Lobelia cardinalis aka Cardinal Flower

Lobelia cardinalis, or cardinal flower, belongs to the bellflower family. This perennial grows in clumps and may be short-lived. Its native range runs from southern Canada to northern Colombia. It grows beside streams, in swamps, and in wet woods. Wet meadows and pond edges also provide suitable homes. Its name refers to the red robes worn by cardinals.

Garden plants often reach 2–3 feet (0.6–0.9 metres) tall. Some sources report heights of 4–5 feet (1.2–1.5 metres). Clumps spread about 1–2 feet (0.3–0.6 metres) wide. Upright stems bear simple leaves in an alternate pattern. The green leaves have a glossy surface and fine teeth. Their narrow shape tapers to a point at each end. Leaves often reach about 0.33 feet (0.1 metres) long. The plant loses its foliage for winter.

Red flowers grow in upright racemes at the stem tips. Each tubular bloom has two lips with five lobes. Three lobes form the lower lip; two form the upper. Flowers open from the spike's base toward its tip. Bloom runs from July through September, sometimes into October. Hummingbirds pollinate the flowers while feeding on their nectar. Butterflies also visit the blooms. Brown capsules appear from August through November. They hold many small brown seeds.

Grow cardinal flower in rich soil that stays moist or wet. It tolerates brief floods, but its soil must not dry. Sun suits plants in cool climates when water stays plentiful. In hot summers, give it shade during the afternoon. It grows in sand or loam and tolerates varied soil pH. Salt tolerance is low. Sources list USDA zones 3–9, while RHS gives UK rating H3. Winter mulch helps guard roots and reduces frost heaving. Mulch also helps keep moisture in the soil.

Use it beside ponds, in rain gardens, or in wet borders. It brings late-season height and bloom to damp woodland gardens. Deer and rabbits tend to leave it alone. Slugs and snails can damage the leaves; crown rot may occur. Cut stems back once flowering ends. Seeds, cuttings, and division offer ways to raise new plants. No edible uses are known, and swallowing it can cause poisoning. It contains lobeline and other alkaloids harmful to people and animals. Dogs, cats, and horses are at risk. Poisoning can cause vomiting, diarrhea, and changes in heart rhythm. Sources differ on skin irritation, but some warn about sap contact. Past medicinal uses do not establish that it is safe.