Beauty in the bog

Press, 29 August 1986, Page 19

Beauty in the bog

gardener’s ! DIARY

Derrick Rooney

Writing last week about ways of exploiting wet areas in a garden, I promised to describe some of the many interesting and attractive plants which thrive in wet soil. Where better to start than with the irises — one of my favourite groups of plants. Irises occur naturally in all the temperate zones of the Northern Hemisphere and in all habitats, from arid regions which see rain only a few times a year to rich, mucky swampland. In general, the wetland or "bog” irises are under-appreci-ated in gardens, though they ■ include some plants of outstanding merit. Most of the so-called "bog irises” are not true bog plants, but are subject to periodic inundation during their growing period in early summer. In the winter dormant season they require drier conditions. The Siberian irises in particular are apt to rot off if kept too wet in winter — with perhaps the exception of Iris delavayi, which is the tallest of the Siberian group and the most moisture demanding of them. The most familiar bog iris is Iris pseudacorus, the “yellow flag” of Europe and the common iris of streamsides and marshy areas which has been naturalised in many countries, including New Zealand. There used to be, and for all I know still are, thriving colonies on the banks of the Heathcote at Woolston.

In optimum conditions and heavy, fertile soil, Ins pseudacorus can grow two metres tall, but in garden conditions it seldom exceeds about 1.3 m. The ordinary wild plant has flowers of a nondescript yellow, but several selections made from it have

distinct horticultural merit. "Aurelin Gold” is lemon yellow with a brown splash, and is among the best. There is a creamy white named, I think, “Ivory Tower,” and “Bastardii” has pale yellow flowers without the brown signal. “Dwarf form” grows only 90cm tall and has deep yellow flowers. It comes true from seed. A double form, named “Plena,” has been offered by several nurseries, but I have neither seen it nor grown it. “Variegata” has wonderful foliage in spring, stout sword-shaped leaves which shoot up to 80cm or 90cm high by the end of October and are striped with pale and golden yellow. However, the flowers resemble those of the ordinary wild type and the leaves turn green later in summer. All these are adaptable plants which will grow in damp soil (perhaps where a downpipe overflows), at the poolside, or in standing water.

Iris laevigatus, from north-eastern Asia, will also grow in standing water. A smaller and more graceful plant than the yellow flag, it has large flowers which in the best forms are luminous blue. A white form is sometimes grown in gardens and comes true from seed, as does “Albo-pur-purea,” a rather special plant with white standards and broad falls patterned with lavender blue.

Over the last three centuries Japanese hybridisers have used the forms of this iris in crosses with a dryland species, Iris ensata (formerly known as I. kaempferi), to create the remarkable “Higo,” “edo,” and other strains which are known collectively as “Japanese” ir-

ises. “Purpurea” and “Rose Queen,” whose names describe their colours, are the two best known in New Zealand; they have been grown for many- years and are hardy and relatively, easygoing plants which are probably better for garden purposes than the more subtly coloured but more exacting Japanese hybrids. Modern Japanese irises have large, flat, clematislike flowers and come in a range of rich colours and pastels not found in other kinds of iris. In Japan they are often grown in specially constructed beds which can be flooded during the growing season. Planted en masse in this way, these irises have a certain appeal, but the rather formless nature of their flowers make them less

suitable for the kind of spot planting that most New Zealanders go in for.

Canterbury’s climate presents certain difficulties in the successful cultivation of these irises, whose need for moisture peaks at the time of year when our soils are at their driest. But there are ways around the problem. One solution is to plant the irises in large pots which can be semiimmersed for the summer in a shallow pool or, if you have no pool, any large watertight container. Old concrete washtubs, sunk to the rim, are ideal. You could even use an old paddling pool.When winter comes the pots of irises should be lifted out of the water and stored on a terrace, in a shadehouse, or in any cool spot outside where they will not be flooded. But remember to water them occasionally — they mustn’t dry out! Some protection from frost is desirable, not because it might harm the plants, but because it might shatter the pots.

The irises of the Hexagona group (“Louisiana irises” to gardeners) come from the south-eastern United States, and have similar requirements. Although they are swamp plants, they grow on hummocks with their rhizomes well out of the water. The efforts of hybridisers in the United States and Australia have given the Louisiana irises a boost in recent years, and these plants now come with large, flat flowers in a wonderful range of colours which rivals, and possibly surpasses, the bearded irises. Unfortunately, while they thrive in the milder and wetter western and northern parts of New Zealand, Louisianas are very diffi-

cult to manage in Canterbury. Some of the hardier kinds can be grown, though; “Clyde redmond,” which has flowers of luminous cornflower blue, is perhaps the best. A point to remember when growing Louisiana irises is that, as already noted, they are swamp plants but not bog plants. They are not suitable for growing in submerged containers in summer, in the manner of the Higo irises, because their long rhizomes would soon escape from the pots, and standing water around them would quickly rot them. They are, too, what' gardeners like to call “gross feeders.” They dislike artificial fertilisers, but thrive on manure, for which their appetite is insatiable. In the northern United States the common bog irises — and these really are bog irises — are I. virginica and I. versicolor. They are very closely related, and only an expert can tell them apart. "Gerald Derby,” with deep lavender flowers and blackish, zig-zag stems, is the best-known selection of I. virginica and is occasionally seen in gardens. Iris versicolor, in its ordinary forms, is.an interesting rather than exciting plant but is quite useful for people who want something to grow in a shallow pool and hanker for a change from the yellow flag. Far better for most garden purposes, however, is the variety kermesina, which has rosy purple rather than lavender flowers. One garden form has flowers that are very close to ruby red. This variety will grow well in quite dry conditions.