With varieties that flower up to eight months of the year, irises are for everyone, says Gillian Vine.
With some 200 hundred species and thousands of cultivars, most of them good for cutting, irises have a place in almost every garden.
Irises are divided into two main groups, bulbous and herbaceous, or rhizomous. Each of those groups has numerous subdivisions.
The bulbous irises include the familiar Dutch, Spanish and English types (the xiphium group), as well as the small reticulatas and I. bucharia.
Rhizomatous irises have fleshy rhizomes and usually sword-like leaves arranged in a fan shape.
This group is much larger and includes the bearded irises, all of which grow well in the South.
Some start flowering by June, making them invaluable for winter and early-spring colour.
Rhizomous I. unguicularis puts out a succession of soft blue flowers from as early as June and, if dead heads are left, they produce orange berries, giving a second colour hit.
From the end of July, bulbous reticulatas (I. histrioides) begin blooming. Flowers are usually blue or purple, but there is a related species, I. danfordiae, which has yellow flowers.
Other low-growing irises include I. bucharia, probably the easiest to grow of the sometimes temperamental Juno group; and I. innominata, which has grassy leaves, quickly grows into good-sized clumps and has been bred in almost every colour in the iris spectrum, from white through gold to purple. These small plants add late winter or spring cheer before the Dutch irises come into bloom.
Dutch irises and the Spanish and English irises that follow are ideal for providing a succession of flowers suitable for picking from spring until Christmas. Less familiar is I. juncea, which has vivid golden-yellow flowers.
All the bulbous irises do best in a sunny spot with well-drained soil that is slightly alkaline, so some lime may be needed. Do not water them in summer, no matter how dry they become, as this baking is essential for their health.
The bearded irises also need summer baking, which is why they thrive in Central Otago. The dwarf forms flower first, then the intermediate and tall varieties. Most have finished flowering by the end of November, overlapping with the sibericas and then - in a final flourish - the Japanese irises (I. ensata) produce their large, flat flowers in January.
In contrast to most irises, sibericas and Japanese varieties need damp feet throughout the summer, so do best beside a pond or in a boggy spot. They generally perform best in a sunny situation and, although I. sibirica tolerates semishade, it is happiest with sunshine for half the day.
With so many to choose from, the only thing lacking is an iris with red flowers, something every breeder would love to achieve
Tip
If growing bulbous irises, such as reticulatas and Dutch varieties, in pots outdoors, do not stand pots in saucers but put them on bricks or use decorative feet. This helps prevent the soil becoming waterlogged, which causes bulbs to rot.
Don't grow this iris
Iris pseudocorus, the European yellow flag iris, is one of the "don't grow" plants on the National Pest Plant Accord list. The accord is an agreement between the Nursery and Garden Industry Association (NGIA), regional councils and government departments involved in biosecurity. Plants on the list are not allowed to be sold, propagated or distributed in New Zealand. For the full list, visit www.biosecurity.govt.nz/pests-diseases/plants/accord.htm
I. pseudocorus dies down in autumn, then fresh sword-like leaves emerge in spring. In late spring or early summer, the plant produces yellow flowers that are followed by capsules containing numerous brown seeds.
Poisonous to humans and animals, the yellow flag's rhizomes form dense floating mats, and the plant squeezes out native species that grow on margins of water bodies, including estuarine areas. It can also invade flood-prone pasture.
