When you say the word "iris," most people visualize the exotic looking bearded iris, with the fuzzy ridge that resembles a caterpillar on its lower, downturned petals. The true story of the iris flower is that there are several varieties. All irises have similar spiked, fan-like foliage and three true petals (standards), and three petal-like sepals (falls). All types can be found in an array of colors, although their preferred growing conditions may differ, as does the blooming period.
Bearded irises can be distinguished by fuzzy little dabs of color on their falls. Bearded iris likes sandy to clay soils as long as they are well drained and not soggy. Bearded iris also prefers full sun in cool summer climates, or filtered afternoon sunlight or full shade where summers are hot and dry. Plant bearded iris rhizomes no more than 1 inch deep from summer to midautumn. Clumps should be dug and divided every three to four years to prevent overcrowding. There are four groups of bearded iris: tall; median; miniature dwarf; and aril and arilbred. Aril and arilbred irises are more temperamental than bearded irises and require alkaline soil with perfect drainage and hot, dry summers.
Japanese irises have 4- to 12-inch flat, single or double blooms, from late spring to early summer, with narrow upright foliage, each having a distinct midrib, and stems reaching a height of up to 4 feet. Japanese irises require rich, acid soil and large amounts of non-alkaline water, making them thrive in water gardens, although they will grow in well-watered garden beds. They require full sun in cool summer areas and high or dappled afternoon shade in hot summer regions. Rhizomes should be planted 2 inches deep in autumn or spring and crowded clumps should be divided in summer or early autumn.
Siberian irises have grass-like foliage and thin, reed-like stems, bearing two to five blooms with upright standards and flaring or drooping falls in midspring. They should be planted in spring or late summer in regions where winters are mild to moderate, with sun or light shade in neutral to acid soil. Rhizomes should be planted 1 to 1 1/2 inches deep. They do well in garden beds and prefer generous watering. Dig and divide when clumps reveal hallow centers, in late summer or early autumn.
Spuria irises have narrow, dark green, upright leaves with blooms that often have a prominent yellow spot on the falls. Rhizomes should be planted 1 inch deep in good soil with full sun. Spuria irises prefer regular watering, but do not like soggy feet. Divide in late summer or early autumn when they become overcrowded, which is indicated by a decline in performance.
Louisiana irises are native to swamps and moist lowlands in regions with fairly mild winters. Louisiana irises have long, linear, unribbed leaves with flattish blooms. They prefer rich soil and do well in shallow pond edges as well as well watered garden beds, with full sun in areas with cool, mild summers or light afternoon shade in intense heat. Rhizomes should be planted half to 1 inch deep, at least 2 feet apart to avoid overcrowding. Dig and divide clumps every three to four years in late summer.