Wild Iris Dietes grandiflora

The large wild iris makes a strong upright clump of broad, dark green, strap shaped leaves arranged in flat fans, and it holds that form all year without collapsing or going untidy. The flowers are the size of a garden iris, white and marked in yellow and violet, and they come in flushes rather than one continuous season, often opening a few days after decent rain. It is the plant specified for mass planting in car parks, medians and commercial beds, largely because it survives being ignored.

Mass planting that survives neglect

Growth is moderate, and water requirements drop away to low once the clump is established, which is the basis of its reputation in unirrigated commercial planting. It tolerates sand, clay, coastal exposure and reflected heat off paving, and it copes with both frost and subtropical humidity. In mass planting, set plants close enough that the fans knit into a continuous mat and weeds cannot get a start. In a domestic border it works equally well as a repeated accent.

The failure mode is the pruning. Flowers are carried on woody stems that are used again the following season, so cutting those stems off along with the spent blooms removes next year's display. Take them out only once they have gone brown and brittle. The second half of the same mistake is shearing the whole clump like a hedge to tidy it, which leaves brown cut ends across every leaf and takes months to grow out. Remove individual old leaves at the base instead. It also seeds freely, so it is not a plant for gardens backing onto bushland or waterways in coastal New South Wales and Queensland.

Grandiflora beside the yellow one

The plant it is most often confused with is Dietes bicolor, and the two are not interchangeable. Bicolor is shorter and finer, with narrower, paler green leaves and soft yellow flowers blotched dark maroon, and it reads as a lighter plant in a bed. Grandiflora is taller, broader in the leaf and heavier in the clump, with larger white flowers, and it works as a genuinely structural plant. Use grandiflora where you need presence at the back of a border or a substantial mass. Use bicolor for finer texture in a narrow bed. For bold foliage in shade rather than exposure, Acanthus mollis is the other direction. More in the low maintenance range.

The stems you must not cut

Deadhead by snapping off the spent flower and its seed capsule while leaving the stem standing, which stops it seeding and keeps the flowering wood for next year. Cut whole stems out at the base only when they are dry and brittle. Feed in early spring with a general fertiliser, water it in, and give an established planting a deep soak before a hot dry stretch to keep the leaf tips green. Divide congested clumps in autumn or early spring if the centre has thinned, cutting down through the tough rhizome with a spade rather than trying to pull a clump apart by hand.

Choosing a size

This plant is available in 6 sizes, from 75mm up to 5L, priced from $16.95 to $29.95 per plant. The size shown is the pot the plant arrives in, which is the rootball, not the height of the plant. These are younger plants, priced for planting in quantity, and they establish quickly once in the ground. Not sure which to choose? Read our guide to low water gardens.