The cardinal flower (Lobelia cardinalis) is a perennial plant from North and Central America. It features spikes of red flowers on leafy stems up to 5 feet tall.
As a longtime gardener, I recommend adding this flower to your garden for two main reasons: it adds a stunning splash of color and it attracts pollinators like hummingbirds and butterflies, making it one of my favorite ornamentals.
I’ve learned that cardinal flowers need specific care to maintain their vibrant appearance and health.
Below are my tips to help your cardinal flowers thrive.
Quick Cardinal Flower Insights
- Scientific Name: Lobelia cardinalis
- Other Common Names: Lobelia, Cardinal flower, Red Bay
- Mature Size: 2-5 feet tall, 1-2 feet wide
- Native Area: Native to North and Central America
Lobelia cardinalis is better known by its common name: the Cardinal flower. This showy species is part of the bellflower family (Campanulaceae) and is widely distributed.
The plant gets its common name from its brilliant red flowers, which resemble the vestments worn by Roman Catholic cardinals. Its leaves have a toothed margin.
I love this species for its bright red, tube-shaped flowers, which bloom from late summer to early fall. It’s great for adding color to a landscape and attracting bees and hummingbirds.
The Cardinal flower grows throughout North and Central America, southeastern Canada, Mexico, and northern Colombia.
This native clump-forming perennial has lance-shaped dark green leaves that form basal clumps and tall flower stalks with tubular flowers. Its flowers are typically scarlet red, but other cultivars have rose-pink flowers.
These plants thrive in moist areas like wet woods, streambanks, ponds, swamps, and marshes.
Known Pollinators
Hummingbirds, butterflies, and bees all love Lobelia cardinalis.
These flowers are perfect for hummingbirds’ long beaks to reach the sweet nectar. But butterflies and bees also find them tasty!
Cardinal Flower Needs
In my experience, Lobelia cardinalis will thrive with just a bit of care. The key to seeing this species’ brilliant red, trumpet-shaped flowers is balancing sunlight, water, and wet soil.
Sunlight Preferences
I recommend growing cardinal flowers in full sun to partial shade, but they are easily grown in filtered light.
Whether you have potted plants or not, give them 4-6 hours of sunlight each day to help them bloom.
Place them in a spot with morning sun and afternoon shade. This will give them enough light to fuel those gorgeous blooms but keep them cool during the hottest part of the day.
They can also tolerate full sun in cooler regions but may require extra watering to maintain consistent moisture.
Climate and Temperature
Lobelia cardinalis are typically found near water sources and thrive in areas with high humidity and moisture.
These moisture-loving plants prefer temperatures from 32 to 95°F (0 to 35°C). That’s why they do great in USDA zones 3-9.
They can handle some heat or even full sun, but not for too long. Cardinal flowers in colder areas will tolerate direct sunlight better.
I suggest closely monitoring them during heat waves. Give them extra water as necessary.
Watering Frequency
Lobelia cardinalis thrives in consistently moist soil. They naturally bloom in wet soil, so I advise not letting your garden dry out.
Water these plants regularly to keep the soil damp but not waterlogged.
Increase the watering frequency during dry periods to ensure they stay hydrated—especially if it’s hot and sunny.
But they can hold out a little longer if they get at least some partial shade in your garden.
A good rule of thumb for potted and outdoor plants in part shade is to give them about 0.8 cups of water every nine days.
Ideal Soil Types
I recommend planting your cardinal flower in rich, well-drained ground. If you want your Cardinal flowers to self-seed, try planting them in moist soils.
Loamy soil is ideal for this plant. It can also tolerate various pH levels, from alkaline to acidic.
You can plant them in the following areas:
- Along borders
- Rain gardens
- Along stream or pond edges
Feed and Fertilizer
Give your Cardinal plants compost or a granular fertilizer when they begin to bloom.
I’ve found that this flower species usually blooms in two years, first forming a big rosette. Allow the cardinal plant to self-seed in your garden for continuous growth.
Lobelia cardinalis benefits from a balanced, slow-release fertilizer applied in the spring to help it continue growing.
However, avoid over-fertilizing your flower. One-time application is usually enough for the entire growing season.
Overwintering Your Cardinal Flower
Your cardinal flower can handle slight winter chills, especially in zones above 3. Regardless of temperatures, they will come back strong next spring.
