Ornamental · Campanulaceae
Cardinal Flower
Lobelia cardinalis
Give it wet feet and a little shade, and you'll get scarlet spikes the hummingbirds can't resist all late summer.
Partial shade
Every 2–4 days
USDA 3–9
2–4 ft · 0.6–1.2 m
Overview
Got a soggy spot you can't figure out what to do with? Cardinal flower is your answer. It's a North American native from stream banks, wet meadows, and pond edges, and it throws up tall spikes of brilliant scarlet flowers from late summer into fall on plants that hit 2 to 4 feet (60 to 120 cm). Hummingbirds handle most of the pollinating, and butterflies stop by too.
Here's the twist. Almost every perennial begs for good drainage, but this one wants the exact opposite. It's happiest in medium-to-wet ground that never really dries, and it doesn't mind the odd flood either, so a rain garden, a boggy dip, or the muddy rim of a pond is right up its alley, basically anywhere most plants would sulk.
One thing to know up front: the first clump won't stick around forever. It's short-lived and tends to fade after a few seasons, but don't sweat it, because it leaves basal rosettes behind and drops seed that fills right back in. Let it do its own thing and a single planting keeps going for years.
Care
The short version: part shade to full sun, soil that stays moist to wet and never dries out, rich humusy ground, and a quick yearly nudge from dividing rosettes or just letting it self-seed.
Light
Cardinal flower likes part shade best, but it'll take full sun no problem as long as the soil stays wet enough to keep up. Stick it in deep shade and you'll get fewer flowers, so give it some bright light and steady moisture together and it's golden.
Water
This is the big one. Keep the soil consistently moist to wet and never let the roots dry out, watering every 2 to 4 days when it isn't raining. It'll even sit through brief flooding without a fuss, which is exactly why it belongs at a pond or stream edge.
Soil
Plant it in rich, humusy ground that hangs onto water and is loaded with organic matter. A pH from 6.0 to 7.0 works great, and the wetter and more fertile the spot, the happier it'll be.
Temperature
Worried about winter? Don't be, because this plant's seriously tough. It handles cold down to -40°F (-40°C) and heat up to about 95°F (35°C), which covers USDA zones 3 through 9, so most folks can just leave it in the ground year after year.
Humidity
There's nothing to fuss over here, since regular outdoor air is plenty. What it actually cares about is wet soil at the roots, not how damp the air is.
Feeding
Rich organic soil usually feeds it just fine on its own. A light topdressing of compost or a balanced fertilizer through the growing season is all the extra it really wants.
Pruning
Snip off the spent spikes to keep the bloom going and rein in heavy self-seeding, but leave the basal rosettes be over winter. Somewhere cold? Mulch the roots so frost can't shove the crowns up out of the soil.
Size & spacing
Plants come in at 2 to 4 feet (60 to 120 cm) tall and spread 12 to 24 inches (30 to 60 cm) wide. Give each clump that kind of room and the spikes get all the light and air they need.
When to plant
It runs on a cool start and a late finish, which is easy enough to work with. Surface-sow seed indoors in late winter, set plants out after the last frost once the soil's warmed up, and you'll see scarlet spikes 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
Good news: cardinal flower barely has any problems, and the few it does have come down to water. Pests like it when things are damp, and the plant sulks when the ground dries out. So find your symptom below, fix the moisture, and most of it sorts itself out.
The clump fades and vanishes after a few years
Nothing's wrong here, because cardinal flower is a short-lived perennial that gets by on basal offsets and dropped seed instead of living long itself. Crown rot or frost heaving just speeds things up when the soil dries out or the rosettes go unmulched. Let a little 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
Wilting, browning leaf edges, and stalled growth in summer
This is drought stress, pure and simple, since cardinal flower just won't deal with dry ground. Water it deeply to bring the moisture back, lay down some organic mulch to keep it there, and if the spot keeps drying out, move the plant somewhere wetter 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 holes chewed through the leaves and rosettes
That damp, shady ground cardinal flower loves? Slugs and snails love it just as much, and they make a beeline for the soft young growth. Head out in the evening and pick them off by hand, clear away the damp litter piled up against the crowns, and if they keep showing up, grab some iron-phosphate bait.
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
Just treat the whole plant as poisonous and you're set. Every part's got lobeline and related piperidine alkaloids, which are toxic to dogs, cats, horses, livestock, and people if they eat it, bringing on nausea, vomiting, and in big amounts trouble for the heart and breathing. It's its own emetic, so it usually cuts a meal short, but keep it away from pets, grazing animals, and kids anyway.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Toxic
A cat that chews any part might drool, get quiet and dull, and throw up its food, often with diarrhea and a sore tummy. Bigger amounts can mess with the heartbeat, so don't leave cut stems lying where a curious cat can get at them.
Dogs Toxic
If a dog eats the leaves or flowers, watch for heavy drooling, low energy, vomiting, and loose stools. That same lobeline upsetting the gut can throw off the heart rhythm when a dog gets into a big mouthful.
Horses Toxic
Horses that graze the foliage take in the same piperidine alkaloids and end up with colic, drooling, and weakness. A big helping can press on the heart and breathing, so keep the plant well away from paddocks.
Rabbits Toxic
The lobeline's in every single part, so this isn't safe forage for a rabbit, no question. A nibble brings on drooling, gut upset, and a listless, off-color animal.
Livestock Toxic
Cattle, sheep, and goats can get poisoned if they graze it, and you'll see salivation, vomiting, and dullness first. A big dose pushes into nervous and heart trouble, though the plant's own emetic kick usually cuts the meal short.
Birds Caution
Just treat it as unsafe and keep pet birds away from the leaves and flowers. The alkaloids that make other animals sick give no reason to think a bird would do any better.
People Caution
No part of this plant is food, and eating it brings nausea, vomiting, and a burning throat. Swallow a real amount and it can reach the heart and breathing, so keep it away from kids 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 of what you'll find is the plain scarlet species, and honestly it's gorgeous, but a handful of selections swap in darker leaves for extra punch. Here's who's worth knowing.
Queen Victoria
Queen Victoria's got deep bronze-purple to maroon leaves that make the scarlet flower spikes really pop for a cool two-tone look.
Black Truffle
Black Truffle goes even darker, with foliage that's almost black-purple under bright red blooms, so it's got the boldest contrast in the bunch.
Fried Green Tomatoes
Fried Green Tomatoes keeps its leaves green and pairs vivid red flowers with noticeably better vigor in the garden.
How to propagate
Want more of it? You've got two easy options. Split the little rosettes it makes at the base, or just let the fine seed handle things for you.
DivisionEasy
Spring, by separating the basal rosettes (offsets) from the parent plant. · One growing season
When spring rolls around, lift the plant and gently pull the basal rosettes off the parent crown. Pop each division straight into moist, rich soil, keep it well watered, and it'll settle 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 fine seed on top 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. And in a damp spot? It self-seeds freely on its own, which is how a short-lived perennial keeps a stand going.
Myths
Cardinal flower got its name because it attracts cardinals.
Nope, the name's all about the bright cardinal-red of the blooms, the same red as the robes Roman Catholic cardinals wear. The flowers actually pull in hummingbirds and butterflies, not the bird they're named after.
Lobelia is a gentle herb that's safe to eat.
Not quite, because it's packed with lobeline and related alkaloids that turn toxic once you swallow much of it, bringing on nausea and vomiting and, in bigger amounts, more serious stuff in both people and animals. No part of this plant is safe to eat.