Ornamental · Campanulaceae
Cardinal Flower
Lobelia cardinalis
Give it wet feet and a little shade, and cardinal flower lifts narrow scarlet spikes the hummingbirds chase from bloom to bloom.
Partial shade
Every 2–4 days
USDA 3–9
2–4 ft · 0.6–1.2 m
Overview
Cardinal flower is a native perennial of stream banks, wet meadows, and pond edges across much of North America. Each stem rises into a tall, slender spike crowded with brilliant scarlet flowers, every bloom a narrow tube split into pointed lips, opening from late summer into fall on plants of 2 to 4 feet (60 to 120 cm). The deep, pure red runs the full length of the spike, and the tubular shape fits a hummingbird's bill, which is why hummingbirds do most of the pollinating while butterflies work the flowers too.
Below the flowers, the upright stems carry lance-shaped leaves with finely toothed edges, green and held close along the stalk. The plant is built for medium-to-wet ground rather than the dry beds most perennials want, and the same stems that shrug off a brief flood stand straight and firm above saturated soil. That suits it to a rain garden, a boggy low spot, or the muddy margin of a pond where little else carries this kind of red.
At the base sits a flat rosette of leaves close to the soil, and this is the part that endures. The tall flowering stem is short-lived and fades after a few seasons, but the basal rosettes and the dust-fine seed it drops carry the deep red forward. Leave it to renew and the scarlet spikes keep returning from new crowns year after year.
Care
The short version: part shade to full sun, soil kept consistently moist to wet and never allowed to dry, rich humusy ground, and a yearly nudge from dividing rosettes or letting it self-seed.
Light
Cardinal flower does best in part shade, though it takes full sun where the soil stays wet enough to keep pace. Deep shade leaves the spikes shorter and the red thinner, so it wants bright light and steady moisture together for the fullest, deepest bloom.
Water
This is the one that matters most. Keep the soil consistently moist to wet and never let the root zone dry out, watering every 2 to 4 days in the absence of rain. The fleshy stems even handle brief flooding, which is why the plant belongs at a pond or stream edge.
Soil
Plant it in rich, humusy ground that holds water and runs high in organic matter. A pH from 6.0 to 7.0 suits it well, and the wetter and more fertile the spot, the taller and more crowded the scarlet spikes grow.
Temperature
The crown and stems take brutal cold in stride, holding through winters down to -40°F (-40°C) and pushing on through summer heat up to about 95°F (35°C). That toughness spans USDA zones 3 through 9, so in most gardens the plant returns as a lasting perennial.
Humidity
The plant asks nothing of the air around its leaves, so no humidity reading matters. What counts is wet soil packed around the roots, not any dampness on the foliage.
Feeding
A dark, humus-rich soil supplies most of what the roots draw on. Beyond that, a thin scattering of compost or a balanced fertilizer across the growing season covers everything the plant needs.
Pruning
Cutting away the spent brown spikes stretches the bloom and reins in heavy self-seeding, while the flat basal rosettes are left in place over winter. In cold climates, mulch the roots so frost cannot heave the crowns out of the ground.
Size & spacing
The flowering stems stand 2 to 4 feet (60 to 120 cm) tall and the leafy base spreads 12 to 24 inches (30 to 60 cm) wide. Give each clump that much room so the upright spikes have light and air all around them.
When to plant
Cardinal flower runs on a cool start and a late finish. The fine seed is surface-sown indoors in late winter, the young plants go out after the last frost once the soil has warmed, and the slender scarlet spikes open 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 has few real problems, and almost all of them show first in the leaves and trace back to water, either pests in the damp or stress when the ground dries out. Match the look of the foliage below and fix the moisture, and most trouble clears on its own.
The flowering stems fade and disappear after several years
Cardinal flower is a short-lived perennial, so the tall stem leans on basal offsets and dropped seed to carry on rather than living long itself. Crown rot or frost heaving speeds the loss when the soil dries out or the rosettes go unmulched and lift bare from the ground. Let some seed fall or divide the rosettes in spring, and fresh green crowns renew the stand.
