• Eventual height: 1m
  • Eventual spread: 0.3m

Lobelia siphilitica

blue cardinal flower

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This perennial dies back to below ground level each year in autumn, then fresh new growth appears again in spring.

  • Position: full sun
  • Depth of water: 0-5cm (0-2")
  • Rate of growth: average
  • Flowering period: July to September
  • Hardiness: fully hardy


Displaying an upright and clump-forming habit, this deciduous herbaceous perennial boasts finely toothed, lance-shaped leaves in a refreshing shade of light green. As summer transitions to autumn, Lobelia siphilitica takes centre stage with its enduring spikes of true blue tubular flowers. These vibrant blooms grace sturdy, upright stems, creating an enchanting visual display in reliably moist or boggy garden settings.


  • Garden care:
    Plant out in reliably moist or boggy soil, or pot up into a pond basket and place at the margins of a pond in shallow water no deeper than 5cm (2"). A low maintenance plant, cut back foliage to ground/water level at the end of the year. Divide congested clumps in early spring every few years. Protect the crown of the plant during winter with a thick, dry mulch.
    • Humans/Pets: Harmful if eaten; skin irritant
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