Yellow flag

Yellow flag facts

Scientific name: Iris pseudacorus

Family: Iridaceae

Origin: Native

Type: Perennial

Yellow flag and our canals

A tall waterside plant with bright yellow flowers, the yellow flag can form thick beds at the edges of rivers and canals, which are valuable habitats for wildlife. It spreads through underwater rhizomes, gradually growing into dense networks.

This perennial can be known as the ‘yellow flag’, ‘yellow iris’ or ‘water flag’, and is one of only two native irises in the UK – the other being the ‘stinking iris’ (Iris foetidissima)

Yellow flags are happiest in damp soil and wetlands. However, without management, they can become an invasive nuisance.

What does yellow flag look like?

Large and sunshine-yellow, the yellow flag is a bright flower along the margins of our canals, rivers and wetlands. These plants grow tall with thin stems and grass-like long and narrow leaves. The flower is yellow with petals that fold back on themselves.

The iris’ drooping flowers are a distinctive sight – one that’s thought to have inspired the fleur-de-lis symbol.

Where to find yellow flags

Yellow flag is a widespread plant that grows best in wet conditions, spreading quickly. However, it can also survive in prolonged dry periods and copes well with shade. This water-loving plant is common on the margins of our canals, rivers and reservoirs, and although it can form dense reedbeds, it’s often found mingling amid other aquatic plants.

When to see yellow flags

The green-grey waxy foliage is visible in the spring and summer, while the bright yellow flowers bloom between May and August.      

Other plant species to look out for