The irises most often used as garden plants fall into three main groups: Bearded Irises, Aril Irises and Beardless Irises. Each group has its unique qualities, and a collection including representatives from each group will be varied indeed. For cultural information on the irises described below
Bearded Iris are identified by thick, bushy “beards” on each of the falls (lower petals) of the blossoms. Originally, most of these were native to central and southern Europe. The American Iris Society has divided the bearded irises into six groups for garden judging awards.
1. Miniature Dwarf Bearded (MDB) — the tiniest of bearded irises, with height of up to 20 cm (8 inches). They are also the earliest to bloom. They are most effective in rock gardens or planted in drifts where they make a “carpet of color.”
2. Standard Dwarf Bearded (SDB) — some of the most useful garden plants, ranging in height from 20 cm (8 inches) to 41 cm (16 inches). They begin their bloom as the MDBs are ending, still quite early in the iris season. They are best displayed in clumps where they give the effect of a “cushion” of individual blooms. The colors are nearly unlimited since the SDBs show all the different “spot patterns” of the miniatures, as well as the plicatas and pinks seen in the TBs.
3. Intermediate Bearded (IB) — stand from 41 cm (16 inches) to 70 cm (27 1/2 inches) high, with their bloom season overlapping the SBDs and the TBs. Although the IBs show their dwarf ancestry in early bloom season and very interesting color patterns, they are large enough that their individual stalks may be nicely branched, forming an elegant bouquet. Some varieties are nicest in clumps, where they present a large amount of color (like the SDBs), while others are showiest in specimen plantings, where the stalks and individual blooms may be seen to best advantage.
4. Border Bearded (BB) — essentially small versions of the TBs in the same height range and bloom size as the intermediates, but blooming with the tall beardeds. Good BBs have round, ruffled petals that complement their small size.
5. Miniature Tall Bearded (MTB) — this class is distinguished by daintiness and delicacy. Height from 41 cm (16 inches) to 70 cm (27 1/2 inches). The blooms are smaller than on a BB and the stems are thin and wiry. An MTB clump looks like a cloud of butterflies. They are often called “Table Irises” because they are so well suited for arrangements.
6. Tall Bearded (TB) — have stalks with a height of 70 cm (27 1/2 inches) and above, with branching and many buds. Each stalk, in itself, makes a stately arrangement in the garden or in a vase. In addition to a wide variety of colors and patterns, the TBs display other qualities (such as ruffling and lacing) more frequently than do the other classes
Even if you grow nothing but bearded irises, you can enjoy a remarkable range of color and a bloom season extending for months. Some bearded irises are “rebloomers”, blooming again in the summer, fall or winter. Additional water and fertilizer applied during the summer months encourages them to bloom again. There are now reliable attractive rebloomers available which will perform in all but the coldest climates.
Incidentally, the word “median” refers to all the bearded irises except the miniature dwarfs and the tall beardeds; that is to say the SDBs, IBs, BBs and the MTBs. Strictly speaking, the word “dwarf” means only the MDBs.
Two very different types of irises are grouped together under the term “aril”. These are the oncocyclus and regelia irises of the Near East. Although they have beards, they are not classified with the bearded irises because they are so different. Actually, their beards are rather sparse, being long and straggly on the regelias, and nothing more than a wide “fuzzy” patch on the oncocyclus. The arils show dark signal spots below the beards with much veining and speckling, in an unbelievable range of colors. Unfortunately, the arils are difficult to grow in all but the warmest and driest regions of the United States.
However, in this century, hybrids were produced from crossing the arils with the more common bearded irises. These are called “arilbreds” (AB), and are usually very easy to grow and still display the spectacular features of the arils. Most arilbreds are tall and have large blooms. They usually bloom earlier than the TBs, with the SDBs and the IBs.
There are also small arilbreds, produced from crossing arils or arilbreds with dwarfs or medians. They are variously called “arilbred-medians”, “aril-medians” or “aril-meds”.
Beardless Irises are mostly native to Asia. The first four types are commonly grown in gardens, and they all bloom after the TBs, extending the iris season even longer. The fifth type, the Pacific Coast Native, blooms before the TBs and is native to the western regions of the United States.
1. Spurias (SPU) are tall (2 to 5 feet in height) and elegant, and have very attractive foliage. The shape of the bloom often suggests orchids and the colors range from white and yellow through blue, wine and brown, often with bright yellow signals.
2. Siberians (SIB) perform best with cooler conditions, regular moisture and a slightly acid soil. The blooms can be blue, purple, red-violet or yellow with newer cultivars in brown and orange shades, and can have a variety of forms from upright to flat and round. They are most attractive in established clumps that develop a bouquet effect and grow to a height of 2 to 4 feet., although some dwarf varieties are also available. Their grass-like foliage after bloom is one of their attractive garden features. They tend to bloom slightly later than the TBs.
3. Japanese (JI) require a slightly acid soil and present some of the most spectacular flowers of all the irises. Blooms are usually huge, ruffled and flat in form; some are marbled with gray or white. They bloom about a month after the TBs. Japanese hybridizers have worked with them for over 500 years.
4. Louisianas (LA) are native to the American Gulf Coast; they require soil that is somewhat acid and wet in the spring. The blooms are usually very wide petaled and open, showing brightly colored style-arms and sharp signal-crests.
5. Pacific Coast Natives (PCN), or Californicae (CA), are not widely grown as they are intolerant of the climatic conditions of all but the far western area of the country. Where they can become established, they grow most attractively with graceful and dainty flowers held one to two feet high, in most colors and patterns.
6. Species often enhance gardens with their delicate beauty. I. confusa (Evansia) requires conditions similar to azaleas in a frost free climate. I. missouriensis enjoys wet springs and dry summers.