How to grow iris

Types of iris to grow

Bulbous irises are lovely for bursts of seasonal colour, though their flowers last for a short time only, before they die back and return to dormancy. Popular bulbous irises include Iris danfordiae and Iris reticulata, which bloom as early as February, bearing exquisitely marked blooms on 10cm stems. Brightly coloured Dutch iris is sold as a cut flower and, when planted in gardens, blooms in summer, producing large flowers on tall, sturdy stems.

Border irises include bearded iris (Iris germanica) and Siberian iris (Iris sibirica). As their name suggests, they're ideal for growing in borders. Bearded iris is by far the largest group and is derived from species found in Mediterranean and Middle East regions, so thrives in dry conditions. Siberian iris grow well in any reasonable soil. Both types bear showy flowers on stout, upright stems. Bearded iris is so called for the caterpillar-like line of hairs on their lower petals. Several flowers are borne on each sturdy, branched stem above clumps of sword-shaped grey-green leaves. Bearded irises are sub-divided into groups: miniature dwarf, standard dwarf, intermediate, border, miniature tall and tall.

Moisture-loving iris are hardy perennials with colourful blooms in late spring and early summer, bearing flowers on tall, stout stems above clumps of sword-shaped leaves. They need soil that stays moist and doesn’t dry out at any time of year, but particularly in summer. These iris are best for growing in the margins of ponds, and bog gardens. The most popular species of moisture-loving iris are Iris ensata, Iris laevigata and the yellow flag iris, Iris pseudacorus.

When to plant irises

Plant iris bulbs (bulbous irises) in autumn, typically from September to November in the UK. Some bulbous irises (such as Iris reticulata) flower as early as February, so it's important to plant them in good time otherwise they will flower late. Don't worry too much if you plant your iris bulbs later than November, as long as the bulbs are firm and show no signs of mould they will still grow, they will just flower later than they're supposed to.

Plant border irises from late summer to autumn, or spring. Plant them so the top half of the fleshy root, or rhizome, is above ground and exposed to sun. Iris sibirica should be planted with the top of the rootball at ground level.

Plant moisture-loving irises in spring, summer, or autumn.

Where to grow irises

Bulb iris need full sun and must have well drained soil or the bulbs can rot. You can plant iris bulbs of dwarf iris such as Iris reticulata, in pots either outdoors or under protection in a greenhouse or a cool well-lit room. As with most bulbs, plant iris bulbs two to three times the depth of the bulbs itself. There's no need to soak them before planting. Grow larger bulb iris in borders.

Border irises need full sun and free-draining soil, as the thick root is a water-storing device. Iris sibirica can tolerate a bit more shade than Iris germanica.

Grow moisture-loving irises in permanently damp soil, bog gardens, or shallow water at pond edges.

How to care for irises

Allow leaves of bulbous irises to die back naturally so the bulb can build up energy for next year. Ensure iris bulbs don’t get too wet, particularly in winter, which can cause rotting.

Bearded iris are long-lived but flowering declines once clumps become older and congested. Rejuvenate them by dividing and replanting the younger, outer parts of the clump in late summer, discarding the older pieces of root.

Divide large clumps of moisture-loving iris in late summer.

Pests and diseases

Irises are affected by a number of disease caused by bacteria and fungi. Some affect the leaves while others affect the plant below the soil, including the bulbs and rhizomes. Leaf spot is most commonly found in bearded iris, and shows as small spots on the leaves with a brown or yellow margin. Remove infected leaves at the end of the season and burn them.

Ink disease typically affects bulbous iris, and appears as black blotches on the leaves. Plants affected by ink disease should be removed and destroyed (not in the compost), and avoid growing irises in the same spot for several years.

Rust affects both bulbous and rhizomatous irises. Removing affected leaves can slow down the spread of the disease, but take care not to remove all leaves as this can affect the growth of the iris.

10 Irises to grow

Border iris:

Iris ‘Edith Wolford’ is a bearded iris with bright yellow standards and violet, ruffled falls. It's perfect for growing in a mixed herbaceous border or gravel garden.

H x S: 90cm x 20cm

• Buy Iris 'Edith Wolford' from Thompson & Morgan

Iris ‘Feu Du Ciel’ bears orange-yellow standards and falls with a darker orange beard, in contrast with green-grey, sword-shaped leaves.

H x S: 80cm x 20cm

• Buy Iris 'Feu du Ciel' from irises.co.uk

Iris ‘Wonders Never Cease’ bears pretty flowers with white standard petals and white-edged bronze fall petals with a bright yellow beard, on slender stems.
H x S: 80cm x 45cm

• Buy Iris 'Wonders Never Cease' from J Parker's

Siberian flag iris, Iris sibirica, produces small, delicate flowers and narrow, bright green foliage. Flower petals are purple with white and yellow markings. Iris sibirica ‘Blue King’ bears deep violet flowers with veined yellow throats.

H x S: 1.2m x 80cm

• Buy Iris sibirica 'Blue King' from Burncoose

Bulbous iris:

Iris reticulata is an early flowering iris, bearing pale blue to deep violet blooms with central yellow splashes down the middle of each petal, from late winter to early spring.

H x S: 15cm x 10cm

• Buy Iris reticulata from Crocus

Iris reticulata ‘Katharine Hodgkin’ has larger flowers than most other dwarf irises. Each creamy white bloom is covered with distinctive blue veining.

H x S: 15cm x 10cm

• Buy Iris reticulata ‘Katharine Hodgkin’ from Crocus

Iris histrioides is a dwarf, bulbous iris bearing deep purple flowers with yellow markings, from late-winter. Perfect for winter pot displays.

H x S: 15cm x 10cm

• Buy Iris histrioides from Hayloft

Yellow flag iris, Iris pseudacorus, is a vigorous water iris, typically found growing at the edges of large, sunny ponds. It bears large clumps of green leaves from which elegant, yellow flowers appear in late-spring.

H x S: 1.2m x 1m

• Buy yellow flag iris from Crocus

Iris foetidissima is the perfect iris for a shady spot, particularly beneath trees, where other plants struggle. It has architectural evergreen foliage and dull purple flowers, but it comes into its own in autumn when its large seedpods split open to reveal rows of orange-red seeds that remain well into winter.

H x S: 75cm x 45cm

• Buy Iris foetidissima from Claire Austin

Japanese water iris, Iris ensata, has variegated foliage and rich purple flowers. Perfect for growing at the pond edge, it will gradually spread to form a large clump.

H x S: 75cm x 50cm

• Buy Iris ensata from Crocus