Great Blue Lobelia
Lobelia siphilitica — Bellflower Family
A native perennial wildflower in the Bellflower Family that blooms in late summer and thrives in moist to wet soils.
Planting Guide
When to plant
Plant in spring or early fall. Plants may not bloom until their second year when grown from seed.
Spacing
Space plants 1.1–1.5 feet apart. Closer spacing fills in faster and suppresses weeds; wider spacing gives each plant room to reach full size.
Root system
Roots reach at least 12 inches deep at maturity. Plant the crown at or just below soil level.
Growing Conditions
Sunlight
Part sun to part shade — 3 to 6 hours of direct sunlight. It adapts to a range of exposures and does well on the east or west side of a structure.
Soil & pH
Prefers a wide pH range from acidic to neutral (pH 5.5–7.0). Most average garden soils fall in this range; a quick soil test confirms your starting point.
Watering
High moisture needs. This species thrives in consistently moist soil and is well suited to rain gardens, low spots, pond margins, or areas with supplemental irrigation. It does not tolerate dry conditions well; consistent moisture is important throughout the growing season.
Seasonal Care
- Cut back dead stems from last year to 2–3 inches above ground as new growth emerges.
- Top-dress with a thin layer of compost to support the season's growth.
- Water deeply during dry spells; mulch around the base to retain moisture.
- Allow flowers to set seed — the seed heads provide winter interest and feed birds.
- Leave stems and seed heads standing through fall and winter to support overwintering insects and birds.
- Divide or transplant in early fall (6 weeks before first frost) for best establishment.
- Leave the plant standing — hollow stems shelter native bees and other beneficial insects overwinter.
- The seed heads attract finches and sparrows through the coldest months.
- No mulching is needed for established plants; a thin layer of leaves is fine around the crown.
Wildlife & Garden Value
Ecological benefits
- Late-season bloomer — one of the last nectar sources before frost. Essential for monarch butterflies migrating south and native bees building winter fat reserves.
Landscaping uses
- Rain garden plant — thrives in the wet-dry cycles of a bioswale or detention area.
- Pond or stream margin planting for bank stabilization and wildlife habitat.
- Four-season garden interest — combines attractive late bloom with persistent seed heads and fall foliage color.
Where to Buy Great Blue Lobelia
Buy from specialist native plant nurseries to get the true species rather than a cultivar with reduced wildlife value.
- American Meadows — native seeds and plants
- Prairie Moon Nursery — specialist native plant nursery
- Burpee — seeds with planting instructions