by William Rickatson Dykes (Author of “The Genus Iris,” Secretary The Royal Horticultural Society)
A Brief Study, by the Authority on Iris, of Resemblances and Differences Between Some of the Less Familiar Members of this Great Group
It is difficult perhaps for one who has always gardened in the island climate of the south of England, to foretell the behavior of the various Iris species when cultivated in America. But the fact that most species are natives of countries possessing a continental climate, with greater extremes of heat and cold than we usually experience in England, would seem to indicate that, on the whole, Irises should be easier to cultivate with success in the northern states than in England. In sheltered southern districts, however, where vegetation is practically unchecked throughout the winter months, there will probably be difficulties in the way of flowering certain species which in their natural conditions lie dormant for several months.
To many people the mention of an Iris suggests merely either a Bearded Iris, such as germanica, or else perhaps some form of Spanish Iris. There are, however, a number of others, very different from either of these types, which well deserve a place in our gardens and which will extend the flowering season of Irises far beyond the limits covered by these two types. Here in England, for instance, we can usually rely on getting numbers of blooms from the Algerian I. unguicularis or stylosa from October to March, except during periods of hard weather when the buds are killed by the frost. The lilac purple flowers are deliciously scented, and it is fascinating to pick a handful of buds and watch them unfold in the warm atmosphere of a room. This Iris belongs to the great section of Apogon or Beardless Irises. This Iris would seldom flower in the open I imagine, in the Eastern States at any rate; but on the other hand the small bulbous Irises, on which we rely for flowers during the first three months of the year, all come from Asiatic regions with cold winters. Actually these suffer here from the fact that a mild spell leads them to suppose that the winter is over and to put forth their flowers and their foliage, only to have the latter destroyed or damaged, and their bulbs correspondingly weakened, during ensuing winter weather. These early bulbous Irises belong to two sections: – the reticulatas, so called because their bulbs have netted outer coats; and the Junos, which are distinguished by the fact that the bulbs in their resting state have adhering to them a number of thick fleshy store-roots, which must be preserved intact if the plants are not to be weakened.
The wild Iris reticulata comes from the Caucasus and has red purple flowers with narrow four-sided leaves. It is sometimes grown, under the name of Krelagei, but seems not to have so strong a constitution as the commoner so-called “type” with brilliant dark blue flowers relieved by a central orange ridge on the blade of the falls. There is also a pale blue form called Cantab – from the colors of Cambridge University – and many other color forms are to be found among seedlings derived from these three, ranging down to a red-black.
In Northern Asia Minor there grows I. histrioides with large bright blue flowers, and further south the less brilliant but more variable I. histrio, of which I once received an extraordinarily dark red-black form. The delicate, gray-blue, almond-scented I. Vartani is from Palestine and in the hills of Northern Mesopotamia the brilliant little I. Bakeriana, whose flowers seem made of blue-black velvet, grows. As a contrast to these there is a single yellow-flowered species from Cilicia, I. Danfordiae.
The Juno Irises extend from the shores of the Western Mediterranean to the northwestern frontier of India, and contain among their number some excellent garden plants. The Spanish and Sicilian I. alata, I. palestina and the Asia Minor species of the pérsica group are all difficult to manage – chiefly, perhaps, because being natives of stiff clay soil the single seedling bulbs cannot put out offsets, and thus gradually extend and spread further and further. They have therefore developed into shortlived species which reproduce themselves freely by seeds. On the other hand, I. bucharica, native of Bokhara, with the growth of a miniature Maize plant and a white and yellow flower in the axil of each leaf, seems to revel in a sandy soil and increases fast by means of offsets.
Perhaps the most gorgeous of all is the Turkestan I. Rosenbachiana, which sends up its flowers as soon as the snow melts and before the leaves have time to develop to any extent. The flowers are sometimes white and a crimson purple, with a conspicuous golden crest; but others are of any shade of blue or red-purple while there are also rare examples of a pale straw-yellow. In England histrioides, Rosenbachiana, and Bakeriana begin to flower in January; then come the other reticulatas and the dwarf Junos allied to persica – stenophylla with flowers of two shades of blue-purple, and Tauri with red-purple flowers veined with gold. In March and April come bucharica and its allies: orchioides (yellow), Warleyensis (purple), sindjarensis (pale blue), and caucasica (pale yellow). In America the season would probably be shorter and all the species would begin to flower as soon as the snow melted.
These bulbous Irises are closely followed and indeed overtaken by the Dwarf Bearded Irises (Pogoniris) such as pumila, chamaeiris Reichenbachii, mellita, etc. All these species have many color forms, varying from yellow to purple, and all come from regions with cold winters, except chamaeiris which is from the south of France. There are two points to remember about their cultivation. One is that they must be grown in sunny positions, and the other is that, since they are shallow rooting plants, they should be lifted and replanted every two or three years as soon as the flowers have faded.
