Iris includes some of the loveliest of flowering plants. Their intricate blooms offer a rich spectrum of colors as well as textures ranging from silky satin to velvet. rises are among the easiest of perennials to grow, and they give an abundance of beauty with minimum care.
The iris has a thick fleshy root called a "rhizome" (pronounced rye-zome) about like a tough potato in texture. When you buy a new iris, you will probably receive a rhizome with clipped roots and leaves. It can remain out of the ground for a week or two without serious harm, but the sooner it is planted, the better.
New iris leaves appear in early spring, then about mid-spring a tall spike will emerge and then the flower unfolds.
Choose a sunny spot in well drained soil. Spade or turn over the soil with a garden fork to a depth of at least 10". Spread fertilizer and work it into the top of the soil. If possible, this should be done 2 — 3 weeks before you are ready to plant. A well prepared bed will result in better growth and more bloom. Don't starve your irises or make them compete with nearby grass or weeds for food and water. Many gardeners, iris and otherwise, have soil analyses made of their garden soil, then add the fertilizer of the kind and quantity the tests show the soil needs.
Soil should be light and loaming. If all you have is clay, add coarse sand and humus. Bone meal and a good garden fertilizer, low in nitrogen, are good for irises, but manure should be used only after it has aged for about a year. Otherwise, it may cause rot. Roots must be buried firmly to hold the plant in place, but the rhizome should be near the surface (very important for good blooms). An easy way to achieve this is to dig two trenches with a ridge between them, place the rhizome on the ridge and spread the roots carefully into the trenches. Be sure to firm the soil tightly and allow enough for settling to keep the rhizome above any possible standing water. Fill the trenches with soil, letting the top surface of the rhizome be just barely beneath the surface of the soil.
If you have several plants, plant them at least a 1-1/2' apart, "facing" the same way. The rhizomes will then increase in the same direction, without crowding each other too soon.
After 2 — 3 years, the rhizomes will begin crowding each other. At this point divide the plant, cutting the newer parts of the rhizome free from the old, which may then be discarded. Unlike the other bearded irises, arils need to be transplanted annually. Dividing iris' is best done between 1 — 2 months after the blooming season, usually in July or August.
Before you re-plant, you'll want to prepare the soil bed. Iris' aren't that fussy, but they do require good drainage. Till the ground to a depth about 4". Add pine soil conditioner or maybe a little peat moss, and a little compost. There's no magic formula for this mix of amendments. Mix these amendments into the soil, again to about the 4" depth.
When transplanting established tubers during the summer, there still should be leaf stems. You'll want to cut back these leaves to a height of about 4" — 5". Once the tubers have been removed from the soil, look for any diseased or damaged tubers, cut them out and discard. For multi-branched tubers, cut these into the different segments.
Plant the tubers in the prepared soil, spacing them about 1' apart. Arrange the tubers so they are all pointed in the same direction. They should be planted in the loosened soil to a depth of about 1". As this newly tilled soil settles down over the next few weeks, the tops of the tubers should be just at soil level which is their best growing position.
Once divided and replanted, the iris will put out new roots which help hold the plant firmly during the winter in areas where freezing and thawing can result in heaving the rhizome out of the ground. If you live in this type of climate, a mulching can be beneficial.
There are 2 basic types of iris: rhizomatous and bulbous. The rhizomatous irises have rhizomes as rootstocks. These are divided into several groups: bearded, crested and beardless. Bulbous irises grow from bulbs instead of a rhizome.
These irises are characterized by a beard along the centerline of the flowers petals. This group includes thousands of different cultivars and hybrids, most flowering in the spring and early summer. Bearded irises are easy to grow in fertile, well-drained soil in full sun. Some may tolerate partial shade and poorer soils.
Bearded irises are further classified into six groups based on bloom height and bloom time: miniature dwarf bearded, standard dwarf bearded, intermediate bearded, miniature tall bearded, border bearded and tall bearded. Within these groups are some that re-bloom in summer or fall. Iris species that re-bloom will generally benefit from additional fertilizer and water during the summer.
These have ridges or cockscomb-like crests instead of beards. Many of these are found in damp woodlands and in the landscape they will benefit from a sheltered position in organic soil.
This group of iris obviously doesn't have a beard. They do have similar cultural requirements to the bearded, but some prefer a heavier soil.
Culture of the beardless irises is a little different than from that of the bearded irises. Transplanting should be done in the fall or in early spring. Exposed roots should never be allowed to dry out while out of the ground. Water heavily after transplanting. They should be set slightly deeper than the tall bearded. Japanese iris should be planted in a distinct depression in heavy soil to assist in supplying moisture to the plant. Siberians and the Pacific Coast Natives can tolerate light shade but the Spurias, Japanese and Louisianas demand full sun. Louisianas and Japanese require moist conditions during the summer months while the Pacific Coast Natives enjoy a very low humidity and dry soil no matter how hot it may get. All, except Louisianas, should be planted in a permanent spot where they can remain for many years as they resent being disturbed. Louisianas tend to creep; and therefore, should be tended to every few years. All are heavy feeders and need to be fertilized regularly.
There are are 3 types of bulbous irises: reticulata irises, juno irises, and xiphium irises.
These are a dwarf, hardy bulbs that flower in early spring. They prefer a sunny position in well-drained acidic or alkaline soil.
This group is a difficult iris to grow. They require a fertile, well drained soil and full sun with a dry dormant period after flowering.
This group includes the brightly colored Dutch, English and Spanish irises. They are often grown as cutting flowers. Any well-drained soil in full sun is suitable. In extremely cold climates, remove the bulbs to over winter in a frost-free location and then replant in the spring.