Great Blue Lobelia
Lobelia siphilitica
Family Campanulaceae
True blue is the rarest color in the flower garden, and great blue lobelia delivers it exactly when it matters — spikes of saturated blue in late summer and fall, two to three feet tall, as the last bumblebees and hummingbirds make their rounds.
A moist-soil native for rain gardens and pond edges, it self-sows enough to stay without becoming a project, and deer leave it be — it isn't a plant for eating. Pair it with its scarlet sibling, cardinal flower, and the wet spot becomes the best bed you have.
Full Sun to Part Shade
Moderate water
Moderate growth
Deer-resistant
Native to North America
Attracts hummingbirds
Attracts bees
From the print shop
Growing great blue lobelia? Hang it.
Our Plant Library collection carries great blue lobelia — Lobelia siphilitica, print Nº 217, “Great Blue Lobelia.”
526 designsfrom $12.99white or black backgroundmatte poster, unframed
Will it thrive where you are?
Enter your ZIP — we look up your USDA hardiness zone (2023 map) and check it against what great blue lobelia actually needs.
Hardy inZones 4-9Great Blue Lobelia · Common problems
Common great blue lobelia problems
Pests
1 problem on file
- Almost none
Diseases
1 problem on file
- Rot in stagnant winter wet
Great Blue Lobelia · Growing & propagation
Growing great blue lobelia
- Light
- Full Sun to Part Shade
- Water
- Moderate-High
Moist-soil native, rain-garden plant
Soil- Rich, moist · pH 6.0 - 7.5
Fertilizer- Light compost
Pruning- Leave some to self-sow
Short-lived but self-sows readily in moist, open soil; let some seed. Keep crown clear of heavy mulch.
Spacing- 10-12 in
How to plant & propagate great blue lobelia
- Propagate
- Division or seed
Great Blue Lobelia · Calculators & field guides
A little help in the garden.
Great Blue Lobelia · Yearly calendar
The great blue lobelia year, month by month
Jan
No calendar activity is listed for this month.
BloomBloomAugust to November
What each band means
- Bloom — flowers open — pollinators working, frost on blossoms is the danger.
These are the species' typical months — expect them a few weeks earlier in warm zones and later in cold ones. Watch the plant, not just the calendar.
Great Blue Lobelia · Ecology & uses
Ecology & uses
Lobelia siphilitica
Great Blue Lobelia in the garden system
- Herbaceous layer perennial
- Nectary/insectary
Attracts- Hummingbirds, Bees
Habitat- Wetland
- Moisture
- Wetland / wet-tolerant
- Deer
- Resistant
A safer unfenced choice
- Origin
- Native to North America
What great blue lobelia is grown for
⚠ Toxic if eatenToxic if eaten
Use- Rain gardens
- Use
- Late blue
- Use
- Pollinators
Edibility, identification, and traditional-use notes here are general reference — not medical or veterinary advice, and not a claim that any plant treats or prevents anything. Medicinal ratings record how strongly a plant features in herbal tradition, nothing more. Never eat or dose a plant you have not positively identified. More on how to use this library.
Great Blue Lobelia · Varieties & cultivars
Choosing a great blue lobelia variety
Species (true blue); crosses with cardinal flower give purples ('Vedrariensis')
Sources & plant identity
Know what you’re growing.
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Great Blue Lobelia
Lobelia siphilitica
The plant, at a glance.
- Botanical name
- Lobelia siphilitica
- Plant family
- Campanulaceae
- Growth habit
- Perennial
- Origin
- Native to North America
- USDA plant symbol
- LOSI
- Invasive risk
- Low
Hardiness, size and timing vary with your cultivar, soil and climate.
Rooted in research.
University extension research, brought together with hands-on growing experience at Story Thyme Farms.
Questions
Great Blue Lobelia questions, answered straight.
Do deer eat great blue lobelia?
Rarely — great blue lobelia is considered deer-resistant, which makes it one of the safer unfenced choices in deer country. Hungry deer in a hard winter test every rule, but it's a low-risk pick.
Is great blue lobelia safe for kids and pets?
No — treat it as toxic if eaten. Toxic if eaten Site it accordingly if children or pets roam the garden. This is general reference, not medical or veterinary advice — call a vet or poison control if something has actually been eaten.
How do you propagate great blue lobelia?
Division or seed.
Elsewhere
Where great blue lobelia sits in the library.
Sunflower
Zinnia
Peony
Daylily