Iris tectorum

Iris tectorum is the Japanese roof iris, named for the old practice of growing it along the thatched ridges of Japanese farmhouses. The flowers are flat and open, lilac-blue with darker veining and a white crest ridged down the centre of each lower petal, and they sit on short stems above fans of broad ribbed pale green leaves. Flowering runs through November and December.

Roof iris suits the front of a border, a rockery, the top of a wall, or a gravel garden, and it is well matched to Japanese-style planting. The leaf fans are wide and keep their shape after flowering, so the clump still reads as a deliberate piece of planting into autumn. It grows well in a shallow wide container.

Full sun to light shade in free-draining soil. The rhizomes sit on or just under the surface and need to stay there, because burying them stops the plant flowering. This iris takes drier conditions than most and dislikes winter wet, so raised beds and slopes suit it. Suited to most New Zealand gardens. Divide clumps every three or four years in late summer, replanting the rhizomes shallowly.

Leaf fans reach around 0.3 m with flower stems to 0.4 m, and clumps widen slowly to 0.5 m across.