Siberian Irises

The beauty and grace of Siberian irises add a special dimension to any garden bed or border. When they are in bloom, the delicate-looking flowers float like butterflies above the slim sword like leaves. When they are not in bloom, the foliage adds a handsome linear quality to the texture of the garden.

Siberian irises are one of the best known and best loved of the beardless irises. The slender leaves of Siberian irises are a design asset in themselves, but when topped by branched stalks, each bearing up to nine or more flowers, the effect is sensational.

History

Iris sibirica and I. sanguinea, the two species that botanists accept as major species of the Siberian series of beardless irises, undoubtedly have been cultivated for over two centuries. I. sibirica, a plant of wet meadows from central Europe and northern Italy all the way to the land west of Lake Baikal in Russia, is a handsome iris that undoubtedly appeared in early gardens. The violet-blue to blue flowers usually have darker veins and have been bred into cultivars that range from purest white to deep violet blue.

I. sibirica was first recorded and named by Linnaeus in 1754. Today, a number of species are included within the series Sibiricae, of the section Limniris, which is part of the beardless iris subgenus Limniris. I. sanguinea, originally named I. orientalis, was next discovered and described by Thunberg in 1794. This iris originally grew from the land east of Lake Baikal all the way to Japan. The majority of Siberian iris cultivars derive from these two species, I. sibirica and I. sanguinea.

In addition to these two species, botanists recognize eight other species in the series Sibiricae, all from central and eastern Asia. These were discovered and named between 1875 and 1933. The plants of all ten species of this series are quite tall and thrive in the damp soil of mountain meadows and thin woodlands.

Characteristics

The foliage of Siberian irises ranges from rich green to glaucous blue green with leaves that are narrow and erect. The foliage rises above slender rhizomes. Each tall clump makes a statement in the garden landscape, providing a focal point that enhances the bed or border. While flower size and the height of the flower stalks should be in proportion to each other, the tall stalks of Siberian irises may carry small flowers gracefully on slender stalks that sway over the foliage.

Well-branched stalks are an asset so long as the stalks and flowers are well spaced and don't interfere with one another. Typically, there will be a stalk plus two major branches so that flowers are borne on three different levels. Bracts should be in proportion to the stalks, neither too wide nor too long, and should remain colored and healthy after the blooming season is past. Breeders and growers alike give high points to a long sequence of bud bloom, as that can appreciably lengthen the blooming season.

The graceful flowers must be in proportion to the plant. Ruffled flowers are often pleasing in contrast to the more normal yet handsome tailored types. The falls of Siberian irises influence the beauty of the flowers, varying from narrow to round and from vertical to horizontal. Although narrow strappy falls are undesirable, those with rounded or oval shapes that arch downward are as desirable as the more flaring types.

The flower standards vary widely in size, shape and position, with some being inconspicuous while others are relatively large and even arched or domed. The overall effect and grace of the flower are what counts. The falls may have unusual texture-silky, shiny, rough, metallic or velvety. Texture is a surface quality primarily of the falls that influences the impact of color by reflecting or absorbing light. Siberian iris flowers should remain fresh for several days.

Colors range from nearly black and wine reds to purples, lavenders and blues, to pinks, whites and yellows. The colors of the flowers should be clean and clear and should not change significantly until aging of the flowers is advanced.

Culture

Most gardeners find these irises both reliable and easy to grow. In general, the beardless irises require more water and an acid soil. This is in contrast to the general cultural requirements for bearded irises that thrive with less water and in a more nearly neutral soil. They are easy to grow just about anywhere, although they will bloom less, if at all, in shady sites.

New roots begin to grow shortly after blooming and that seems to be a good time to divide Siberian irises. Therefore, you can successfully divide and plant these irises after the blooming season in July or August when they will have ample time to grow new roots and re-anchor themselves to the soil before cold weather.

Many gardeners have success with planting Siberians in the early fall. In the early spring, when the plants are under 3 to 4 inches tall, is another time when it is easy to divide and move Siberian irises. Whatever timing you choose, be sure they have time for the rhizomes to begin growing new roots before the rigors of winter or summer. Plant the rhizomes horizontally with the foliage side up so that the tops of the rhizomes are 2 to 3 inches below the soil surface.

Once established, they will readily naturalize in the landscape, providing blooms year after year as reliably as naturalized daffodils. The single qualification is that they have an acid soil and, for most of the garden cultivars, ample moisture, although once they are established, they can tolerate droughty periods fairly well. Though even moisture is needed, good drainage is also appreciated. Plan to incorporate plenty of humus, sphagnum peat moss, compost, well-rotted manure or other organic material into the soil. Although many growers recommend keeping the soil at a pH of about 5.8, others report that the pH is not all that important. One thing is for sure, plants grown in a highly organic soil are more tolerant of a wide range of environmental factors, including pH, than are plants grown in a more mineral soil.

