Plant library · Perennial Flowers
Lobelia cardinalis
Cardinal flower brings upright red flower spikes to the back or middle of a moist planting, rising to about 4 feet while keeping a narrow, clumping footprint. Its midsummer-to-early-fall bloom makes it useful where lower foliage needs a strong vertical finish later in the season. Use it in groups where its height can be viewed across the bed rather than pressed against a narrow path.
Place Cardinal Flower in consistently moist ground at a rain-garden edge, beside a stream or pond, or in a border that does not dry out. Give the clumps enough depth within the bed that the 4-foot stems do not lean into circulation space. It can stand behind shorter plants, but keep a clear sightline from a patio, window, or path to the red spikes and the hummingbirds they draw.[1]
Set plants 18 inches apart, center to center. Each clump reaches about 1 1/2 feet wide, so this spacing makes a close-knit run of foliage and flowering stems without treating the group as a solid hedge. In a mixed bed, reserve a band at least 18 inches deep for each row and avoid crowding its base with larger neighboring clumps.
Use partial sun where the soil stays wet or reliably moist through summer. Deep, fertile soil that holds moisture suits this perennial, while dry, exposed bed positions are a poor fit. In cooler northern gardens it can take more sun, but in warmer sites partial shade helps make a wet planting easier to manage.[1][2]
The red spikes occupy the planting from mid summer into early fall, providing a tall late-season layer after many earlier perennials have finished. Cut stems back after flowering, and leave enough access around the clump for that cleanup. In cold-winter areas, a mulch layer over the root zone helps limit winter heaving and also conserves moisture.[1][2]
Cardinal flower is a relatively short-lived clump-forming perennial, so avoid making a single plant the only vertical feature in a long border. Repeat it in several moist pockets or include other lasting structure nearby. Slugs and snails can damage the foliage, making close inspection easier when plants are reachable from the bed edge.[1]
Editorial content updated 2026-07-20.