VERNAL IRIS

I. cristata (crested iris); I. pumila (dwarf bearded iris); I. verna (vernal iris)

With hundreds of varieties to choose from, there are irises suitable for rock gardens of every kind and size. Some thrive in sun, others in shade. All are perennials, blooming in late spring or early summer. They grow from fleshy rhizomes and have sword-shaped foliage. The clear, vivid colors of iris blooms include pink, lilac, purple, white, cream, yellow, brown, maroon, orange, black and blue; the flowers of many varieties are bicolored.

The crested iris grows 4 to 9 inches tall and will spread to cover a large area, its rhizomes forming a mat over the surface of the ground. Its flowers are lavender, 2 to 2 1/2 inches across, with white crests marked with orange tips. The bright green broad, arching leaves die to the ground in the winter.

The dwarf bearded iris, suitable for a cool alpine greenhouse as well as a rock garden, is only 4 to 10 inches tall. It has blue-gray leaves and dark red-purple flowers. The vernal iris forms spreading clumps of shiny evergreen foliage, 3 to 10 inches tall. Because the flower stems are so short, the blooms seem to nestle among the foliage. The fragrant flowers, up to 3 inches across, may be purple or white.

HOW TO GROW:

The crested iris is hardy in Zones 3-8, the dwarf bearded iris in Zones 4-8, and the vernal iris in Zones 4-8. The crested and vernal irises do best in a moist, acid soil, pH 5.0 to 6.5, enriched with peat moss or compost. The dwarf bearded iris does best in a neutral soil, pH 7.0. All three species grow well in the high, open shade of deciduous trees, but the dwarf bearded iris is also recommended for full sun. Plant irises in the spring or fall, spacing smaller-growing species 6 to 9 inches apart, larger-growing species 12 to 18 inches apart. Prepare soil by digging a hole and mounding soil into it. Place the rhizome on top of the mound and spread out the thin, fibrous roots over the top. To prevent rotting, rhizomes of crested and dwarf bearded iris should only be half buried, with tips facing out from the center. Keep the soil moist around the rhizomes for several weeks. Irises are most often propagated by dividing the rhizomes, making sure each division has one, and preferably two, growth buds. They should be divided after flowering.