Less familiar irises worth cultivating

Press, 7 October 1988, Page 10

Less familiar irises worth cultivating

GARDENER'S I DIARY

Derrick Rooney

I get the impression that most people’s experience of irises is limited to a few of the tall bearded types and maybe some innominatas and one or two of the older Higo and Siberian types. The quality of all these has been improved immensely — for garden purposes — by plant breeders in recent years. Since the boarded irises peaked at perfection — or what passes for perfection — in the 1970 s there has been increasing interest among breeders in the Siberian and Pacific Coast irises.

The Siberian irises particularly have been vastly improved in the last decade or two, with the development of tetrapioid varieties, bicolours, ruffles, and flares. Most of the older Siberian Irises were in shades of lavender or purple, but breeders have developed large-flowered creams, whites, and now yellows. Since they thrive in New Zealand conditions and require a minimum of maintenance — an annual mulch, feeding with fertiliser, and little

or no spraying — they should grow rapidly in popularity in the near future.

Unlike bearded irises, which require biennial lifting and dividing, Siberian irises can remain untouched for many years and will continue to grow and flower. Even if you don’t feed and water them they will plug on, although the flowers will of course be smaller and sparser. Pacific Coast irises are also low-maintenance plants — especially lowmaintenance, in view of the fact that irrigating them in summer is unnecessary and may even be harmful.

They were developed from a cocktail of Western North American species and flower in late spring — the first are opening now in my garden. They come in all the standard iris shades (true red remains absent, but breeders are working on it) and some have flowers prettily veined and marked in contrasting colours.

Numerous named varieties are listed in American publications (but at a price); however, in New Zealand PCIs, as they are known, are usually offered as unflowered, mixed seedlings. They can be divided, with care and perfect timing, but seed-

lings generally make better plants. Their needs are simple: good drainage, light, humusy soil, and full sun or semi-shade. If you get things right, then leave them alone, they will show their approval by seeding spontaneously in the garden.

Most of the seedlings will be worth growing — if you start with good parents. Mostly they set seed fairly freely, but this doesn’t seem to debilitate them.

Similar conditions — but with more summer

moisture — suit the Evansia irises: I. tectorum and I. milesii for the border, I. cristata and J. lacustris for the rock garden. The iatter two are much confused in gardens and in the nursery trade, and I would not mind a buck for every time I've been sold the first as the second. It’s never the second as the first, oddly enough; I think I. lacustris must actually be quite rare. Both have short fans of broad, green leaves and dainty little lavender-blue flowers but there are botanical differences that are not perhaps apparent to the non-botanical eye.

For the ordinary gardener, perhaps the easiest clue to the identification of the two is that I. cristata always spreads by long, thin rhizomes on top of the ground, making big loose clumps, whereas I. lacustris spreads by underground rhizomes and forms very close clumps.

Iris tectorum is known as the Japanese roof iris, although it originated in China and as far as I know is not in reality grown on anybody’s roof. It is very prone to virus but seems to suffer no ill

effect from it, beyond a yellowing of the leaves. The large, flat flowers of the common type are lavender blue with darker blotches. I have a seedling or two of a Taiwan form which is said to have larger, self-coloured flowers, but it has yet to flower. There is a white form — lovelier than the blue — that comes true from seed (the two don’t seem to interbreed and produce intermediates, which is both interesting and unusual). A tetrapioid white form has recently been introduced to cultivation. Iris milesii has leaves resembling those of a bearded iris, and distinctive green rhizomes, banded with yellow on the old leaf-scars. It grows taller than its cousin (up to 60cm, compared with up to 30cm) and has smaller flowers, which may be why it is less popular. It’s important to get a good form, because there are some poor ones with very small flowers, and not many of them. These are, by and large, no-fuss plants requiring a minimum of fertilising and spraying, but it’s important to realise that they are not low-mainten-ance plants in the same league as the Siberians and the PCIs. The Evansias tend to exhaust the soil they grow in, and must be lifted, divided, and replanted in fresh soil every couple of years. As with bearded irises, the time to do this is a week or two after flowering finishes. Split them up, if you can, into fans consisting of three short rhizomes and replant them firmly. Water them in well afterwards. Throw away the old, tired rhizomes.

Siberian and Pacific Coast irises are low-maintenance plants