A cheat's guide to bulbous irises and top tips for growing them

In the swelter of last summer, a coolly white iris called ‘Immortality’ bloomed until the end of October. This was a rhizomatous, bearded or ‘Germanica’-type iris, a group of sunseekers providing generous dobs of colour from the iridescence of the rainbow to smudgy embers.

The Sibericas are more shade-accepting, less gaudy and a tiny bit uptight in form. Both groups flower in summer, but have useful sword-shaped leaves throughout the year that offer, in painterly terms, a vertical thrusting mark against sleepy mounds of perennials.

In theory, irises can be picked from November (Algerian and Lazistan iris) until late summer. Where I get muddled is with bulbous irises, which flower from now until midsummer.

Bulbous irises come in three groups, of which Iris reticulata is the most familiar. These bulbs wear a netted tunic or reticule — like a string bag around the bulbous larder that sustains them in the gasping summers of Asia Minor. Their enamelled blooms, a hand in height, consort with solitary bees in spring.

All iris flowers employ a miraculous symmetry, formed in threes — standards, falls and the strap petals — to seduce pollinators and gardeners. ‘Harmony’ and ‘Cantab’ are mostly blue, but ‘Clairette’ and ‘Blue Note’ have dazzling indigo falls, flaked white. ‘Katharine Hodgkin’ — azure dashes on lemon, like Monet’s kitchen — is the most reliable for spangling through dead winter beds. Mr B thinks their strangeness is best appreciated grown on the kitchen table.

The second group — similar, but more rarified — is the Juno species, whose heartland is Afghanistan. Flowering in April, they like a loamy, neutral, well-drained situation. The most straightforward of these to grow seems to be Iris bucharica, a glistening, white triangulated flower with striking yellow falls on a knee-high stem. Twice as tall, but less outstanding are the pale-blue flowers of I. magnifica. They form good-sized clumps, according to bulb guru Christine Skelmersdale.

The third group of bulbous irises is confusingly named English, Spanish and Dutch. The latter were bred, by the Dutch, from the soi-disant English and the genuinely Spanish Iris xiphioides in the 20th century. The first Dutch, a cultivar named ‘Wedgwood’, was followed by blends of bronze, cinnamon, yellow, azure and milky white — less Staffordshire, more polychrome Delft. Manipulated to flower all year round, they became the florist’s iris, familiar on the garage forecourt, which makes them feel slightly unethical for today’s gardeners.

However, as garden flowers, they can be encouraged to return perennially. We experiment with Dutch iris and tulips in plastic pots sunk into large terracotta pots, which are lifted for drying. Try them in raised beds as you would asparagus, at a finger’s depth, or at the base of a sunny wall.

The rhapsody of bohemian named varieties — ‘Picasso’, ‘Gypsy Beauty’, ‘Paris Violet’ and ‘Tiger Mix’ — take up little room, their grassy foliage disappearing as with daffodils. Loving their dabs of pure pigment, Monet grew irises at Giverny in France, in thin beds, never over-shadowed, but with columbines, tulips and forget-me-nots.

Our only native English irises are the water-side ‘flag’ (Iris pseudacorus) and the Gladwyn (I. foetidissima). The bulbous so-called ‘English’ irises — I. latifolia (I. xiphioides), I. anglica and I. xiphium — are not remotely from these isles, but from the Pyrenees. Baffling, but they were first named botanically when ‘discovered’ near the Bristol gorge in the late 16th century. Much later, botanists concluded they were Spanish, brought perhaps by Spanish sailors, young muleteers from the ‘high peaks hoar’, as Hilaire Belloc wrote of the Pyrenees in his poem Tarantella.

Sturdy leaves push up before the snow melts and, in July, their tall flowers embroider the dusty meadow grass, a reminder that nature does perennials-with-grass with such élan. They will naturalise here, given a moist neutral soil, but are difficult to find. Anna Pavord says in Bulb that by 1808 there were 47 varieties listed by one Haarlem nursery, but only six were in the RHS Plant Finder. We planted them in the orchard at Trematon in Cornwall — ‘King of the Blues’ and ‘Mont Blanc’, from Parker’s Dutch bulbs. We wish to do the same here, but cannot find them.

Parker’s offers instead a ‘modern selection’ (‘King Mauve’, ‘Mickey Gold’, ‘Miss Saigon’), which they say ‘surpasses’ the old with better blooms and hardy longevity. It cannot confirm until July whether ‘King of the Blues’ and ‘Mont Blanc’, will feature in the autumn catalogue.

Here’s hoping that, if they do, every one of you will ring and ask for them.

Isabel Bannerman is, with her husband Julian, a leading garden designer.