Bulbous Irises

The irises in this division grow from bulbs similar in make-up to the vegetable that causes so much grief when it's peeled. Whether we are aware of it or not, some of the best-known irises -those most often seen in florists' shops -grow from bulbs, the Dutch, English and Spanish irises, tall aristocrats with shapely, rich-colored, purple-blue and yellow flowers.

All the bulbous irises lose their leaves after flowering, all are summer dormant and need to be lifted from time to time, and all the species can be raised from seed, though the wait for the first flower will be longer than with seed-raised plants of the rhizome-forming groups. Increase of hybrids true to form can come only from bulblets that form each season from the parent bulb and of course species also increase this way.

As with daffodils, the foliage of these irises starts to look untidy once flowering is over for the season. When the leaves start to flop around, tidy gardeners have that urge to grab the secateurs and cut them off. But do not do it. The bulb is pregnant. It needs cherishing and the leaves help to nourish it. The last month or two of growth is vitally important, for this is when the buds for the following season are forming.

Bulbous irises do not like heavy clay but adding sand, gravel and humus can turn this kind of soil into a hospitable home. When storing the bulbs out of the ground, make sure their resting place is shaded, cool and dry, and that air circulation is good.

Xiphium -Dutch, English and Spanish irises

When you buy irises as cut flowers you will most likely buy Dutch, English or Spanish irises. But the names are confusing. The ones we buy and grow are mostly hybrids bred from an original group of about eight species, all from western Europe and north Africa. The English irises are hybrids derived from I. latifolia, a native of the Pyrenees; Spanish irises are descended from I. xiphium, which originated in countries bordering the Mediterranean, including Spain; the Dutch irises were developed early last century by Dutch growers seeking to extend the flowering season of the Spanish iris by crossing it with I. xiphium species and I. tingitana from Morocco. The Dutch hybrids produce bigger, earlier-blooming flowers than the true Spanish irises. Now their cultivation is so controlled that flowers can be produced at any time of the year.

Each bulb most commonly bears one flowering stem which produces two blooms that open in  succession. Dutch irises flower in spring, before the tall bearded irises but at the same time as many of the Spanish irises. Both should be lifted at least every two or three years, just when the foliage is drying off, and left to dry in a shady place. But they must be replanted in time for the new roots to grow - about August in the northern hemisphere, February in the southern hemisphere. Left out of the ground until fall, the bulbs will lose vitality, be more susceptible to disease, and their flowers will be of poorer quality.

They like good drainage, moderately rich, well worked soil in a sunny location, and a light topdressing of lime. Poor soil makes small flowers; too rich a soil may encourage fungal disease. Plant the bulbs about 4 in (10 cm) deep.

Xiphium hybrids are tall plants, some growing to 3 ft (1 m) or more in height. The only way for them to reproduce true to form is from the bulblets that grow on the parent bulb each season once flowering is finished. If the main bulb is lifted every year and the babies detached, it is possible to build stock quickly. Lift the bulb in early summer and allow it about a month to dry thoroughly before detaching the small bulblets. Put these back in the earth as quickly as possible before there is a chance for mold to attack them. Soil rich in humus will encourage them to continue growing until late in the season.

Spanish 'Delft's Blue', a dark purple-blue hybrid, the paler blue 'Enchantress', the pale blue, early flowering Dutch 'Wedgwood' and the darker blue 'Professor Blaauw' are rewarding plants for the garden and they make excellent cut flowers. When cutting blooms, always leave at least four leaves to nourish the bulb and take care not to damage it with the knife or secateurs.

Xiphium irises are prone to virus attack. This shows as yellow streaking in the leaves which then rot at the base. Infected bulbs need to be dug out and burned. Fumigate the ground before replanting with any bulbs.

Species

I. xiphium

Giving its name to the group, has several flower color forms in the wild -two-toned blues, yellows and combinations of whites, yellows and blues. The signal, whether a stripe or patch, is gold or yellow and is often quite prominent. The foliage, which appears in the fall, is glaucous and initially fine, gradually broadening as it matures.

I. tingitana

This iris is a stunning plant. The tall, silvery, broad foliage is lovely in winter and the flowers are gorgeous, not because of any flamboyance but for their classic style that never loses its appeal. The standards are lavender blue, long and upright, tapering to a point. The falls are pendent, very blue on the wavy margins but shading out to palest lavender on the blades with clear yellow signals. Growing to over 3 ft (1 m), it bears only one flowering spike.
Plant the bulb about 1 1/2 in (5 cm) deep with sand above and below. This iris likes a loose soil rich in humus, good drainage, a hot sunny position and protection from frost. It appreciates lime and a top-dressing of potash in the growing season, during winter and early spring. In climates with summer rain it should be lifted after the foliage has died down and replanted in early fall.

I. juncea

This iris is notable for its vivid orange-yellow blooms, the second one in the sheath rising above the first on a long pedicel tube. They come into bloom at the same time as the tall bearded irises. A more slender plant than the Dutch hybrids, it grows to about 12 in (30 cm) with the flowers produced on 30 in (75 cm) stems. The bulbs differ from other bulbous irises with a hard, dark brown skin that splits into long fibers at the neck. Usually this plant increases by producing two large bulbs from the base but it can be grown from seed in sandy soil.

I. latifolia (syn. I. xiphioides)

This iris is the latest-flowering of the Xiphium group, coming into bloom in early summer at the same time as Japanese irises. A native of damp meadows in the Pyrenees, it is used to snow in winter, and thawing snow and rain in spring and fall, so it does hot need to dry out in summer, though it never likes to be waterlogged. These irises also tolerate lightly filtered shade.
Foliage, similar to that of Juno irises, first appears in spring. The flowers, ranging in color through all the purple-lavender-blue shades to white, are borne on 12 in (30 cm) stems. These irises are better left undisturbed for three or four years; when finally lifted after the foliage has died down, the separate bulbs should be replanted immediately, as each develops an important root system during summer and fall.