Growing Iris Plants in the Summer

The Greeks named the flower after their god of the rainbow, Iris. These early Greeks often planted irises on graves, since it was the duty of the god, Iris, to lead the souls of dead women to paradise. The many colors and forms of iris make it possible to create a corner of paradise in the garden. Late summer is the best time for starting a new iris bed or for reworking an old one.

The most popular of irises is the German or bearded iris that grows from a thickened underground stem called a rhizome. This structure usually grows parallel to the soil surface and just slightly under it. The true roots extend into the soil from it. Before planting iris, good soil preparation is important. Since most iris need transplanting only about every 3 or 4 years, soil should be in good condition before a permanent planting is made.

Although some iris, such as the Japanese iris, like moist locations, the popular garden types need excellent drainage. They flower best in a sunny location. Dig the soil for the bed deeply, and remove any grass that may have been growing in the area. At the same time the soil is dug, a complete garden fertilizer should be applied at a rate of about 2 to 3 pounds per 100 square feet. If the bed is a new one with unknown fertility, have the soil tested to determine more exactly what additions may be needed.

When iris have become overcrowded, the center of the clump often becomes weak while the outer portions are vigorous. The central portions should be discarded and only the most vigorous sections replanted. Before replanting, pull off all dead or dying foliage, and cut back the tops to leave about one third of the original height of the fan. At the same time the sections are being cleaned for planting, inspect for presence of insects or disease.

Iris do not have many problems. However, there are three that should be watched for. These are leaf spot, bacterial soft rot and iris borer. Leaf spot rarely kills a plant, but it may weaken it. It is first seen on the leaves as small oval spots with a water soaked margin that eventually turns yellow. If the spots are numerous, the lips or entire leaves may be killed. If present, clean up and destroy badly infected leaves. Spray with a fungicide such as zineb or ferbam in the spring at about weekly intervals up to flowering.

Bacterial soft rot is a very destructive disease. The rhizome or leaf base is attacked. Plants become weakened and yellow and finally die. The rhizome becomes a soft, rotten mass and, when broken open, has a very bad odor. If the disease is present, dig and destroy infected plants. Cut partially damaged rhizomes back to good tissue. Do not plant these pieces promptly, but allow them to lie in the sun for about two days to let cut areas dry thoroughly.

Do not replant them in infected soil. The iris borer is an insect that lays eggs in the fall, but the tiny caterpillar does not hatch out until spring. At that time it crawls up the leaves and enters them. It eats down through the leaf and into the rhizome, where it eats out the center. This weakens the rhizome and, if it is not killed directly, makes a good entry for soft rot. Clean up debris in late full and again in early spring to help get rid of the eggs. Spraying with an insecticide in late April and early May can help kill larvae before they have entered the leaves.

http://en.wikipedia.org/wiki/Iris