Thefamily is exceedingly large but, fortunately for the average gardener, the genus has been formed into several divisions which makes it easier to decide the particular culture any one section or even variety needs.
In the case of the bulbous irises, it is possible to grow varieties varying in height from a few inches up to 3 ft or so. Some of these if planted in August and September will produce their first blooms in February, to be followed by other varieties, which will prolong the flowering period until June. Bulbous irises can be classed into three divisions.
The first is the reticulata group, consisting of varieties which are dwarf growing and very early blooming.reticulata itself has dark-green pointed foliage and 8- or 9-in. Stems which carry violet-scented with an attractive orange ridge on the falls. It establishes itself easily and if left provides a delightful year after year. It has several good forms, including Tantab’, pale blue standards with darker falls and a golden crest; `Cyanea’, dark blue; ‘Royal Blue’ is sweet-scented; ‘Hercules’, bronze-violet; while `Wentworth’ and `Joyce’ are purple-blue. ‘R. Krelageii’ is bronze-violet but lacks scent; and ‘T. S. Dijt’ is a reddish-purple. All of these should be given an open, sunny sheltered from strong winds. Good is essential.
Iris histrioides major is blue with dainty yellow markings; ‘Bakeriana’ is rich blue, flowering in late January, while the golden-yellow Iris danfordiae blooms on 3-in. Stems in February. After flowering, the bulbs of this species split up into bulblets, which need looking after for two or more years before they bloom.
Quite different from the other types of bulbous irises, the second section, Juno, includes species with wide foliage and thickishfrom which the flowers appear in the axils of the . They like a sunny , a fairly rich soil and normally increase well if left undisturbed. One of the best of this type is `Bucharica’, 12-15 in. high, with glistening white flowers having clear yellow falls. Similar in habit, `Graeberiana’ is a lovely cobalt-blue, but perhaps the prettiest of all is Iris data or the `Scorpion’ Iris, producing during the winter scented, lavender-blue flowers. Growing 6 in. high, it should be given a sheltered place outdoors and is first class for pot culture.
The third class of bulbous irises is that known as the Xiphium and Xiphioides section, consisting of the so-called Dutch, Spanish and English varieties. The Dutch sorts bloom during May, a fortnight before the Spanish, and are stronger in growth and of better substance than the latter. Ideal in the border, some are excellent for forcing, especially Imperator’, lavender-purple with orange blotch, and ‘Wedgwood’, blue. In the Spanish irises are found many interesting colour blendings.
The foliage of the English irises is considerably broader than that of the others, while the bulbs are larger with looser skins. Growing 18-24 in. high, they continue to flower well into July. The bulbs of the Dutch, Spanish and English sorts should be covered with 3 in. of soil, but whereas the first two like a sunny and well-drained soil, the English varieties prefer a moist, although not waterlogged, situation.