Yellow flag iris heralds summer’s arrival: Casual Gardener

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One of my favourite flowers at this time of year is the yellow flag iris, Iris pseudacorus, an understated Irish native perennial with both architectural and biodiversity value.

It’s probably not that common in people’s gardens but if you have a pond or bog garden then you should have some yellow flag iris – and to be fair, anybody who has the room should have a pond or a bog garden. If space is limited, they’ll be happy in a half-barrel .

It’s not a plant you’ll see too much of on the eastern side of Ireland . You need to go west, where the fields are boggier and less fertile, and here you’ll find the native flag iris in abundance; on verges, in ditches and anywhere its roots can find moisture, whether on damp ground or fully immersed in water.

Its bright, buttercup-yellow flowers are great for bees, producing relatively large amounts of nectar. However, there’s rarely a profusion of flowers with flag iris, so you’ll need them in substantial numbers to be effective.

It’s also a favourite habitat for dragonflies and damselflies, who will lay their eggs at the water’s edge. The flies’ larvae will then use the iris’s sword-like leaves to climb out of the water, where they molt their exoskeletons and transform into adults.

While mildly toxic for pets if digested, the yellow flag was nonetheless deployed in many folk remedies, with the roots used for toothache and the heated leaves applied to the skin to cure mumps. The flowers can also be used to create a yellow dye and the root a black dye.

In a pond situation, the yellow flag can become quite invasive, often thriving by drawing nutrients from the water. Every so often it’s therefore necessary to get in the water and cut it back before it encroaches too far across the surface.

Congestion, like propagation, is easily addressed and best done in late August, at a time when you wouldn’t dream of disturbing any other plant. Your approach doesn’t need to be particularly sophisticated - in my experience, slicing the rhizomes with a spade and pulling them apart is as good as anything.

Each flower of the iris boasts three erect standard petals with three, known as ‘falls’, below curving downwards. The name iris comes from the Greek for ‘rainbow’ and the variety of flower colours available reflects the entire spectrum.

There are around 300 different varieties of iris available, with bearded iris the most common. The tall (approximately two-and-a-half feet-plus) bearded iris flower in May and last around six weeks. Intermediates are smaller and flower earlier, while those coming in under one foot are regarded as dwarfs and flower around April.

The rule of thumb being the smaller the plant, the earlier it flowers.

Much successful iris maintenance is counter intuitive. For instance, plant bearded iris with the upper part of the rhizome partially exposed, so it gets a baking in the summer sun, which helps get the rhizomes ready for next year’s flowers.

If you’re after a more daring variation on the native iris, recommended varieties include ‘Edith Wolford’ (with yellow standards and lilac falls), ‘Obsidian’ with its dark purple - almost black - flowers and the dark blue blooms of ‘Titan’s Glory’.