The iris has over 260 species in its genus. The word 'iris' comes from the Greek word for 'rainbow' and refers to the huge colour variety to be found in the showy flowers. Iris was also the messenger for Olympus and in Greek mythology, young girls were led into the afterlife by Iris.
There is a wide natural distribution throughout the north temperate zone. Irises are a hugely popular ornamental plant. The Giardino dell'Iris in Florence (Italy) hosts an annual international iris breeders' competition while the Presby Memorial Iris Gardens in New Jersey has over 10,000 plants of all colours and types.
The iris is a perennial herb and a versatile plant. A suitable variety can be found for virtually any position. The stems are long and erect. Irises may be simple or branched; hollow or solid.
To understand the groupings of the iris, it is necessary to understand the composition of the flowers. Most species have six main 'petals'. These include an outer row of three, usually drooping petals known as 'falls' and an inner row of mainly erect petals known as 'standards'. The flower stems (inflorescences) are fan-shaped. There may be one or more symmetrical flowers on each inflorescence.
Generally irises are separated into two main groups – those that grow from rhizomes (underground creeping stems) and those that grow from bulbs.
These usually have 3 to 10 sword-shaped leaves which grow in dense clumps from the base. They can be further divided into three subsections - bearded iris, crested iris and beardless iris.
The bearded iris has rows of hairs on the falls. This is the most commonly found garden iris. Bearded iris are easy to cultivate.
They all need good drainage but are adaptable to a wide range of soils and climates. Most irises love lime and will respond well to an application of lime at the beginning of winter. Superphosphate can be added in early spring at the rate of 4 ounces per square yard.
New plants can be easily obtained by lifting the old clumps and breaking off the strong outside fan growths. Leave old rhizomes if they have the fibrous roots intact. If there are no fibrous roots, the pieces will usually develop new roots when planted. Cut off half the top leaf growth to reduce transpiration and prevent loosening by the wind.
Plant after flowering so that the young plants can be well established before the next season.
The section Oncocyclus is a group of plants noted for their large, strongly marked flowers. The cushion varieties have narrow sickle-shaped leaves and must be planted in very gritty, well-drained soil. Bearded iris are mostly in the purple and blue range with yellow and white quite frequent.
There are some beautiful species among the crested iris group. These have a crested ridge or cockscomb crest on the falls. Iris japonica is a particularly fast-growing variety and produces sprays of dainty pale lavender flowers in winter and early spring. It is a useful plant for an area which is in partial shade. To propagate, simply pull away some of the outside fans from a mature clump.
The beardless iris has smooth falls and contains a number of groups. The most important are:
Iris sibirica (Siberian iris) which has narrow, almost grass-like leaves and which do best in a moist but well-drained soil. They dislike lime and respond to applications of animal manures. They are mostly blue, lavender and white.
Iris ochroleuca grows to 5 feet tall. The flowers are large and white with gold patches on the falls. It makes a striking display and is excellent for planting near water.
Iris laevigata includes many of the water-loving irises. The most commonly grown of this group is I.pseudacorus (yellow flag iris, which is easily grown and makes an attractive showing along water-courses) and I.kaempferi (Japanese iris). Iris kaempferi is not a true bog plant but likes a rich, moist, well-drained soil. It is suited to being planted at the edge of water providing drainage is good. The flowers are flat-headed but appear in a wide range of colours. An American strain of I.kaempferi produces very large flowers with at least 40 magnificent colours being available. They flower better after the first year. They dislike lime and need plenty of water.
I.unguicularis (also known as I.stylosa) has narrow leaves up to 2 feet long. It forms thick clumps and produces beautiful clear lavender-blue flowers which are flecked with gold near the centre. The flowers are sometimes engulfed by the leaves. It thrives on poor or fairly rich soils, likes plenty of sun and a fair amount of lime.
Californian irises are dainty and colourful. The species I.innominata is one of the most attractive with a long flowering period and a good range of colours. It is adaptable to most conditions and does best with plenty of lime and a position in light shade.
This section includes the Dutch, Spanish and English irises. The leaves are cylindrical and again, like the rhizomatous species, grow from the base. These plants die down in summer and are propagated from bulbils off the main bulbs. The Dutch iris in particular is a spectacular specimen as a cut flower. They do best in moderately rich soil with good drainage and some lime. Applications of superphosphate and blood and bone are helpful. The bulbs should be lifted every second year and stored in a cool, dry, well-aired place.
Some of the reticulate bulbed irises are miniatures and can succumb to too much moisture. They need a well-drained soil in a sunny spot.
Special mention should be made of the yellow iris (I.pseudacorus) which is used in water purification processes. A reed bed is constructed to hold a substrate of eg lava-stone and the roots of the iris are planted in this. The roots absorb nutrient pollutants such as that which occurs with agricultural run-off and water quality is thus improved.
Yellow Iris (above)
The iris has been a favourite with artists such as van Gogh and Joseph Mason. An unspecified species of iris is one of the State flowers of Tennessee. It is traditionally depicted as a purple iris to accompany Tennessee's other floral emblem, the purple passion-flower. The provincial flower of Quebec, Canada is the Harlequin Blueflag (I.versicolor).
With such a range of colours and such adaptability, it is no wonder that the iris is so popular with home gardeners.