Iris, the goddess of the rainbow in Greek mythology, is a fitting name for plants that bloom in a multitude of colors.
The irises used most often in gardens, according to The American Iris Society, fall into three main groups: Bearded, aril and beardless. This article focuses on the bearded iris.
The bearded iris is a hardy perennial that requires little maintenance. Swordlike leaves grow in a fan shape and sturdy flower stalks hold the six petaled flowers — three upright petals, called standards, and three hanging petals, called falls — with a fuzzy beard that runs down the middle of each fall.
The height of the iris determines its class — miniature dwarf, no taller than 8 inches; standard dwarf, 8 to 16 inches; and tall, over 27.5 inches. The intermediate, miniature tall and border classes all grow to the same height of 16 to 27.5 inches, but additional aspects determine to which class they belong. The classes also have a range of bloom times from as early as March for the miniature dwarf, to June for the tall. By planting different classes, you could have irises blooming for several months.
The bearded iris grows from a rhizome, which looks like a fleshy, elongated, misshapen potato, with roots that grow from the bottom. The rhizome is where food is produced and stored.
Before planting, consider testing your soil to ensure the best start for your iris. Plant your iris in late summer to early fall in a sunny, well drained spot, to avoid holding moisture that could cause the rhizome to rot. Dig a hole wide enough to accommodate the roots and form a mound in the middle for the rhizome to sit on, spreading the roots in the trench area around the mound. Fill with soil, leaving the top of the rhizome slightly exposed, and water thoroughly.
Once your new iris is established, avoid overwatering. Do not mulch, because that could hold moisture and cause the rhizomes to rot.
Fertilizing is not usually necessary but if you do, apply a general 6-10-10 fertilizer, or bone meal, around the time tulips are blooming. Be careful not to get the fertilizer on the rhizomes to prevent injury but work into the surrounding soil.
When irises bloom, they usually have several buds on a stalk.
As the flowers fade, carefully remove the spent flower. When all the flowers on a stalk have died, cut the stalk off at the base. Remove any diseased leaves that may appear.
In late fall, cut back the foliage to about 6 inches and clean all debris to avoid overwintering of disease or insects. If a harsh winter is expected, cover with evergreen boughs or straw. Remove winter cover promptly in spring.
Several diseases and pests can damage irises. The most important step is prevention. Keeping the garden clean is the best defense against disease and pests.
Remove old iris leaves and stalks, especially in the fall. This is where the eggs of the iris borer, the most damaging pest of the iris, overwinters. Eggs hatch in April or early May, then little white caterpillars crawl up the new leaves and bore into them, eating their way down inside the leaf until they reach the rhizome. When mature, they are pinkish colored with brown heads and they eat their way out of the rhizome, to pupate in the soil into adult moths. As the larvae bore down the leaf, the leaves look ragged and water soaked. If you notice this early enough, you can squash them inside the leaves with your fingers. Once the borer is in the rhizome, the leaf damage is extensive and the plants will need to be dug up, disposing of any rotted or damaged rhizomes and killing any larvae.
Aphids can suck the sap out of the leaves. Pick them off by hand and put into soapy water, or spray them with a mixture of dish soap and water, which will suffocate them. Crickets, pill bugs and voles are also pests that may be attracted to an iris.
Diseases include bacterial leaf blight, characterized by faint, water-soaked spots; bacterial soft rot, leaves collapse suddenly or die from tips, rhizome has a foul odor; fungal leaf spot, small brown spots with water-soaked margins; botrytis rhizome rot, few leaves in spring, then turn yellow, brown and die.
After several years, as the rhizomes multiply, you may begin to see fewer blooms. Then it’s time to divide the clumps. Late summer or early fall will give the divided rhizomes time to establish new roots before winter.
Prepare any new beds before separating your iris. If planting in a new area, soil testing is recommended. Carefully dig up the clumps (deep enough to not cut off the feeder roots), shake the soil off and separate the individual rhizomes by pulling apart, or carefully cutting with a sharp knife. Any cut areas should be left to dry overnight. Each section should have a healthy fan of leaves and firm white roots.
Discard any soft or rotted rhizomes or those that have no visibly healthy roots. Cut leaves to about 5 or 6 inches. Plant in the same manner as new plants.
With a little maintenance and a few years of dividing, you can enjoy a rainbow of irises in your garden for years.