Ornamental · Campanulaceae
Cardinal Flower
Lobelia cardinalis
Give it wet feet and a little shade, and cardinal flower fires off scarlet spikes that send hummingbirds into a frenzy all late summer.
Partial shade
Every 2–4 days
USDA 3–9
2–4 ft · 0.6–1.2 m
Overview
Cardinal flower turns a soggy corner into the best show in the garden. This North American native of stream banks, wet meadows, and pond edges launches tall spikes of brilliant scarlet flowers from late summer into fall on plants that climb 2 to 4 feet (60 to 120 cm). Hummingbirds zip in to do most of the pollinating, and butterflies pile on too, so the whole patch hums with movement.
Here is the part that hooks growers. Almost every perennial wants sharp drainage, but cardinal flower flips that and chases medium-to-wet ground that never dries, and it powers right through the odd flood. That makes a rain garden, a boggy dip, or the muddy rim of a pond a dream posting, the exact spot where most plants give up and this one takes off.
One quirk keeps things interesting. The starting clump is short-lived and often bows out after a few seasons, but it fires out basal rosettes and scatters seed that leap in to replace it. Let it run with that and a single planting holds its ground year after year, basically renewing itself while you watch.
Care
The short version: part shade to full sun, soil kept moist to wet and never left to dry, rich humusy ground, and a quick yearly move to divide a few rosettes or just let it self-seed.
Light
Cardinal flower hits its stride in part shade, and it grabs full sun too where the soil stays wet enough to keep pace. Deep shade saps the bloom, so pair some bright light with steady moisture and it really takes off.
Water
This is the one to nail. Keep the soil consistently moist to wet and never let the root zone dry out, watering every 2 to 4 days when the rain stalls. It even powers through brief flooding, which is exactly why it belongs at a pond or stream edge.
Soil
Drop it into rich, humusy ground that grips water and runs high in organic matter. A pH from 6.0 to 7.0 hits the mark, and the wetter and more fertile the spot, the harder it goes.
Temperature
It shrugs off serious cold, taking winters down to -40°F (-40°C) and summers up to about 95°F (35°C). That tough streak covers USDA zones 3 through 9, so most gardeners can run it as a permanent perennial.
Humidity
No humidity to chase here, since ordinary outdoor air does the trick. What fuels this plant is wet soil at the roots, not moisture in the air.
Feeding
Rich organic soil already feeds it well, so keep it light. A quick topdressing of compost or a balanced fertilizer through the growing season covers anything extra it wants.
Pruning
Snap off the spent spikes to push the bloom further and keep self-seeding from running wild, but leave the basal rosettes alone over winter. In cold climates, mulch the roots so frost cannot heave the crowns up out of the ground.
Size & spacing
Plants shoot up 2 to 4 feet (60 to 120 cm) tall and spread 12 to 24 inches (30 to 60 cm) wide. Hand each clump that much room and the spikes get all the light and air they crave.
When to plant
Cardinal flower kicks off cool and finishes strong and late. Surface-sow seed indoors in late winter, push plants outside after the last frost once the soil warms, and the scarlet spikes erupt from midsummer through mid-fall.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: Surface sow on moist medium in late winter; seed needs light and benefits from cold stratification.
- Plant: After last frost in spring once soil has warmed.
- Harvest: Late summer through mid-fall (July to October).
Hardiness
USDA hardiness zones: 3–9
Temperature: down to -40°C
Troubleshooting
Cardinal flower throws very few curveballs, and nearly all of them circle back to one thing, which is water. Pests crowd in where it stays damp, and the plant pushes back with stress when the ground dries out. Match what you spot below, dial in the moisture, and most trouble clears fast.
The clump peters out within a few years
No alarm needed, because cardinal flower is a short-lived perennial that rides basal offsets and dropped seed to carry on rather than living long itself. Crown rot or frost heaving speeds the exit when the soil dries out or the rosettes go unmulched. Let some seed fall or divide the rosettes in spring, and the stand bounces right back.
Fix:
- Allow some seed to drop or collect and resow to maintain the stand
- Divide and replant basal rosettes in spring
- Mulch crowns in cold climates to prevent heaving
Wilted leaves and browned edges stalling in summer heat
This is drought stress, flat out, since cardinal flower refuses to deal with dry ground. Water deeply to drive the moisture back, lay down organic mulch to lock it in, and if the spot keeps drying out, shift the plant to a wetter home like a rain garden or pond edge.