Of hybrid Pogoniris there are innumerable forms which it is not proposed to enumerate here, for we are concerned for the moment rather with the wild species from which our garden Irises have been evolved by selection and hybridization. The above mentioned I. chamaeiris has been used in conjunction with later and larger species to give us what are known as the Intermediate Irises – such as Ivorine, Dorothée and Queen Flavia – but there are wild species such as aphylla (purple white or pale yellow) from Central Europe, sulphurea (pale yellow) from the Caucasus, and Alberti (light blue-purple or yellow) from Turkestan which flower with these intermediates and of which the possibilities have been as yet only very slightly explored by hybridization.
There are at least half a dozen forms of I. germanica with apparently equal claims to be called the type – hence I. germanica is a puzzle! No one is undoubtedly wild anywhere, though the various forms have escaped from cultivation and established themselves widely – but always near habitations – from Spain to Nepal. Of each form there is also an albino, e. g., the well known florentina; and the truth would seem to be that all are of hybrid origin. Most are delicate in that their flower buds are liable to be killed by frost long before they have grown sufficiently to emerge from the leaves, therefore American gardeners in the North would probably be better advised to grow rather those hybrids which have sprung from the combination of the purple of I. pallida and the yellow and brown of I. variegata. The first known hybrids of these were called sambucina and squalens; and it was once my good fortune to go to a remote alpine valley 4000 feet above the Croatian coast of the Adriatic where, amid the melting snows in April, I dug up plants among which I found, when they flowered, both pallida and variegata and the hybrid forms.
For later flowering forms one of the best parents is I. trojana, which is reported to have come from the neighborhood of Troy and which is distinguished by its branching habit. Hybrids of it have given me stems bearing as many as fifteen flowers instead of the normal four or five of typical germánica. It is to I. trojana that we can trace such comparative new comers as Isoline and Alcazar. Pallida, variegata, and trojana are all well adapted to withstand a continental winter, and therefore are far better suited to American gardens than such magnificent plants as mesopotamica or Ricardi, which grow rapidly in any moist period in the autumn and then suffer in their foliage during the winter.
BESIDES the Pogoniris proper there are two other sections of which the flowers are bearded, though they are distinguished sharply by other characteristics. One is that of the Oncocyclus species, the most wonderful and the most difficult to grow of all Irises. I imagine these might prosper in the dry warm climate of parts of California and Arizona, but in the East the only hope apparently would be to keep them dry with the aid of a glass roof overhead, and thus to prevent their making any autumn growth above ground until the arrival of frost and snow insures their remaining dormant until spring.
The homes of these species are in Asia Minor, Syria, and Persia, and it is to be hoped that under a new and non-Turkish regime in these countries it will be possible to obtain specimens of them. They are characterized by their large flowers, delicately veined and dotted with the most amazing combinations of color in such beautiful species as Lortetii from Lebanon, or by the weird shape of the Persian paradoxa and the Caucasian acutiloba.
The other section comes from further east and is found centered in Turkestan. It is closely allied to the Oncocyclus section, but these Regelia Irises have two or three flowers instead of only one on each stem. The best known species are Korolkowi with conspicuously veined flowers, and stolonifera in which various shades of brown and electric blue strive for the mastery. These two sections have been hybridized together to form the Regelio-cyclus Irises, which to some extent combine the beauty and coloring of the Oncocyclus species with the vigor and greater ease of cultivation of the Regelias. Here 1 find it advisable to lift the latter in July and to replant them in October. Without this check they are apt in autumn to produce their foliage which is then damaged, if not destroyed, in winter. Probably with this treatment they would succeed admirably in the climate of New York.
Of the various groups of Apogon or Beardless Irises it will scarcely be possible to treat in detail here. To this section belong nearly all the native American species, many of which seem to be much more nearly related to European or Asiatic plants than to any other American members of the genus. Thus the common I. versicolor of the bogs of Massachusetts is practically only the purple counterpart of the yellow European I. pseudacorus. Forms of I. setosa are found on the coast of Maine, in Labrador, in the Yukon district and also in Siberia, while I. longipetala, from the coast near San Francisco, and two or three closely allied species growing further inland, are akin to the Asiatic I. ensata which flourishes from the desert regions of Central Asia to Northern China and Japan.
