There are many different kinds of iris in southern gardens. The Japanese, Siberian, and Louisianas do well in moist soil, and the Dutch iris put on a glorious display in April and May in a well-drained location.
The bearded iris—the most popular in America today—needs special care to do well south of Montgomery, Alabama; West Point, Georgia; Shreveport, Louisiana; Jackson, Mississippi; and in the coastal section of the Carolinas.
You can grow these irises easily in the Upper South, but growing them to perfection requires understanding.
How To Grow Bearded Irises
Like many other perennials in the Upper South, bearded iris grows vigorously in the spring, goes dormant during the summer heat, has an important growing season in fall, and then dormant again in winter.
Because of this seasonal growth habit, you must transplant the iris right after flowering while they are in full growth or—better yet—just before the fall growing season starts. Dormant rhizomes transplanted in the hot summer are reluctant to bloom the following year.
Time fertilizer applications to take advantage of this seasonal growth. There is little point in fertilizing during the dormant summer season when there is not enough moisture for plant growth, and fertilizing in late fall produces soft rhizomes that are subject to damage from freezing and thawing.
The best times to fertilize are in early spring and late summer, just before growth begins. Apply several light feedings at weekly intervals.
Here in Tennessee, we use a 3-9-6 fertilizer or a combination of organic nitrogen and a 0-12-12 fertilizer.
Please don’t overlook the minor elements, especially boron and iron in chelated form; they contribute much toward the plant’s general health.
The iris borer has made a sporadic appearance here. Still, this pest is easily controlled by spraying in early spring with DDT, malathion, parathion, or methoxychlor, with a liberal quantity of a spreader-sticker added to the insecticide to hold it on the foliage better.
Three diseases common to tall bearded iris may become quite serious in the Upper South. Leaf spot never kills a plant, but it can make it unsightly.
Captan and party are the most effective remedies if sprayed on the leaves before the fungus appears.
If the disease takes hold, trim back the leaves and burn the trimmings, then spray the new leaves with the fungicide you select to prevent reinfection of the foliage.
Mustard seed fungus usually appears during or just after the flowering season. The best cure for it is the sun. Trim back the foliage and clean up the plants so that sun can reach the leaves and rhizomes.
The third, and the most serious disease, is soft rot (Bacillus carotovorus). The spores that cause it are always present on the soil surface and attack if winter injury occurs or if weak growth develops due to too much nitrogen in the soil.
Soft rot may spread from plant to plant in wet weather, so try to localize it when you first notice it.
A simple and effective remedy is to trim the leaves, remove all affected rhizomes, and water the remainder of the plant and the soil around it with undiluted Clorox.
In severe cases, it may be necessary to dig the clump, clean, trim, disinfect and replant the iris into clean soil to be safe.
Five Factors To A Healthy Iris
Five important factors to the healthy iris in the Upper South— or anywhere:
1. Provide good drainage. Plant in raised beds or hill up single clumps.
2. Do not over fertilize, and be sure the minor elements are present.
3. Plant in the sun as the best prevention against disease.
4. Make a dust mulch around the plants to keep down fungus spores and disease germs and to help hold moisture in the soil.
5. Keep the plants clean—old flower stalks and half-dead leaves are breeding places for trouble.
Could you get rid of them promptly?
44659 by Geddes Douglas