Fix:
- Water deeply to restore even moisture
- Add organic mulch to retain soil moisture
- Relocate to a wetter site such as a rain garden or pond edge
Foliage shredded with ragged bite marks
That damp, shaded ground cardinal flower loves doubles as prime turf for slugs and snails, and they charge straight at the tender young growth. Stake out the patch in the evening and pluck them off by hand, sweep away the damp litter banked against the crowns, and bring in iron-phosphate bait if they keep storming back.
Fix:
- Hand-pick slugs and snails in the evening
- Reduce surface debris and mulch piled against crowns
- Use iron-phosphate slug bait if pressure is high
Toxicity
As much fun as it is to grow, treat the whole plant as poisonous. Every part packs lobeline and related piperidine alkaloids, which hit dogs, cats, horses, livestock, and people if eaten, firing off nausea, vomiting, and in big amounts effects on the heart and breathing. Its own emetic action usually cuts a meal short, but keep it well away from pets, grazing animals, and children all the same.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Toxic
A cat that chews any part may drool, go quiet and dull, and bring up its food, often with diarrhea and a sore belly. Larger amounts can throw off the heartbeat, so never leave cut stems where a curious cat can reach them.
Dogs Toxic
After a dog eats the leaves or flowers, watch for heavy drooling, low energy, vomiting, and loose stools. The same lobeline that upsets the gut can disturb the heart rhythm when a dog gets into a big mouthful.
Horses Toxic
Grazing horses absorb those piperidine alkaloids and show drooling, colic, and a weak, unsteady stance. Eating much of it bears down on heart and breathing, so set the plant well away from any paddock.
Rabbits Toxic
Every part carries the lobeline, so a rabbit gets no safe forage here. A few nibbles bring on drooling, an upset gut, and a listless, washed-out animal.
Livestock Toxic
Turn cattle, sheep, or goats loose on it and they can sicken, drooling, vomiting, and dull from the outset. Enough of it drives into nerve and cardiac distress, though its own emetic reflex tends to end the feast fast.
Birds Caution
Chalk it up as unsafe and steer pet birds well clear of the foliage and the flower spikes. The same alkaloids that lay other animals low give a bird no reason to expect an easier time.
People Caution
None of this plant is food, and a bite fires off nausea, vomiting, and a scorched throat. Down a real amount and it can hit the heart and lungs, so keep it out of children's reach and scrub your hands after any contact with the sap.
Keep away from pets and grazing animals; wash hands after handling sap.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
Poison Control: (800) 222-1222
Canada
Poison Centres: 1-844-764-7669
Varieties
Most cardinal flowers sold are the straight scarlet species, but a few selections crank up the foliage for extra drama. These are the ones worth chasing down.
Queen Victoria
Queen Victoria fires deep bronze-purple to maroon leaves under the scarlet flower spikes for a striking two-tone show.
Black Truffle
Black Truffle pushes the foliage to an almost black-purple beneath bright red blooms for the boldest contrast of the group.
Fried Green Tomatoes
Fried Green Tomatoes keeps green leaves, pairs them with vivid red flowers, and charges ahead with noticeably better garden vigor.
How to propagate
Cardinal flower hands you two easy ways to make more, and both deliver: split the rosettes it pumps out at the base, or turn the fine seed loose to do the job for you.
DivisionEasy
Spring, by separating the basal rosettes (offsets) from the parent plant. · One growing season
Come spring, lift the plant and tease the basal rosettes off the parent crown. Drop each division straight into moist, rich soil, keep it well watered, and it digs in over a single growing season.
SeedEasy
Surface-sow on moist medium in late winter to early spring; seed needs light to germinate. · Blooms typically in the year after sowing
Fling the fine seed across the surface of a moist mix in late winter to early spring and leave it uncovered, since it needs light to sprout. Plants raised this way usually flower the year after sowing. Park it in a damp spot and it self-seeds freely on its own, which is how a short-lived perennial keeps a stand going.
Myths
Cardinal flower earns its name by attracting cardinals.
The name fires straight off the brilliant cardinal-red of the blooms, the same red as the robes worn by Roman Catholic cardinals. The flowers actually pull in hummingbirds and butterflies, not the bird the plant is named for.
People treat lobelia as a harmless, edible herb.
It packs lobeline and related alkaloids that turn toxic once much of it goes down, kicking off nausea and vomiting and, in larger amounts, more serious effects in both people and animals. No part of this plant is safe to eat.