Iris pseudacorus 'Yellow Flag' - Native Iris, Pond Marginal Plant

Iris pseudacorus, known as yellow flag iris, is a tall UK native iris with grey-green, sword-shaped leaves and bright yellow flowers up to 10 cm across. It flowers from May into July and is a classic plant of wild pond and river margins.

Yellow flag iris at a glance

Botanical name	Iris pseudacorus
Common name	Yellow flag iris, yellow iris
Plant type	Vigorous, clump-forming iris; dies back in winter
Height and spread	1–1.5 m tall, spreading 1 m or more
Flowers	Bright yellow with brown veining, May to July
Position	Full sun or part shade (flowers best in sun)
Soil	Wet soil or shallow water
Pond depth	0–15 cm of water over the crown
Hardiness	RHS H7 – very hardy (below -20°C)
Native to	UK and Ireland (native wild flower)

Is yellow flag iris right for a small pond?

Only in a basket. It is vigorous, reaches 1–1.5 m and can take over a small pond if planted loose. It is best for larger wildlife ponds, lakes and stream banks.

Is it good for wildlife?

Yes. It is on the RHS Plants for Pollinators list. Bees visit the flowers and dragonflies use the leaves to emerge from the water.

How to plant and care for it

Plant in spring or summer with up to 15 cm of water over the crown. Remove seed heads before they ripen to stop it seeding around, and divide clumps every 2–3 years.

Is yellow flag iris poisonous?

Yes. All parts are harmful if eaten by people or pets, and the sap can irritate skin, so wear gloves when handling or dividing it.

Which size should I buy?

Bare-root plants (7 cm, 9 cm, 1 litre and 3 litre) arrive without a pot or compost and are the most economical way to plant a group. Potted plants (9 cm, 1 litre and 3 litre) arrive growing in our peat-free compost and give a faster display. Packs of 3 cost less per plant. The 2x Pot & Compost option is two plants supplied with pots and compost.