TB, AS YOU WERE

BEARDED IRIS CULTURAL DIRECTIONS

by Ann Cline

GROWING CONDITIONS:

Lots of Sun
Iris like lots of sun, at least 4-5 hours of sun a day. Plants grown in deep shade may not bloom.

Well-Drained Soil
Irises will rot if allowed to stand in water, so benefit from well-drained soil. Plant rhizomes just below the surface in sandy soil or even with the surface if soil has more clay or less drainage. Irises are a very good drought-tolerant plant and like the sun directly on the rhizomes to keep them dry. The soil around the rhizome needs to be firm, to anchor the plant. For clay soil add gypsum (bearded iris like the calcium), or Canadian peat moss to loosen soil.

Neutral To Slightly Alkaline
Bearded iris like neutral to slightly alkaline soil (Siberian and Japanese irises like a neutral to slightly acid soil). If soil is acid, add lime to increase alkaline

WHEN TO PLANT OR DIVIDE

The ideal time to divide irises is one month after bloom and the best months to plant irises are July through September. Irises planted in July have more time to become established before winter, but avoid planting during excessive heat periods.

Distance Apart
Plant rhizomes 2 ft. apart, as each rhizome will become a clump in two or three years. When planting a rhizome, place the "toe" to the front of the garden and allow room for the increases off the back of the rhizome. Three rhizomes placed in a triangle with the "toes" facing (even touching) the center make very nice landscaping clumps.

Dividing Clumps
Divide clumps every three to five years, depending on the plant increase. Cut and replant newer rhizomes from the "mother rhizome." Discard the "mother rhizome" because older rhizomes become woody and are more susceptible to rot and disease. Rhizomes can dry out for weeks without damage to the plant, although this may affect bloom the following spring. If rhizomes have been sitting in water, let them dry for a day.

CULTIVATING AND WATERING

Use shallow cultivation to avoid damaging the roots. Keep iris free of weeds and neighboring plants, so sunlight and air circulation can keep rhizomes dry. Although drought-tolerant, irises do best with one inch of water per week, especially if newly planted or during dry spells.

FERTILIZATION

A good year round fertilizer for iris is 5-10-10. A fertilizer higher in phosphorus and potassium (the second and third elements listed) promotes bloom and root growth. Do not use manure or heavy nitrogenous fertilizers (the first element of the three elements listed) because high nitrogen fertilization may promote soft rot. If wood chips are used around rhizomes, a little more nitrogen may be used because the wood draws the nitrogen out of the soil. Irises love virgin soil (where irises have not grow before) and new, good garden soil does not usually require fertilizing. Do not overdo fertilizing or place any fertilizer on the rhizomes. Alfalfa granules or pellets are an ideal natural fertilizer.

REMOVING LEAVES and BLOOM STALKS

Only cut green leaves back in late fall or when transplanting, as the plant needs the leaves for growth. Remove brown or withered leaves anytime and cut the bloom stalks at the base after bloom.

LIFE CYCLE

Spring (Spring Bloom)
Active leaf and flower growth starts in early spring and growth continues through the bloom season. Each rhizome will only produce one bloom-stalk; then passes the task on to one or more of the new increases it produces After all blooms have faded on a stalk, cut the bloom stalk at the base.

Summer
After bloom, the plant is dormant for a month (except rebloomers) while the rhizome ripens. Unless hybridizing, remove pods from plants, because the pods drain energy from the plant. The new roots begin to form and tiny buds show on young, vigorous mature rhizomes and these increases continue until frost.

Fall (Fall Bloom - Rebloomers)
The rhizomes will act as a food reservoir and the new increases will be next years’ bloom.

WINTER PROTECTION

Newly planted iris will benefit from winter mulch in late fall. Iris can withstand freezing temperatures, but damage may result from heaving and breaking of roots due to thawing and freezing in late winter or early spring. Heaving may result in loss of bloom or plant. Good mulch is sand, and should be removed in early spring.

WEED CONTROL

Preen, which prevents seeds from germinating, will not harm iris.

IRIS CHALLENGES

Root Rot
Root rot may be caused by excessive water conditions, poor drainage, or an acid soil. Remove the soft, rotten portion, dust "cuts" with powdered bleach, and expose to the air and/or sun to dry the rhizome before replanting.

Iris Borer
The iris borer follows four stages:

  1. Egg
    Eggs winter over on lower parts of stalks, leaves, or debris near the ground, or in the cracks of rhizomes. Good fall and/or spring clean up and disposal of debris will eliminate many eggs. Never compost iris leaves.
  2. Larva
    The borer is pinkish-white with a brownish-red head. There may be more than one larva per leaf and more than one leaf per fan may be infected. But, as the borers eat their way down into the rhizome, only one borer will survive as the biggest borer eats the smaller borers. While the borer is still in the leaf is the best time to eliminate the borer by spraying foliage and plant with Bayer's Advanced Lawn season-long Grub Control in the early spring when the Forsythia begin to bloom (April in the Detroit area). The key ingredient is "Merit" (must list Merit), and is very effective against iris borer. It comes as a liquid, just attach the blue plastic bottle to the garden hose to spray or use granules to sprinkle around the plant, then water.
  3. Pupa
    When newly tunneled borer holes are found in the rhizomes, but no larvae, search the soil for pupae which looks like a shiny, slender brown nut.
  4. Moth
    The moth lays its eggs in the fall. The black moth has brown fore wings marked with black lines and whitish-tan hind wings. Because the moth is nocturnal, it is rarely seen.
Leaf Spot
Although unsightly, leaf spot usually will not kill the plant, but may affect the plant growth. It occurs in wet weather, but generally stops during warm, dry weather. To combat, start spraying in the spring, six weeks before bloom and regularly each week (respray after rain) as lighter spots (which turn brown) appear on leaves. Spray with Zineb, Dithane Z-78, Parzate, Dupont fungicide "A", Orthocide Garden Fungicide, or Fermate.