It grows as a perennial plant, usually as a subshrub though it can take any form from a herb to a shrub depending on conditions; the plants are usually woody at the base. The leaves are generally 5–8 cm in length. Their form changes from the bottom to the top of the plant, the lower leaves being petiolate while the upper leaves are sessile. The leaves grow in opposite pairs and are oval or lanceolate in shape. The plant flowers profusely, and though the individual flowers are small (no more than 2 mm), the inflorescences are large and showy. The flowers are small in rounded clusters each with 5 fused petals and a spur.
The most typical colour is a brick red or purplish red, but colours include deep crimson, pale pink, and lavender. Centranthus ruber ‘Albus’ (about 10% of individuals) has white blooms. Flowering takes place in early summer and, in cool summer areas, continues sporadically throughout the summer and into fall.