Iris Flowers and Varieties
Most people immediately think of irises as the large flamboyant flowers, in all manner of wonderful colours, which grace the garden in May and June. These are the flag, German or bearded irises which have been so intensively bred and selected that the number of varieties now available is quite bewildering. Yet they are only one section of an immense family of herbaceous perennials and bulbs — some are quite tiny plants suitable for rock gardens, while others are tall and suitable for wet places or the shallow water at the edge of lakes. Collectively, they have a flowering season extending from January to July.
The ‘bearded’ flag or German irises all make substantial rhizomes, that is, thick stems which lie flat on the ground and make roots from their undersides. ‘Bearded’ means that on the centre of each of the three broad outer segments of the flower, the ‘falls’, there is a line of short coloured filaments like a beard. ‘Flag’ refers to the size of the three upstanding central segments of the flower and ‘German’ to the fact that Iris germanica was one of the important early parents of these hybrids, although other species have also been involved.
For many years the bearded iris has been a cult: societies have been formed to promote it, shows organized to display it and books devoted to it. Thousands of varieties have been raised and named, the size of the flowers has been greatly increased, their placement on the stems improved and their colour range extended to include many shades that are found in few other plants except orchids.
As usual, advance has not been gained without some loss. Some of the varieties are so tall that they require staking, some are more prone to disease than the wild species and most require more care. As a rule they benefit from being dug up and divided every second or ‘third year which provides an opportunity to cut off a lot of the old half-dead rhizome that has formed in the centre of the clump and to replant the vigorous outer portions in fresh. The best time to do this is in late June or early July as soon as the flowers fade, for it is shortly after this that the rhizomes start to make new roots.
Bearded irises like sunny places and fertile, well-drained soils containing some lime. Plant the rhizome, which need be no more than 10-15cm (4-6in) long, covered just enough with soil to keep the plant firm and erect while it is establishing itself. After a while, the rhizomes will work themselves out on top, but do not attempt to cover them again. They benefit from annual feeding in spring with a good general fertilizer, and an extra dressing of superphosphate of lime at 50g (1-3/4oz) per square metre can be given in July.
Enthusiasts usually grow bearded irises in beds by themselves, and even make iris gardens, but they can perfectly well be mixed with other plants so long as the irises are not overrun or deprived of light and can be lifted and replanted in fresh soil every few years.
A great many iris varieties flower in June and are from 75-100cm (30-40in) high but there is also a race of smaller, intermediate bearded irises which flower in May. They do not require staking and are often easier to accommodate with other. They usefully extend the iris flowering season but they are neither so numerous nor quite so magnificent as the June-flowering varieties.
Bulbous irises include small winter-flowering species, such as the blue Iris histrioides, violet-purple Iris reticulata and yellow Iris danfordiae, as well as much taller May and June-flowering kinds such as the Spanish irises derived from Iris xiphium and the English irises derived from Iris xiphioides . These tall kinds make excellent cut flowers, while small early-flowering bulbous irises look good inand raised rock beds where they benefit from the good drainage provided by a porous, rather gritty soil. They are best planted in September 58cm (2-3in) deep, but as much as 12cm (5in) for I. Danfordiae.
Fibrous-rooted irises include such very different species as the winter-flowering Algerian iris, Iris unguicularis (still more familiar to many gardeners under its old name Iris stylosa), which likes a warm, sunny, well-drained place, and the summer-flowering Siberian iris, Iris sibirica, which enjoys moist soil and is never happier than when planted at the water’s edge.