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The Plant Guide

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Blue cardinal flower

Lobelia siphilitica

lo-BEE-lee-ah sif-il-IT-ih-kah Audio

This clump-forming perennial has upright leafy stems. From late summer to mid-autumn, it bears dense spikes of light to bright blue tubular, two-lipped flowers with a more prominent lower lip.

Noteworthy CharacteristicsLong-lasting bloom. Suitable for edging, near water, or in a mixed or herbaceous border. U.S. native.

CareGrow in deep, moist soil. Fertilize every two weeks in spring and early summer to improve flowering. Plants may be trimmed as they die back in hot summers.

PropagationDivide in summer. Take bud cuttings in midsummer.

ProblemsRust, smut, leaf spots, and slugs.

  • Genus : Lobelia
  • Plant Height : 1 to 3 feet
  • Zones : 4, 5, 6, 7, 8
  • Plant Width : 6 to 12 inches
  • Bloom Time : Fall, Summer
  • Light : Full Sun to Partial Shade
  • Moisture : Medium to Wet
  • Maintenance : Moderate
  • Plant Type : Perennials
  • Plant Seasonal Interest : Summer Interest
View Comments


  1. user-7007113 08/03/2014

    Hummingbirds love this as well as the red variety of Cardinal Flower!

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