Ornamental · Campanulaceae
Cardinal Flower
Lobelia cardinalis
Plant it somewhere with wet feet and a bit of shade, and cardinal flower will reward you with scarlet spikes the hummingbirds adore.
Partial shade
Every 2–4 days
USDA 3–9
2–4 ft · 0.6–1.2 m
Overview
If you have a damp corner that nothing else seems to like, cardinal flower may become your new favorite. This native perennial grows wild along stream banks, wet meadows, and pond edges across much of North America, so it already knows how to look after itself. From late summer into fall it raises tall spikes of brilliant scarlet flowers on plants that reach 2 to 4 feet (60 to 120 cm), and hummingbirds do most of the pollinating while butterflies join in too.
The thing that trips up so many perennials, a soggy spot, is exactly what this one wants. Where other plants need sharp drainage, cardinal flower asks for medium-to-wet ground that never quite dries, and it forgives the occasional flood without complaint. That makes the muddy edge of a pond, a boggy low patch, or a rain garden the easiest place in the world to keep it happy.
Do not worry if your first clump seems to fade. The parent plant is short-lived by nature, often slipping away after a few seasons, yet it quietly leaves behind basal rosettes and scatters seed to take its place. Give it the freedom to renew itself and one small planting will keep your wet corner in flower for years to come.
Care
The short version: give it part shade to full sun, keep the soil steadily moist to wet so it never dries out, plant it in rich humusy ground, and once a year either divide a few rosettes or simply let it self-seed.
Light
Cardinal flower is happiest in part shade, and it will gladly take full sun as long as the soil stays wet enough to keep up. Too much deep shade will thin the flowering, so aim for a spot with some bright light and reliable moisture together and it will do the rest.
Water
This is the one part to stay on top of, and it is not hard once you get into the habit. Keep the soil consistently moist to wet and never let the roots dry out, watering every 2 to 4 days when rain is scarce. It even shrugs off brief flooding, which is why a pond or stream edge suits it so well.
Soil
Settle it into rich, humusy ground that holds onto water and is full of organic matter. A pH between 6.0 and 7.0 keeps it comfortable, and the wetter and more fertile the spot, the more relaxed and healthy the plant will be.
Temperature
You can relax about cold, because this plant is tough. It takes winters down to -40°F (-40°C) and summers up to about 95°F (35°C), which covers USDA zones 3 through 9. That means most gardeners can leave it in the ground as a permanent perennial without any fuss.
Humidity
There is nothing to measure or worry about here, since ordinary outdoor air is plenty. What truly matters to this plant is wet soil around the roots, not any particular dampness in the air.
Feeding
Rich organic soil usually does the feeding for you, so you can keep things light. A gentle topdressing of compost or a balanced fertilizer through the growing season is all the extra nourishment it really asks for.
Pruning
Snipping off the spent spikes will stretch the flowering and gently curb heavy self-seeding, while the basal rosettes are best left alone over winter. In cold climates, tuck a little mulch over the roots so frost cannot heave the crowns up out of the ground.
Size & spacing
Expect plants to stand 2 to 4 feet (60 to 120 cm) tall and spread 12 to 24 inches (30 to 60 cm) across. Giving each clump that much room lets light and air move freely around the spikes, which keeps the whole planting looking its best.
When to plant
Cardinal flower likes a cool start and a long, late finish, and the rhythm is easy to follow. Surface-sow seed indoors in late winter, move your young plants outside after the last frost once the soil has warmed, and you can look forward to scarlet spikes opening 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
Take heart: cardinal flower has very few troubles, and nearly all of them come back to one friendly thing to remember, which is water. Pests turn up where it stays damp, and stress shows when the ground dries out. Match what you see below, sort out the moisture, and most problems quietly fix themselves.
The clump quietly fades away after a few years
This is nothing you did wrong, because cardinal flower is a short-lived perennial that leans on basal offsets and dropped seed to carry on rather than living long itself. Crown rot or frost heaving can hurry it along when the soil dries or the rosettes go unmulched. Let a little seed fall or divide the rosettes in spring, and your stand will happily renew itself.
