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24 November 2009
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Bearded iris

Iris

Irises are named after the Greek goddess of the rainbow and grow wild throughout the northern hemisphere, from high Himalayan bogs to arid Greek hillsides and the banks of British canals.

In this article

Irises are useful upright perennials that can be grown in many different areas. Choose well and you'll have irises in flower for six months, from November to June. You'll also get a wide range of colours, from rich blues to flashy yellows, and extraordinary combinations such as butterscotch yellow and violet. Many also have beautiful, intricate patterns.

Botanists divide irises into two key groups: rhizomatous, which have rhizomes on or just beneath the soil, and those grown from bulbs. The first group divides into two further sections, beardless and bearded.

The best way to decide which ones you want to grow is to visit a specialist nursery and check the colours and growing conditions.

Beardless border irises

Pacific Coast irises have a wide, typically quiet, range of colours with attractive veining. Other main kinds in this group are Siberian and water irises.

• I . 'Broadleigh Carolyn': classic Pacific Coast iris with clear blue flowers. Has been given the Royal Horticultural Society Award of Garden Merit (AGM).
• I. graminea : also called the dwarf plum tart iris - because it really does smell of hot plum tart - this Spurian iris has slender, deep purple flowers almost hidden by narrow leaves. If grown in clumps, it flowers so abundantly there are plenty of blooms to cut for indoors. Has been awarded the AGM.
• I. orientalis : another Sprurian iris, this is robust and reliable, with slender yellow and white flowers, and ideal for dry, sunny borders. Has been awarded the AGM.
• I. sibirica : one of the easiest irises to grow, forming a dense clump of slender leaves with a neat, tidy shape and a mass of dainty, early summer flowers in blue, violet, white or veined. 'Butter and Sugar' is creamy yellow and white, while 'Papillon' is pale blue. I. sibirica and 'Butter and Sugar' have been awarded the AGM.

Border bearded irises

Many of these date back to the 17th century, but some ( I. germanica , I. florentina and the variegated form of the scented I. pallida ) are just as popular today.

• I. germanica : relativelysmall, latespringflowers, inaarichshadeofpurple.

Pond plants

Irises include some of the easiest and most attractive marginal pond plants, the majority of which can also be grown in damp borders.

Some of the most dramatic are the modern Japanese hybrids, which have complicated markings.

They tend to be vigorous and are easy to propagate by division in early spring (rather than the more usual August).

• I. ensata : beardless Japanese iris with purple or reddish-purple mid-summer flowers. 'Rose Queen' is soft pink. Both have been awarded the AGM.
• I. laevigata : beardless broad-leaved iris with early and mid-summer blue flowers. 'Variegata' has attractive green-and-white striped leaves topped with pale purple flowers and is the only iris that needs to be grown in water all the time. Both have been awarded the AGM.
• I. pseudacorus : the familiar yellow flag iris of wild water meadows is much too vigorous for most gardens if planted in wet ground beside a natural pond, but is more manageable in a border where the soil isn't too dry. The golden leaves of 'Variegata' are particularly beautiful in early spring. Both have been awarded the AGM.

Winter and spring interest

Although irises are principally associated with full sun, some thrive in cooler conditions. They're free flowering in winter, providing a perpetual succession of blooms.

• I. foetidissima : called the 'roast beef iris' after the smell of its crushed leaves, this is one of the most adaptable plants regarding soil or position, and is often found in hedgerows in southern England. It has slender leaves and produces insignificant brownish flowers in April. In late autumn, the plump seed pods open to reveal red seeds that remain on the plant into the new year. 'Variegata' has striking white markings but is prone to rust if not divided regularly. Both have been awarded the AGM.
• I. japonica : slightly tender iris that likes an area in front of a sunny, sheltered wall. Produces a broad fan of leaves and, in late spring, exotic pale blue or white frilly flowers, dramatically splashed with purple with an orange crest. 'Ledger' is reputedly the hardiest form. 'Variegata' has attractively striped green and white leaves. I. japonica and 'Variegata' have been awarded the AGM.
• I. unguicularis : whenever the temperature rises above freezing for a few days, this will produce late winter and early spring flowers. 'Mary Barnard' is the most free-flowering form. It has slightly narrower leaves than the ordinary type and starts producing rich purple flowers early in November. In cool springs, it may continue into April, although it usually stops in March. 'Walter Butt' has scented, almost grey flowers and might start flowering in late autumn.

Dwarf irises

There's a wide choice for the front of the border or rock garden, although some can be tricky. One of the best is:

• I. cristata : tiny 6cm (2in) high plant, which gradually spreads to form small patches. Has relatively large, rather flat, blue or white crested late-spring flowers.

Site and soil preferences

Irises generally prefer well-drained soil, the exception being the water-edge varieties. Add grit and humus to open up heavy clay soils.

Pacific Coast irises require neutral to acid soil and, unlike most irises, flower equally well in partial shade and full sun.

I. cristata prefers humus-rich soil in partial shade and is best divided just after flowering.

I. unguicularis likes the poor soils and dry conditions of the southern Mediterranean and North Africa, and flowers best when tucked up against a south-facing wall.

Planting depths

All irises, except bulbous varieties, should be planted with the broad, fleshy rhizomes at or just below the soil surface. The rhizomes need direct sunlight and mustn't be shaded by surrounding plants.

Plant bulbous irises 10cm to 20cm (4in to 8in) deep in autumn, and lift and divide as the leaves fade. Juno irises should be planted 5cm (2in) deep.

Feeding and dividing

Feed with a low-nitrogen, slow-release fertiliser and add extra lime for very acid soils. Late summer is the best time to move or divide most forms, but divide I. cristata just after its spring flowering.

When dividing the rhizome, keep the young, vigorous parts and discard the old. Water the newly planted sections in dry weather in their first season after transplanting, to help them establish new root systems.

Aftercare

Established clumps of some free-flowering irises can be rather untidy. This can be partially overcome by reducing the leaves to two-thirds their length in late autumn and gently pulling out any dead foliage.

This has the additional benefit of reducing the resident snail population that frequently causes unsightly holes in the flowers.

Growing from seed

Most iris species can be grown from seed, although some may take many years to flower. Hybrid irises won't grow true from seed and need to be propagated by division.

Pond irises are so vigorous they shouldn't be allowed to seed or they'll become a nuisance.

Take care when handling irises as the sap can cause skin irritation. All parts of the plant can be poisonous if eaten.

National Collections of irises:

Mrs Murphy
Myddelton House Gardens
Bulls Cross, Enfield
Middlesex EN2 9HG
Tel: 01992 702200
Website: (External) www.leevalleypark.org.uk

C Austin
Claire Austin Hardy Plants
Edgebolton, Shawbury
Shropshire SY4 4EL
Tel: 01939 251173
Website: (External) www.claireaustin-hardyplants.co.uk

JRL Carter
Rowden Gardens
Brentnor, Tavistock
Devon PL19 ONG
Tel: 01822 810275
Website: (External) www.rowdengardens.com

Head Gardener
Belsay Hall, Belsay
Newcastle upon Tyne
Northumberland NE20 ODX
Tel: 01661 881069

Mr M Pharoah
Marwood Hill Gardens
Marwood, Barnstaple
Devon EX31 4EB
Tel: 01271 342528
Website: (External) www.marwoodhillgarden.co.uk

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