How to Grow Great Blue Lobelia
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Great Blue Lobelia
Lobelia siphilitica
flowerGreat blue lobelia is a native North American perennial wildflower prized for its vibrant blue-purple flower spikes that attract hummingbirds and pollinators. This tall, elegant plant thrives in moist habitats and blooms from late summer through fall, adding vertical interest and color to shaded garden spaces. It's an excellent choice for naturalized areas, rain gardens, and woodland borders.
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Example Great Blue Lobelia timeline · Pittsburgh, PA (Zone 6b)
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Plant Great Blue Lobelia
Around Apr 17Near Pittsburgh's average last spring frost.
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Tend & protect
Late spring–summerWatering, feeding, and pest-watch reminders.
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First Great Blue Lobelia blooms
Mid-to-late summerBefore the first fall frost (≈ Nov 8)
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Growing Conditions
Soil
Growing Zones
Find your zone →Thrives best in zones 3-8, tolerates zone 9 with afternoon shade and consistent moisture
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Get my Great Blue Lobelia timeline →Growth Stages
Germination & Seedling
2-4 weeksTiny seeds germinate on soil surface under light and moist conditions. First true leaves emerge within 2-3 weeks. Seedlings are delicate with minimal foliage.
Keep soil consistently moist but not waterlogged. Provide bright, indirect light. Do not cover seeds. Thin seedlings to prevent crowding. May benefit from stratification over winter for better germination.
Vegetative Growth (Year 1)
5-7 monthsPlant develops rosette of narrow, lance-shaped leaves close to the ground. Slow to moderate growth with minimal height gain in first season.
Maintain consistent moisture. Mulch lightly to retain moisture and regulate temperature. Keep weeds suppressed. No flowering expected in year one.
Spring Growth (Year 2)
4-6 weeksFoliage expands rapidly as temperatures warm. Tall, slender stems with narrow leaves emerge, reaching 2-4 feet tall depending on variety and conditions.
Increase watering as plant grows. Provide stakes or support for tall stems in windy locations. Ensure adequate moisture for vigorous growth. Fertilize lightly with balanced fertilizer if soil is poor.
Flowering
6-8 weeksTall spikes of brilliant blue-purple flowers emerge from mid-summer to early fall. Individual flowers open progressively from bottom to top. Plants reach full height of 2-4 feet with dense flower clusters.
Maintain consistent moisture throughout flowering period. Deadhead spent lower flowers to encourage continued blooming and tidy appearance. Stake tall varieties if needed. Plants attract hummingbirds and butterflies.
Seed Development & Maturation
4-6 weeksFlowers fade to brown seed capsules. Foliage may yellow and decline. Stems gradually dry and harden. Plant energy transfers to seed production.
Allow seeds to fully mature on plant if self-seeding is desired. Collect seed capsules before they fully dry and split open. Leave some mature seed heads for wildlife and natural reseeding. Cut back dead foliage in late fall or early spring.
Companion Planting
Plan your garden →Plant with:
Avoid planting near:
Common Pests
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and
Remove by hand, use copper tape barriers, encourage ground beetles, apply organic slug bait if severe
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Increase humidity by watering foliage in morning, use strong water spray to dislodge, apply neem oil if infestation is severe
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Spray with strong water stream, encourage ladybugs and parasitic wasps, use insecticidal soap if necessary
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Improve air circulation, avoid overhead watering, apply sulfur dust or baking soda spray at first sign
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Ensure excellent drainage, avoid waterlogging, remove affected plants, do not plant in poorly drained sites
Uses
Hummingbird & Pollinator Magnet
WildlifeGreat blue lobelia is a premier native plant for attracting Ruby-throated hummingbirds, bumblebees, and other pollinators. The tall flower spikes with tubular blooms are perfectly shaped for hummingbird bills and provide abundant nectar throughout late summer and fall. [source]
Historical Medicinal Use
CulinaryHistorically used by Native Americans and early settlers as a remedy for respiratory issues and fever. The plant was listed in early American pharmaceutical texts, though modern medical use is limited. All parts contain alkaloids and should not be ingested without expert guidance. [source]
Fresh & Dried Cut Flowers
HouseholdThe striking blue-purple flower spikes make excellent fresh arrangements for late summer and fall bouquets. Dried seed heads also provide architectural interest and can be used in dried arrangements and floral crafts. [source]
Seed Collection & Gardening
CraftGreat blue lobelia produces copious amounts of tiny seeds ideal for gardeners interested in seed saving and propagation. Seeds can be collected, stored, and shared with other gardeners, making it excellent for habitat restoration projects. [source]
Rain Garden & Wetland Plant
WildlifeAn ideal choice for bioswales, rain gardens, and naturalized wetland areas where it provides erosion control and water filtration while beautifying the landscape. Its tolerance for wet feet makes it valuable in difficult moist site plantings. [source]
Harvest Tips
For cut flowers: Cut stems in early morning when dew is still present, choosing stems with multiple flowers beginning to open. Place in water immediately. Flowers last 7-10 days in a vase. For seeds: Allow seed pods to mature on plant until brown and papery (late fall). Cut entire seed head and place in paper bag. Dry in warm location for 1-2 weeks, then shake to release seeds. Store dry seeds in cool, dark location for up to 2 years.
Fun Facts
- 🌱 Great blue lobelia is native to moist woodlands, stream banks, and wetlands throughout eastern North America, from Canada to the Carolinas, making it perfectly adapted to humid growing conditions.
- 🌱 The common name 'siphilitica' comes from early historical use—the plant was once believed to treat syphilis, though this claim was never scientifically validated.
- 🌱 Lobelia flowers feature an unusual specialized pollination mechanism: the stamen tube forms around the pistil, and hummingbirds must push through this structure to access nectar, which brushes pollen onto their faces for transfer to other flowers.
Gardening Terms
New to gardening? Learn about terms used in this guide:
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