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Cardinal Flower

Lobelia

The Wet Meadow Royalty: Lobelia cardinalis & siphilitica


The Snapshot

  • Common Names: Cardinal Flower (Red) & Great Blue Lobelia (Blue)

  • Scientific Names: Lobelia cardinalis & Lobelia siphilitica

  • Origin: North American Natives

  • Hardiness: Zones 3 – 9 (Incredibly cold-hardy)

  • The "Vibe": Intense, architectural, and moisture-loving; the "stoplight" of the garden.

The Tale of Two Colors


1. Lobelia cardinalis (Cardinal Flower)

The "superstar" of the genus. It produces stems of the most intense, pure scarlet red found in nature. The flowers are specifically shaped like long tubes to accommodate the beaks of hummingbirds.

  • Best For: High-drama focal points and hummingbird enthusiasts.

2. Lobelia siphilitica (Great Blue Lobelia)

The "sturdy sibling." It features dense spikes of true blue to lavender flowers. While the Cardinal Flower is a bit of a diva about its soil, the Great Blue is much more adaptable and will tolerate slightly drier conditions and heavier clay.

  • Best For: Native pollinator gardens and "cooling down" a hot summer border.

Ecosystem & Wildlife Impact

  • Hummingbird Magnet (Red): L. cardinalis is almost exclusively pollinated by the Ruby-throated Hummingbird. The bird’s forehead gets dusted with pollen as it reaches deep into the flower for nectar.

  • Bumblebee Favorite (Blue): L. siphilitica is built for the "big bees." Bumblebees must use their weight to "trip" the flower open, making it a bustling hub of activity in late summer.

  • Host Plant: Both species serve as a food source for the larvae of the Pink-washed Leafroller Moth.

Designer Tips: Where to Plant

  • The "Rain Garden" Duo: Plant the red and blue species together. The primary color contrast is visually stunning and ensures you are feeding both birds and bees.

  • Shoreline Naturalizing: Place them along the edge of a pond or a stream. They love having their "toes" near the water line.

  • The Winter Rosette: In late fall, the tall stalk dies, but the plant leaves behind a small green basal rosette (a circle of leaves at the soil line). Do not cover this with heavy mulch! The rosette needs light and air to survive the winter.

Designer Pro-Tip: Because Lobelias are short-lived (often only 3-4 years), let them go to seed! If you have open, moist soil nearby, the tiny seeds will sprout into a "carpet" of new plants for the following year. This is how you keep a "permanent" stand of Lobelia in your garden.


Stories from the Garden

"I planted Cardinal Flowers in a low spot by my gutter downspout. Every August, like clockwork, a pair of hummingbirds fights over the plants for two weeks straight. It’s better than cable TV!"

— Derrick S., Zone 5 Gardener


A Growing Story: The Seedling Surprise

A customer once complained that her Great Blue Lobelia had "moved." She planted it in a corner, but the next year it was growing in the cracks of her brick patio. We explained that the tiny seeds love to travel in rainwater. She decided to keep them there, saying the "blue cracks" were the coolest thing in her yard.

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