Yellow flag (Iris pseudacorus), Water flag, Water iris
Family
Iridaceae (iris family)
Origin
Northern hemisphere; yellow flag is native to Europe (including Britain), western Asia and north-west Africa
Water
freshwater
Maximum size
150 cm
Care level
expert
Care
Warning: Iris is a land or marsh (bog) plant, not a true aquarium plant. Kept fully under water it slowly dies; grow it emersed in a paludarium or bog garden, or with only its roots in water. Water irises are marginal pond plants that grow with their rhizomes in wet soil or shallow water and their sword-shaped leaves in the air. The best-known, yellow flag (Iris pseudacorus), is native to Europe, including Britain, western Asia and north-west Africa. It usually grows 100–150 cm tall, with leaves up to about 90 cm long and bright yellow flowers 7–10 cm across, and it copes with flooding, acidic and oxygen-poor soils and long dry spells. The roots and leaves of yellow flag are poisonous. Outside its native range it forms dense stands that crowd out other plants and is listed as invasive in many US states and in South Africa. Never release this plant or dispose of it in drains or waterways; it is invasive in some countries. Irises are temperate plants for ponds and bog gardens, not tropical tanks. Sources: Wikipedia (en.wikipedia.org/wiki/Irispseudacorus); Wikipedia, List of freshwater aquarium plant species. Checked October 2026.
Breeding
Divide the rhizomes after flowering, keeping a fan of leaves on each piece. Yellow flag also spreads by seed carried on water.
Compatibility and tank mates
Do not sell or buy it as a true aquarium plant. A good pond-margin plant with goldfish and koi, which leave the tough leaves alone.
Last updated 8 October 2026. Community-edited care guide on Aquatic-Auctions.
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