growing conditions unless otherwise stated. Minimum temperature ranges (in degrees C) are shown in brackets

  • H1A: under glass all year (>15C)
  • H1B: can be grown outside in the summer (10 - 15)
  • H1C: can be grown outside in the summer (5 - 10)
  • H2: tolerant of low temperatures, but not surviving being frozen (1 to 5)
  • H3: hardy in coastal and relatively mild parts of the UK (-5 to 1)
  • H4: hardy through most of the UK (-10 to -5)
  • H5: hardy in most places throughout the UK even in severe winters (-15 to -10)
  • H6: hardy in all of UK and northern Europe (-20 to -15)
  • H7: hardy in the severest European continental climates (< -20)
H5

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Campanulaceae
Native to GB/Ireland
No
Foliage
Deciduous
Habit
Clump forming, Columnar upright
Potentially harmful
Harmful if eatenskin irritant. Wear gloves and other protective equipment when handling Wear gloves and other protective equipment when handling. Pets: Harmful if eatenskin 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