While highly organic soil and consistent moisture head the catechism for growers of Siberian irises, there always will be those exceptions that may well thrive in or at least tolerate alkalinity and a heavy clay soil.

When Siberian iris clumps outgrow their allotted space or when you want to divide them in order to spread them around, choose a cool, invigorating day to work. When making divisions for replanting, be sure that each division has about a half dozen or more fans of foliage and protect the roots from drying out during the replanting process. Make the new planting holes large enough to spread the roots, then tamp the soil gently into the hole and water the newly planted irises thoroughly.

Species

I. sibirica

This iris grows naturally across Europe from western France and Switzerland, through Russia, the former Yugoslavia, Bulgaria, northern Turkey and the Caucasus. Dormant in winter, the grassy, graceful foliage appears in spring; typically the flower is blue-violet, attractively highlighted at the base (haft) of the falls with a white mark, veined in the main color. The flower stems are taller than the leaves -often reaching over 32 in (80 cm) -ensuring visibility. This is the archetypal "butterfly" Siberian, its flowers are delicate, slender in profile, with pendent falls and stiff upright standards.

I. sanguinea

Native to Siberia, China, Korea and Japan, is similar to I. sibirica, but the flower spike is shorter and carries no branches. The flowers, though larger than those of I. sibirica, do not appear above the foliage and are darker in color -a deeper red-purple with heavier veining on the haft of the fall.

I. chrysographes

This iris is quite simply stunning. Slender, refined, understated, it is a native of China, Burma and Tibet and was collected by Ernest Wilson in Sichuan in 1908. The flowers are a rich purple with fine gold markings resembling an ancient script, hence its name. The flowers, delightfully fragrant, appear in late spring or early summer. There is a form, var rubella, with flowers of a reddish wine, and a black form.

I. clarkei

Another species from the roof of the world -Nepal, Tibet, India and Burma -was brought to the West after being collected in 1875 near Darjeeling, by Charles Baron Clarke. Untypically, it has solid stems. Flowers, with pendent falls and almost horizontal standards, range in color from violet through blue, appearing on up to three branches in early summer. Its foliage is wide and glossy.
In some areas in the eastern Himalayas it is said to be so plentiful and widespread that it is cut and dried for fodder for horses and yaks.

I. delavayi

A native of China, was brought to the West in the 1890s by a French missionary, L'Abbe de la Vaye, who discovered it in 1884, growing in swamps in Sichuan. It is one of the tallest species in the group, growing to 5 ft (150 cm), and has the widest foliage. The spike is well branched, with six or seven dark violet blooms, each bearing white veins and a signal patch. The falls are pendent and the standards are almost horizontal.
A swamp-dweller, it makes an ideal bog garden plant, flowering in early to mid-summer. It is easy to raise from seed but needs to be hand-pollinated as it has promiscuous habits.

I. wilsonii

Grows to about 30 in (75 cm), has gray-green leaves and the rather large, pale yellow flower is decorated with violet veining on the falls. It is more robust than I. forrestii, flowers later in the summer and its leaves are as tall as the flower stems.

I. forrestii

Is much shorter, attaining 14-16 in (35-40 cm) in height. The leaves are shiny on one side, dull on the other and much shorter than the flower stems.
Its color is a clearer yellow than I. wilsonii, with narrower falls faintly veined. Initially the standards are erect but they soon curl outwards. Less vigorous than the other Sino-Siberians, it is important to water during late summer to prevent it drying out.

I. bulleyana

This iris comes from China and in the past there have been doubts about its heritage, with some thought that it may be a hybrid of I. chrysographes - and I. forrestii. However, with increasing numbers of plant seekers exploring in China, new finds indicate that it is a species in its own right but with variable forms.
It is compact, reaching about 16 in (40 cm) in height and, in the best-known form, the standards and the tips of the slightly rounded falls are dark indigo blue, while the center is white with deep blue spots and veins.

I. dykesii

It is perhaps another hybrid and is like a vigorous form of I. chrysographes, with bright, deep violet flowers that have white and yellow fall markings. It is not known in the wild and is rare in cultivation.

I. typhifolia

A sibling of I. chrysographes, has recently become available for cultivation. It's a slender, elegant plant with very tall, twisty, thin foliage and its dark blue flowers with long pendent falls encourage growers to keep persevering even in the face of its reluctance to flower every season.

I. phragmitetorum

This iris was once collected in the Yunnan province of China but is unknown in cultivation.