But if you live somewhere with harsher winters, I recommend covering them with mulch before the first frost.
This insulation helps to retain soil moisture and protect the root system from freezing temperatures.
Less winter protection is needed in milder climates, but mulching can still benefit overall soil health.
How to Grow Cardinal Flowers From Seed
To grow a cardinal flower from seed, sow the seeds indoors 8-10 weeks before the last frost.
Sprinkle the seeds on a damp seed-starting mix, give them some light, and keep things warm and moist.
In several weeks, you’ll notice tiny seed sprouts, and then you can transfer them to an outdoor garden in a larger container when the weather becomes warmer.
Space the young plants 1-2 feet apart.
Since Cardinal flowers are short-lived perennials, the parent plant will last a few years but can self-sow if the seeds have good seed-to-soil contact.
Propagation Tips
Besides propagating through seeds, you can also propagate a cardinal flower through division or cuttings.
- Division: This is best done in spring or fall. To divide Lobelia cardinalis, carefully dig up the parent plant and separate the root clumps. Replant them immediately.
- Cuttings: Cuttings can be taken in late spring. Take 4-6 inch stem segments, remove the lower leaves, and place them in a moist rooting medium until roots develop.
Pruning
I recommend pruning your plants to remove dead or damaged parts and encourage growth. Pruning also improves air circulation, reducing the risk of diseases.
The cardinal flower should be pruned from early spring to late fall to coincide with the plant’s active growth period.
NOTE: Pruning may prevent the plant from self-seeding, which may impact next year’s growth.
Deadheading
Deadheading, or removing spent flowers, encourages the plant to produce more blooms.
For a Lobelia cardinalis plant, deadhead regularly throughout the blooming season to extend the flowering period and keep the plant looking its best.
After the flowering period, cut back the stems to promote bushier growth.
Notable Cardinal Flower Varieties
Lobelia cardinalis is a stunning native plant known for its vibrant red flowers.
However, if you’re looking to diversify your garden with more color, here are several notable varieties to consider.
- Great Blue Lobelia (Lobelia siphilitica): The great blue lobelia, sometimes called the blue cardinal, has blue or whitish flowers.
- Queen Victoria: Vivid red flowers on striking burgundy stems.
- Angel Song: Creamy and salmon-colored flowers for a whimsical touch.
- Black Truffle: Crimson flowers with nearly black, dark purple foliage.
- Rosea: Delicate pink blooms for a softer touch.
- Alba: Pure white flowers for a serene look.
Cardinal Flower Issues
While Cardinal flowers make for a beautiful garden, remember that these plants are toxic.
The plant contains 14 alkaloids similar to nicotine, which are only harmful if eaten in large quantities. Ingesting parts of the plant can cause vomiting, sweating, pain, and even death.
Always handle the plant carefully and keep it out of reach of children and pets.
Disease
In my experience, Cardinal flowers are prone to two main diseases: Rust and leaf spots.
Rust appears as orange or brown pustules on the underside of leaves.
Treat your plants by thinning them out to improve air circulation. Remove infected leaves and debris around the plant base, and use fungicides if necessary.
Leaf spots manifest as brown or black spots on leaves.
Similar to rust, it can be addressed by improving air circulation and removing infected foliage around the plant. Fungicides can be used if the problem persists.
In both cases, keeping the area clean and watering at the base of the plant can help prevent these diseases.
Pests
While generally resistant to pests, Lobelia cardinalis can occasionally attract aphids, slugs, and snails. Regular inspection and prompt removal are key to keeping these infestations under control.
- Slugs and Snails: These pests feed on leaves, leaving ragged holes. Handpick and remove them at night when they’re most active. Use natural deterrents like crushed eggshells or beer traps.
- Aphids: These sap-sucking insects can cause stunted growth and damage leaves. Planting other perennials in your garden will encourage beneficial insects like ladybugs, which prey on aphids. You can also use insecticidal soap spray.
The cardinal flower thrives in moist soil and can stabilize a landscape with its fibrous roots. I recommend pairing it with purple and blue flowers, along with many other perennials.
It blooms in early summer to late summer and is excellent for attracting pollinators like butterflies and hummingbirds.
With proper care, these stunning perennials can be a focal point in the garden all year round.
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