Lobelia siphilitica

Lobelia siphilitica: Cool Blue Spires for Sun and Shade

Elegant and unassuming, Lobelia siphilitica brings soft structure and cool-toned beauty to late-summer gardens. Native to eastern North America, this clump-forming perennial produces upright spikes of clear blue flowers that invite pollinators and add vertical grace to moist, sunny, or partly shaded settings.

Plant Characteristics:

• Height: 60–90 cm
• Spread: 30–45 cm, upright and clump-forming
• Flower Colour: Soft to medium blue
• Flowering Period: Late summer to early fall
• Foliage: Medium green, lance-shaped leaves
• Sunlight Requirements: Full sun to part shade
• Soil Requirements: Moist, rich soil; tolerates average soil with regular moisture

Uses and Benefits: Lobelia siphilitica is a reliable performer in rain gardens, native plantings, and along streams or pond edges. Its clear blue blooms provide a rare and welcome colour in late summer, especially among the warm tones of autumn. A favourite of bumblebees and long-tongued pollinators, it’s an easy and adaptable perennial that bridges sun and shade with grace.

Companion Plants: Pair Lobelia siphilitica with Echinacea purpurea for a classic native combination of complementary colour and pollinator support. Add Amsonia hubrichtii, whose fine foliage and golden autumn tones offer elegant contrast to the lobelia’s blue blooms. Include Schizachyrium scoparium for late-season texture and movement—its soft vertical lines echo the lobelia’s form while adding warm, native prairie structure.

Care Instructions: Grow in full sun to part shade in moist, well-drained soil. Tolerates average garden conditions with consistent watering. Cut back stems after flowering if reseeding is not desired. Divide every 3–4 years in early spring to refresh clumps and maintain vigour.

History: Lobelia siphilitica, or great blue lobelia, is native to eastern and central North America. Historically used by Indigenous peoples, it is valued today for its wildlife benefits, adaptability, and uncommon blue flower colour during the late-summer lull.

Final Thoughts: With cool blue blooms and native charm, Lobelia siphilitica brings calm beauty and ecological richness to gardens that celebrate both structure and sustainability.