Yellow flag iris Iris pseudacorus
Yellow flag iris (Iris pseudacorus) is a deciduous perennial flowering plant in the Iridaceae family, native to Europe, western Asia and North Africa. It grows 90 cm–1.5 m (35 in–4.9 ft) tall and 50 cm–1 m (20 in–3.3 ft) wide, wants full sun and high water, and is hardy to about -32 °C (-26 °F). Space plants about 60 cm (24 in) apart.
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Yellow flag iris at a glance
| Type | Perennial flowering plant, deciduous |
|---|---|
| Family | Iridaceae |
| Mature height | 90 cm–1.5 m (35 in–4.9 ft) |
| Mature spread | 50 cm–1 m (20 in–3.3 ft) |
| Spacing | 60 cm (24 in) centre to centre |
| Sun | Full sun, at least 5 h of direct sun a day |
| Water | High; drought tolerance low, waterlogging tolerance high |
| Soil pH | 4.5–8 |
| Cold hardiness | About -32 °C (-26 °F) once established (roughly USDA zone 4) |
| Heat stress | Likely above about 34 °C (93 °F) |
| Flowering | from about May for 4–6 weeks (northern hemisphere; later in cold climates, earlier in warm ones) |
| Wind tolerance | Moderate |
| Pollinator value | Moderate |
| Edible | Not grown as food |
| Native to | Europe, western Asia and North Africa |
| Common in gardens of | 🇬🇧 United Kingdom, 🇮🇪 Ireland, 🇫🇷 France, 🇩🇪 Germany, 🇳🇱 Netherlands, 🇵🇱 Poland, 🇸🇪 Sweden, 🇳🇴 Norway, 🇷🇺 Russia, 🇹🇷 Turkey, 🇲🇦 Morocco, 🇺🇸 United States, 🇳🇿 New Zealand, 🇿🇦 South Africa, 🇦🇷 Argentina |
| Invasive in | USA and Canada (restricted in several states), New Zealand, South Africa, Argentina: check local rules before planting |
Is Yellow flag iris toxic?
- People: moderately toxic
- Cats: moderately toxic
- Dogs: moderately toxic
- Parts: rhizomes, leaves, sap
Rhizomes and leaves are poisonous to people and livestock, and sap can irritate the skin; wear gloves when dividing it.
If a child or pet may have eaten part of a plant, call a poison centre or vet straight away.
Companion planting: what to grow with Yellow flag iris
No well-documented helpful pairing. Group it with plants that like full sun and high water.
Questions about Yellow flag iris
- How far apart should I plant Yellow flag iris?
- About 60 cm (24 in) apart, centre to centre. A mature plant spreads 50 cm–1 m (20 in–3.3 ft).
- Does Yellow flag iris need full sun?
- Full sun: at least 5 hours of direct sun a day.
- How much water does Yellow flag iris need?
- High water. Drought tolerance is low and waterlogging tolerance high.
- How cold-hardy is Yellow flag iris?
- It tolerates about -32 °C (-26 °F) once established, roughly USDA zone 4.
- When does Yellow flag iris flower?
- From about May for 4–6 weeks (northern hemisphere; later in cold climates, earlier in warm ones).
- Is Yellow flag iris poisonous to cats and dogs?
- For cats it is moderately toxic; for dogs moderately toxic; for people moderately toxic. Rhizomes and leaves are poisonous to people and livestock, and sap can irritate the skin; wear gloves when dividing it.
- What grows well with Yellow flag iris?
- There is no well-documented companion pairing for Yellow flag iris. Group it with plants that like the same sun (full sun) and water (high).
Sources and evidence
Evidence grade A (A: strong evidence).
- Plants of the World Online (taxonomy, native range), Royal Botanic Gardens, Kew
- RHS Find a Plant (plant profiles and growing guides), Royal Horticultural Society
- Wildflowers and meadows, Plantlife (UK)
- CABI Invasive Species Compendium, CABI
Notes and assumptions
- A marginal: it stands in shallow water at the edge of a pond or in wet mud; divide clumps every few years.
- Native to British and Irish wetlands, and far too large for a small pond: it clumps fast and floating seeds spread it along waterways. Keep it in a basket, and away from wild water where it is not native.
Reference values for planning, not horticultural, veterinary or medical advice. Varieties, soils and local climates differ: check with a local nursery or extension service.
Related plants
- Bearded iris Iris germanica
- Japanese iris Iris ensata
- Siberian iris Iris sibirica
- Dutch crocus Crocus vernus
- Gladiolus Gladiolus x hortulanus
- Freesia Freesia refracta hybrids
- Montbretia (crocosmia) Crocosmia x crocosmiiflora
- African iris Dietes grandiflora