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
Curling leaf margins browning on a drooping summer stem
Browning, curling leaf margins on a drooping stem are drought stress, plain and simple, because cardinal flower will not put up with dry ground. Water deeply to firm the leaves back up, lay organic mulch to hold the moisture, and if the spot keeps drying out, move 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
Ragged bite holes punched across the green rosettes
The moist, shaded ground cardinal flower loves is also where slugs and snails thrive, and they chew straight through the soft young leaves and the flat basal rosettes. Pick them off by hand in the evening, clear the damp litter banked against the crowns, and reach for iron-phosphate bait if the chewed holes keep spreading.
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
Treat the whole plant as poisonous, from the scarlet flowers to the green rosette at its base. Every part holds lobeline and related piperidine alkaloids, which are toxic to dogs, cats, horses, livestock, and people if eaten, bringing nausea, vomiting, and in large amounts effects on the heart and breathing. The plant's own emetic action usually cuts a meal short, but keep it away from pets, grazing animals, and children all the same.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Toxic
Should a cat mouth the red flowers or green leaves, expect drooling, a dull and quiet manner, and vomited food, often alongside diarrhea and a tender belly. A bigger bite can unsettle the heartbeat, so cut stems have no place within a curious cat's reach.
Dogs Toxic
A dog that swallows the leaves or the scarlet blooms tends to drool heavily, turn sluggish, vomit, and pass loose stools. The lobeline that troubles the gut can also unsettle the heart's rhythm once a large mouthful goes down.
Horses Toxic
A horse grazing the foliage draws the same piperidine alkaloids into its body and shows colic, ropey drool, and a weak, heavy-footed droop. A large feeding bears down on its heart and lungs, so the plant belongs far from any paddock rail.
Rabbits Toxic
The lobeline runs through every part, from the red flowers to the green leaves, so this is not safe forage for a rabbit. Nibbling brings on drooling, gut upset, and a listless, off-color animal.
Livestock Toxic
A cow, sheep, or goat that grazes it can sicken, drooling, bringing up its food, and standing dull and heavy at first. A heavy dose reaches into nerve and heart trouble, though its built-in emetic reflex usually halts the meal before much goes down.
Birds Caution
The red blooms and green leaves are no safer for a pet bird, so keep it away from both. Whatever poisons the larger animals leaves a small bird no better off.
People Caution
Not one part of this plant is edible, and a mouthful sets off nausea, vomiting, and a throat that burns raw. Swallowing a true dose can carry into the heart and lungs, so keep it from small children and rinse the sap off your hands.
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 trade plain green leaves for darker, richer foliage. These are the ones worth knowing by their color.
Queen Victoria
Queen Victoria carries deep bronze-purple to maroon leaves whose dark color throws the scarlet flower spikes forward in a striking two-tone show.
Black Truffle
Black Truffle holds foliage so dark it reads almost black-purple under the bright red blooms, the deepest leaf color and the strongest contrast of the group.
Fried Green Tomatoes
Fried Green Tomatoes keeps plain green leaves beneath vivid red flowers and grows with noticeably better garden vigor.
How to propagate
Cardinal flower keeps itself going two ways, and both are simple: split the leafy rosettes it makes at the base, or let the dust-fine seed do the work for you.
DivisionEasy
Spring, by separating the basal rosettes (offsets) from the parent plant. · One growing season
In spring, lift the plant and pull the leafy basal rosettes away from the parent crown, each a small flat cluster of green leaves. Replant every division right away into moist, rich soil and keep it well watered, and it settles 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
Scatter the dust-fine seed on 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. In a damp spot the plant self-seeds freely on its own, which is how a short-lived perennial keeps a stand going.
Myths
Cardinal flower is named because it attracts cardinals.
The name comes from the brilliant cardinal-red of the blooms, the very same red as the robes worn by Roman Catholic cardinals. The flowers actually draw hummingbirds and butterflies, not the bird the plant is named for.
Lobelia looks like a soft, edible herb, safe to taste.
It carries lobeline and related alkaloids that turn toxic once much of it is swallowed, bringing nausea and vomiting and, in larger amounts, more serious effects in both people and animals. No part of this plant is safe to eat.