Iris (bulbous) iris
Height 10-67cm (4-27in)
Planting distance 5-20cm (2-8in)
Flowers early winter to; early to mid summer
Sheltered sunny site
Bulbs available early to mid autumn
The irises in this group all grow from bulbs, unlike bearded and beardless irises which are rhizomatous. The species bulbous irises, which flower in winter and spring, are the smallest and ideal for soil pockets in a rockery, the front of a border, or bare ground beneath deciduous shrubs. The hybrids, which appear in early and mid summer, make good cutas they are taller and larger flowered. Most bulbous irises are hardy and prefer light well-drained soil (ideally chalk or limestone), and a sheltered, sunny position.
Popular species and hybrids Iris bucharica has up to seven sweetly scented cream and yellow flowers on 45cm (18in) high stems. These appear in mid and late spring. It grows best in a light well-drained soil containing humus and some lime. An ideal position would be below deciduous shrubs or trees, which will shelter the plants and keep them dry in summer. Plant the bulbs 15cm (6in) apart in early autumn. Iris danfordiae has vivid lemon yellow flowers that appear in mid and late winter. The plants stand only 10cm (4in) high and the flowers have an attractive honeylike scent. Hardly any leaves are evident at flowering time. The bulbs should be planted 5-10cm (2-4in) apart in light well-drained chalky soil and in full sun. Iris histrioides ‘Major’ has bright royal blue flowers with a yellow central ridge on the falls. It is one of the earliest bulbous irises to appear, flowering in early to mid winter. The plant is extremely hardy, with blooms remaining un-scathed through the severest frosts and snow. At flowering time the leaves are only 2.5cm (1in) high, but by spring they may have reached 45cm (18in). As the flower stems are just 12.5cm (5in) high they look most effective grown as a mass in a rockery. It’s a useful species for the garden, being one of the few small bulbous irises to tolerate dappled shade. Set the bulbs 5-10cm (2-4in) apart in light, well-drained chalky or limy soil.
Iris reticulata has deep violet-blue flowers with a gold spot in the centre of each fall. The flowers appear in late winter and early spring and are accompanied by taller leaves. This species and its varieties are 15cm (6in) high and should be planted 5-10cm (2-4in) apart. ‘Joyce’ (sky blue), ‘Katharine Hodgkin’ (large, pale blue and yellow), ‘Natasha’ (white and blue, yellow markings), and ‘Pauline’ (violet, white and blue variegated blotches) are popular varieties.
Three types of hybrid bulbous irises have been developed, primarily from the xiphium species which are tender Mediterranean plants.
Dutch hybrids flower in early summer. Their colours range from white, yellow and blue to purple. The plants reach 38-60cm (15-24in) high. Set the bulbs 10-15cm (4-6in) apart in light fertile soil in a sunny site.
English hybrids are the last of the bulbous irises to flower, coming out in mid summer. They have the largest flowers, but the smallest colour range: whites, blues, pinks and purples that are often flecked. The plants reach 38-68cm (15-27in) high and should be set 15-20cm (6-8in) apart in rich soil. Spanish hybrids flower between the Dutch hybrids and English hybrids in early to mid summer. The fragrant blooms come in a good colour range, including smoky shades: whites, browns, blues, purples and mauves. The plants stand 30-45cm (12-18in) high. The bulbs should be set 15-20cm (6-8in) apart in light soil in a sunny position.
Plant the species and hybrid bulbs in early and mid autumn. Set species bulbs 5-7.5cm (2-3in) deep and hybrids 10-15cm (4-6in) deep. Feed species bulbs with a general liquid fertilizer once a month for three months. On heavy and wet soils, lift Dutch and Spanish hybrids after the leaves have died down and replant in early autumn. Protect them in winter with cloches.
After the foliage has died down, lift, divide and store the bulbs until planting time in autumn. The large bulbs will flower the following year, but small offsets may take two years.
Pests and diseases
Stored bulbs may be attacked by aphids and stem and bulb eelworms. Narcissus fly larvae can also be a problem. Leaves and stems, particularly those of I. unguicularis, may be eaten by slugs and snails. Rust occasionally occurs on rhizomatous irises. Blue mould may cause the bulbs of Spanish, English and Dutch hybrids to rot, andattacks the bulbs’ necks. Black spots appearing on the leaves during wet periods are a result of , a fatal fungus disease.