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
Wilting, browning leaf edges, and stalled growth in summer
What you are seeing is drought stress, simply because this plant will not put up with dry ground. The fix is gentle and quick: water deeply to bring the moisture back, lay down organic mulch to hold it there, and if the spot keeps drying out, move the plant to a wetter home such as 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
Tender leaves and rosettes left full of ragged holes
The cool, damp, shady ground that cardinal flower loves is sadly the same place slugs and snails feel at home, and they head straight for the soft young growth. Do not be discouraged: step out in the evening to pick them off by hand, sweep away the damp litter pressed against the crowns, and lean on iron-phosphate bait if they keep returning.
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
Please treat the whole plant as poisonous, and you will both be fine. 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 stops a meal early, but it is still kindest to keep it away from pets, grazing animals, and children.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Toxic
A cat that nibbles any part may start drooling, turn quiet and dull, and bring its food back up, often alongside diarrhea and a tender belly. Bigger mouthfuls can unsettle the heartbeat, so it is wise not to leave cut stems where a curious cat can get to them.
Dogs Toxic
After a dog eats the leaves or flowers, look for heavy drooling, low energy, vomiting, and loose stools. The same lobeline that upsets the stomach can disturb the heart rhythm when a dog manages a large mouthful, so keep an eye on portions.
Horses Toxic
Horses grazing the foliage take in the same piperidine alkaloids and tend to show colic, drooling, and weakness. A heavy feed can press on the heart and breathing, so it is safest to keep this plant well clear of paddocks.
Rabbits Toxic
Because the lobeline runs through every part, this is simply not safe forage for a rabbit. A nibble can bring on drooling, gut upset, and a listless, off-color animal, so keep it out of reach.
Livestock Toxic
Cattle, sheep, and goats can be poisoned if they graze it, with salivation, vomiting, and dullness showing up first. A large dose moves into nervous and heart trouble, though the plant's own emetic kick usually cuts the meal short before it gets that far.
Birds Caution
It is kindest to treat this as unsafe and keep pet birds away from the leaves and flowers. The alkaloids that sicken other animals give no reason to expect a bird would handle them any better.
People Caution
No part of this plant is food, and eating it brings nausea, vomiting, and a burning throat. Swallowing a real amount can reach the heart and breathing, so keep it away from children and wash your hands after handling 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 you will find are the plain scarlet species, which is lovely on its own, but a few selections swap in darker leaves for extra drama. Here are the ones worth getting to know.
Queen Victoria
Deep bronze-purple to maroon leaves give Queen Victoria a rich backdrop that makes the scarlet flower spikes pop for a lovely two-tone display.
Black Truffle
With foliage so dark it reads almost black-purple beneath bright red blooms, Black Truffle offers the boldest contrast of the bunch.
Fried Green Tomatoes
Fried Green Tomatoes keeps green leaves and pairs them with vivid red flowers, and it tends to grow with noticeably better garden vigor.
How to propagate
Good news for a beginner: cardinal flower happily multiplies in two simple ways. You can split the little rosettes it forms at its base, or you can sit back and let the fine seed do the work for you.
DivisionEasy
Spring, by separating the basal rosettes (offsets) from the parent plant. · One growing season
Come spring, gently lift the plant and ease the basal rosettes away from the parent crown. Pop each division straight back into moist, rich soil, keep it well watered, and you will find it settles in comfortably 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 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 grown this way usually flower the year after sowing. In a damp spot it also self-seeds freely on its own, which is exactly how a short-lived perennial quietly keeps its stand going.
Myths
Cardinal flower earns its name by attracting cardinals.
The name actually points to the rich cardinal-red of the blooms, the very same red as the robes worn by Roman Catholic cardinals. In truth the flowers call in hummingbirds and butterflies, not the bird the plant happens to share a name with.
Lobelia is a mild herb that is safe to eat.
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.