Irises

Don Nicholson


Iris is the Greek word for rainbow and no word would more aptly fit this perennial which is not only one of the easiest to grow but also give an abundance of beauty, colours galore, with a minimum of care. The iris has a thick fleshy root called a rhizome more or less like a tough potato in texture; the exception is the Dutch iris which is a small bulb planted in the fall for spring bloom.

When classified, the iris are bearded or non-bearded, the beard referring to the fuzz on the upper surface of the lower hanging petals or "falls". The bearded range in height from the Standard Dwarf Bearded at 8 inches to 15 inches which are the earliest to bloom to the Tall Bearded that are over 27 inches blooming a month later (there are even a few of the Tall that are rebloomers in late summer). The beardless iris group includes those with smooth falls and leaves which are long (2í-4í) and relatively narrow; Japanese and Siberian Iris are part of this category.

Iris in our area are best planted in July, August or at the very latest, early September. It is imperative that the roots of newly planted Iris be well-established before the growing season ends.

Bearded Iris need at least a half day of sun and should be provided with good drainage, planting either on a slope or in a raised bed. If your soil is heavy, course sand or humus (compost) may be added to improve drainage. Proper depth when planting iris is critical. I make a little mound for each iris so that only the tops of the rhizomes are exposed and the roots are spread out facing downward in the soil. Firm the soil around each rhizome and then water to help settle the soil. Many people plant the Iris too deeply. I like to plant Iris 18 to 24 inches apart. Close planting will give an immediate effect but will require thinning often.

Overwatering is a common error. Newly planted iris need moisture to help get their root systems established, but once established donít need to be watered unless it is a dry summer or drought.

In about 3 years, the new rhizomes will begin to crowd each other and you will want to divide the plant, cutting newer parts of the rhizomes away from the old, which may then be discarded. The original rhizome may produce three more rhizomes in the first year if it is healthy and each of those rhizomes in turn may produce three more rhizomes the next year and so on. Dividing is best done one to two months after blooming, usually July or August. Soon after this time the Irises grow roots which help to hold the plant firmly during winter in areas where freezing and thawing can result in heaving the rhizome out to the ground. Do not pull iris apart in division, but use a sharp knife, dipping the knife into a water/bleach mixture (10% liquid bleach/90% water) between each cut.

Beardless iris differ in that they should be planted in fall or early spring. The roots should never be allowed to dry out while they are out of the ground and they should be watered heavily after transplanting.

Bacterial soft rot was my enemy over the past two years because of not enough drainage in the spring and too much water. It may enter the rhizome through any wound, including feeding damage from Iris borers. To get rid of the soft rot, dig the rhizome, scrape out the affected tissue, allow the Iris to dry in the sun, then dip in the 10% solution of household bleach (e.g. Javex) (90% water) for a few minutes. I even sprinkled the wound with dry bleach cleanser before planting (e.g. Comet).

The most serious pest is the Iris borer. After the eggs hatch in late April, the tiny caterpillars crawl up the iris leaves and begin mining their way down the leaf fold into the rhizome and continue feeding sometimes reducing the rhizome to a hollow shell. Mid-August, the borer crawls out, pupates, becomes a gray brown moth and lays its eggs in debris to start all over again in the early spring. Eliminate eggs by removing and destroying the debris in around the Iris planting both in fall and spring and in July and August, dig up the infested rhizome and physically remove the borer and replant it after using the 10% bleach solution and removing any rotted area.

Japanese Iris thrive in constantly moist soil or even standing in water, while Siberian Irises can tolerate moist conditions as well as those of a typical perennial border. They require fertilizations through the growing season and can go for years without dividing and transplanting.