California contains a group of plants – I. Douglasiana, I. Watsoniana, I. tenax, I. Purdyi, I. bracteata, and I. macrosiphon – which, besides being beautiful in themselves have the further advantage that no two seedlings are precisely alike, while the range of color is extremely wide. The only drawbacks are that some of the species are none too vigorous in any climate less genial than that of California, and that the plants object to transplantation and must be established as seedlings in their permanent positions if they are to do well.
In the southeastern United States a curious distinct group is formed by the terra-cotta Iris fulva from the marshes along the Mississippi near New Orleans, the bold and vigorous I. hexagona from the same district and also from Florida, and its dwarf form from Arkansas, known as I. foliosa (syn. Hamancei) which, as it remains leafless during the winter, is probably the best suited to a more northerly climate. That this plant is closely allied to I. fulva was proved by the ease with which I was able to combine the two in a hybrid called fulvala. In this the blue-purple of foliosa has combined with the terra-cotta of fulva to form a rich dark purple practically unknown elsewhere among Irises. Moreover, the hybrid is more vigorous and easier to grow than either of its parents.
Another great division of the Apogon section centres round I. spuria, which is distinguished by the twin projecting ridges which run down each of the three angles of the ripe seed vessel. The flowers may be either blue or yellow, as in I. aurea, or white and yellow as in I. ochroleuca; and the tall stems and tall erect foliage make them an ornament to any border. To this group also belongs I. graminea, of which the flowers may have the fragrance of a ripe plum or green gage – though to obtain this a certain amount of selection may be necessary among seedlings, of which some are almost deficient in scent.
Last but not least comes the large group of sibiricas which flourish exceedingly in a cool, moist, vegetable soil – a group to which so many delightful discoveries in Western China have been added of recent years. Iris sibirica itself is a Central European and Russian plant with numerous slender, hollow stems which raise the rather small blue or white flowers well above the grassy foliage. In Eastern Asia this gives place to orientalis which has larger flowers on dwarfer and less numerous stems. A dwarf, yellow-flowered species is I. Forrestii while I. Wilsoni is taller but of a less clear yellow. The flowers of I. chrysographes are a rich dark velvety-purple set off with a patch of golden veining on the falls. This is one of the most striking of the new species.
All the members of this group hybridize together very easily and give a very wide range of results. I have also found it possible to combine the Himalayan representative, I. Clarkei as well as I. chrysographes with the Californian I. Douglasiana with a most pleasing result in the latter case. This hybrid has flowers of a pale crushed-strawberry pink, with a large patch of golden veining.
Intermediate between the Pogoniris and the Apogons comes the small group of Evansia Irises, represented in America by I. cristata and its close ally I. lacustris. In all the members of the group there is a linear crest, like a single cock’s-comb running along the centre of the blade of the falls. The finest species is probably I. tectorum (blue) with its beautiful white form. This Iris gets its name from the fact that it was found growing in lumps of clay on the ridge of thatched houses in China and Japan. It is probably a native of the provinces of Hupeh and Yunnan. Its Himalayan counterpart, I. Milesii, has smaller red-purple flowers and a much more vigorous growth. For some reason I have never succeeded in hybridizing these two species, although I have succeeded in combining the crest of tectorum with the beard of Pogoniris in the shape of a dwarf form of I. pallida. Two other Chinese Irises, japonica or fimbriata and Wattii, also belong to this group. The former will hardly ever flower in the open here, though the fact that it flourishes in Chitral, where extremes of temperature are at least as great as those in the States, seems to show that it has more chance of succeeding in America than I. Wattii, which alone of all I rises produces its flower stem in one summer but does not produce its flowers until the following spring.
Of the late flowering bulbous species, the well-known Spanish Irises (I. xiphium) is common in English gardens and welcome in America where it can be kept alive, but the knowledge may not be common that an early flowering race can be obtained by crossing flowers of the variety known to the trade growers as filifolia or praecox with pollen of any of the older varieties. (The true I. filifolia is a very different species and has flowers of the richest red-purple, a shade that is not found among forms of I. xiphium). Iris tingitana is the finest of all in this class but it comes from Tangiers and needs a warm climate to make it flower. And all these species do best in a warm, light, dry soil; consequently in gardens where the soil is cool and moist it is better to grow the so-called English Iris (I. xiphioides) which comes from the wet slopes of the Pyrenees. This Iris is called “English” because it first became known to botanists as growing in gardens near Bristol, to which it had been brought by early traders with Spain.
Perhaps enough has been said to show the variety and interest that can be found among the various species of Iris, though this is merely a rough scheme of the principal sections of the Iris genus. May I add that it is always of interest to me to hear how Irises flourish under conditions different from those which prevail in my garden here; and that, if I can help others to grow them, I am always ready to do my best?
Illustrations by the author.