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Great blue lobelia is a great perennial for rain gardens, wetlands, and other wet spaces.

Great blue lobelia is a great perennial for rain gardens, wetlands, and other wet spaces. USDA, NRCS. 2012. The PLANTS Database (http://plants.usda.gov, 8 October 2012). National Plant Data Team, Greensboro, NC 27401-4901 USA.

Lobelia siphilitica

Great Blue Lobelia

FIRST IMPRESSIONS:  Lobelia siphilitica is a clump forming perennial wildflower with toothed lance shaped leaves.  In late summer stems are topped by spiky racemes of intense blue-violet florets.  The blooms entice bees, hummingbirds and butterflies.  Plants prosper in filtered shade with moist soils or in wetter sunny sites.

HABITAT & HARDINESS:  Lobelia siphilitica occurs in Manitoba and Ontario and south from Maine to Georgia and North Dakota to Texas.

Plants are indigenous to wet prairies, moist Blackland prairies, openings in bottomland forests, soggy meadows, gravely seeps, edges of ponds, creeks or ditches and borders of marshes, sloughs, swamps or wet pastures.  This species occurs in both disturbed and high quality habitats.

Plants are hardy from USDA Zones 4-8.

PLANT DESCRIPTION:   Lobelia siphilitica is a tap rooted clumping perennial that forms robust winter rosettes.  In spring unbranched stems rise from a crown that occurs at ground level.

The stems are clothed in oblong to oval toothed leaves. Blades are up to 5” long and 2” wide.  They are medium to dark green with scattered hairs.  The leaves become smaller as the stalk rises.

In late summer foliage is topped by spires of clear blue florets with tiny bracts interspersed.   The florets are tubular with a two lobed upper lip and a prominent three lobed lower lip.

The floral display lasts for 4-6 weeks ending in early autumn.  After flowering, small rounded capsules full of tiny seed form on the stalk.

Plants are 1-4’ tall with a 1-2’ spread.

CULTURAL & MAINTENANCE NEEDSLobelia siphilitica prospers in shaded to partly sunny exposures with moist humus rich soil.  Plants tolerate sunny sites if sufficient moisture is present.

The species adapts to sandy loam and gravelly or clay soil and acid to neutral pH.  Moisture is appreciated but this species is reported to be more drought tolerant than Lobelia cardinalis.

After seed are produced, the flowering stem and roots die.  New offsets soon form and generate roots.  The small offsets are vulnerable in fall and winter so care should be taken not to bury them under thick mulch.

This species is considered to be a short lived perennial but in an appropriate setting it will self-sow and replenish the population.

Foliage is unpalatable to deer and other herbivores but is chewed by snails and slugs.

LANDSCAPE USES:  This species is often used as an Accent, Grouping or Mass planting in for a Rain Garden, Wildlife Garden or Perennial Border.  Lobelia siphilitica has Showy Blooms and is appropriate for Cottage Gardens, Low Maintenance Plantings, moist Meadows, margins of Water Gardens, and soggy Roadsides.

COMPANION & UNDERSTUDY PLANTS:  Try pairing Lobelia siphilitica with Asclepias incarnata 'Ice Ballet', Anemone canadensis, Carex comosa, Chelone glabra, Eupatorium coelestinum or Osmunda cinnamomea.

Lobelia cardinalis could be substituted due to comparable cultural needs and similar red flowers.

TRIVIA:  This species is a member of the Bellflower Family.

Flowers attract native bees, hummingbirds and butterflies.  Deer and other mammalian herbivores generally avoid eating the plant because foliage contains toxic alkaloids.

Lobelia siphilitica is commonly called Great Blue Lobelia as it has larger flowers than most other blue flowered Lobelia spp.


Height:

1-4 ft

Spread:

12-18 in

Spacing:

18-24 in

USDA Hardiness Zone:

4-8

Bloom Color:

Blue, Violet

Lobelia siphilitica Characteristics

Exposure

  • Partial Shade to Full Shade

Critter Resistance

  • Deer Resistant

Attracts Wildlife

  • Hummingbirds
  • Butterflies

Soil Moisture Preference

  • Wet to Moist

Attributes

  • Naturalizing
  • Rain Garden
  • Cut Flower
  • Bog
  • Reblooming

Flowering Months

  • September
  • August
  • July

Foliage Color

  • Green

Season of Interest (Foliage)

  • Summer
  • Spring

Growth Rate

  • Medium

Juglans nigra Tolerance (Black Walnut)

  • Yes

Interesting Notes:

Lobelia siphilitica is a clump forming perennial wildflower with toothed lance shaped leaves.  In late summer stems are topped by spiky racemes of intense blue-violet florets.  The blooms entice bees, hummingbirds and butterflies.  Plants prosper in filtered shade with moist soils or in wetter sunny sites.


Plants that work well with Lobelia siphilitica ''

Palm sedge Palm sedge (Carex muskingumensis)
Palm sedge Palm sedge (Carex muskingumensis 'Oehme')
Turtlehead Turtlehead (Chelone glabra)
Pink turtlehead Pink turtlehead (Chelone lyonii 'Hot Lips')
Mistflower Mistflower (Eupatorium coelestinum)
Three-nerved Joe pye Three-nerved Joe pye (Eupatorium dubium)
Joe pye weed Joe pye weed (Eupatorium fistulosum)
Spotted Joe pye weed Spotted Joe pye weed (Eupatorium maculatum)
Gateway Joe Pye Gateway Joe Pye (Eupatorium maculatum 'Gateway')
Sweet Joe pye weed Sweet Joe pye weed (Eupatorium purpureum)
Path rush Path rush (Juncus tenuis)
Wild sweet William Wild sweet William (Phlox maculata)
Cattail sedge Cattail sedge (Carex typhina)
Riddell's goldenrod Riddell's goldenrod (Solidago riddellii)

Substitutions for Lobelia siphilitica

Cardinal flower Cardinal flower (Lobelia cardinalis)
Cardinal flower Cardinal flower (Lobelia cardinalis 'New Moon Maroon')
Meadow beauty Meadow beauty (Rhexia virginica)