About
Great blue lobelia (Lobelia siphilitica) is a moisture-loving perennial of streambanks, seeps, and rain garden bottoms in eastern and central North America, producing upright spikes of intense blue tubular flowers in late summer. Height is commonly 2–3 feet (0.6–1 m) with lance-shaped leaves. It pairs with cardinal flower for red-blue drama and belongs anywhere sun hits wet soil without apology. ☀️💧 Sun and Water Requirements: Full sun to light shade; afternoon shade reduces stress where heat and humidity stack. Consistently moist, organic soils are ideal; tolerates brief inundation in swales. Do not maroon it on a dry berm and expect loyalty. ✂️ Propagation: Sow seed on moist surface; tiny seedlings need gentle handling. Divide clumps in early spring before rapid growth. Self-sows where happy—edit volunteers early if design is strict. 🌾 Harvest / Best Use Timing: Leave flowers for hummingbirds and bees; cut a few stems for short-lived bouquets if guilt permits. Seed capsules scatter fine seed—collect intentionally for sharing. Cut back frost-killed stems in late winter to tidy without harming crowns.
Permaculture Functions
- Pollinator: Tubular blue flowers serve bees and hummingbirds during late-season nectar gaps.
- Wildlife Attractor: Stems and seeds support small wildlife interactions in wetland edges.
- Ornamental: Saturated color in moist beds without resorting to thirsty annual imports.
- Water Retention: Thrives in designed swales that slow and polish runoff on site.
Practitioner Notes
- Pairs visually with red Lobelia cardinalis—hummingbirds approve the color scheme.
- Moisture is the entire personality; sand gardens need a different cast.
- Self-seeding can drift upstream in water features—edit before it becomes a coup.
- Short-lived in dry shade—listen to the plant’s passive-aggressive wilting.
Companion Planting
- Dense Blazingstar — drier upper swale forb placed upslope where moisture is less constant
- Switchgrass — matrix grass stabilizing banks while lobelia holds the wet toe
- Bee Balm — mint-family neighbor sharing pollinators if mildew-resistant selections are chosen
- Toxic if eaten in quantity — contains lobeline-related chemistry; not a salad ingredient
- Drought — foliage collapses quickly without soil moisture; wrong plant for xeric virtue signaling