Marginal pond plant
Cardinal flower
Lobelia cardinalis L.
A clump-forming, erect perennial used on pond margins and in bog gardens, producing bright red summer flowers. Requires reliably moist, fertile soil and is classed H3 for hardiness.
PLANT PROFILE
About Cardinal flower
Cardinal flower (Lobelia cardinalis) is an erect, clump-forming herbaceous perennial commonly used at pond edges, in bog gardens and in rain-garden plantings. RHS lists it among plants suitable for pond and marginal planting and in pond-propagation guidance. Plants typically reach up to about 0.5–1.0 m tall with a narrower spread, making it a good vertical accent at the water’s edge. Flowers are produced in summer on tall stems and are noted in RHS material as bright red, though specific month ranges are not given in the supplied sources.
Cultural needs from the RHS guidance are straightforward: grow in deep, fertile, reliably moist soil in full sun to partial shade and situate it at pond margins or in consistently damp soil. The species is assigned RHS hardiness rating H3; some forms may require winter frost protection in colder parts of the UK. RHS also warns the plant can be susceptible to slugs and to crown rot, so avoid prolonged waterlogged crowns and monitor for slug damage. Cut back after flowering to tidy plants and encourage fresh growth. RHS flags the species as potentially harmful if eaten and as a skin irritant, so handle with care and keep away from animals that might ingest it.
Propagation and maintenance are well supported by RHS: it is listed among pond plants that are easy to propagate. Propagation methods given in the supplied sources include seed (sown in gentle heat as soon as ripe), bud cuttings in late summer, and division. The RHS pond-propagation quick facts describe propagation difficulty as “Easy.” The supplied sources do not give numeric planting or water-depth figures in centimetres, do not list it as an oxygenating submerged plant, and do not provide explicit wildlife-attraction claims in the pages consulted. GOV.UK guidance pages searched did not identify Lobelia cardinalis as a listed invasive species or subject to Schedule 9 restrictions in the material reviewed, but for definitive legal advice check current statutory lists for your UK nation.
POND SUITABILITY