Bearded Iris Culture

Where to Plant

Sun or Shade?  Choose a sunny location that receives minimum half day of sun. In Southern climates, plants will appreciate a bit of afternoon shade to help maintain color and longevity of bloom.
 

Type of Soil

Iris will grow in most soil types. Sandy loam soil is best. Excellent drainage is a must. In heavier soils, raised beds are a beneficial option. Soil ph should be neutral to slightly alkaline (6.5-7.5).
 

When to Plant

After blooming and growing for a period of time in Spring, iris enter a dormant to semi-dormant state. This period from July through October is the best panting time. In areas where winter comes early, planting earlier in this cycle is better. Areas with unrelenting summer heat will do better to plant later.
 

How to Plant

Plants shipped by mail should be removed immediately from their box and laid out so air can easily circulate around them. Plant as soon as possible in fertile, well prepared soil. DO NOT plant too deeply. Cover the rhizome (fleshy part of plant) with ½” to 1” of soil. Water in well to firm soil around the roots. In areas with hot temperatures, placing a wooden shingle or such on the west side of the plant will help protect it from the sun until it begins to grow again. In colder areas, newly set plants will benefit from an airy mulch after the ground is frozen. This will keep the rhizomes from heaving out of the ground due to alternate freezing and thawing. Water sparingly at weekly intervals until vigorous growth begins again. Do not fertilize newly set plants. Wait to fertilize until they are established and beginning their spring growth.

Plant rhizomes at least 24” apart to avoid dividing and replanting too frequently. Annuals can be used to fill the open spaces while clumps are maturing the first year. If a more immediate clump is desired, three or more plants of a variety can be planted. Plant with the toe or cut portion of the rhizome close to each other with the fan or green part at the outer edge of the ring.
 

Maintenance

Controlling weeds increases the beauty of your plantings and also reduces competition for nutrients. Shallow cultivation helps kill weeds and aids air circulation through the soil. Insure an adequate supply of moisture during active growth phase including bloom time. Fertilize as active growth begins in Spring and again after bloom. A soil test is recommended to determine soil fertility and ph. It will also help in selecting the proper fertilizer. Without a soil test, a 5-10-10 fertilizer is a good starting point. As bloom progresses, take off spent blooms to help tidy up your garden. After bloom, remove old bloom stalks. Cut them off just above the rhizome. Trim off dead and diseased leaves and dispose of them. DO NOT cut off healthy leaves, they are producing food for the plant and next years bloom.


Dividing and Replanting

The best quality bloom will normally be the second through fourth years after planting. After this, the clumps become crowded and bloom diminishes. To divide, dig the clump and separate off the largest rhizomes. Trim foliage back by about 2/3 to reduce stress on the plant while it is trying to grow again. Replenish the soil and replant as instructed earlier.


Pests and Diseases

Bearded Iris are generally carefree plants, but there are a few problems.

• Iris borer is a concern in the North and Eastern US. They can be killed by chemical sprays or by observing their activity in the leaf and physically squashing them. Aphids can sometimes be a problem that can be addressed with chemical sprays or with the introduction of predator insects.
   

• Bacterial soft rot causes the rhizome to become soft and has a foul odor. It is more prevalent in Southern climates with hot, humid summers. When soft rot is detected, clean out the soft portions and treat the rest with a bit of lime, chlorine powder, or Dial liquid anti-bacterial soap. In severe cases, the clump may need to be dug, treated, and dried before replanting.
   

• Crown rot or mustard seed fungus is also more prevalent in Southern climates. The rhizome and leaves at ground level begin to soften and are later accompanied by a white cottony growth and later by small mustard seed sized bodies. This can be treated with terrachlor or by digging and destroying the plants. Do not plant iris or other susceptible plants back into this area.
   

• Fungal leaf spot is unattractive but not usually lethal to the plant. This is a soil born pathogen and so good garden sanitation is helpful. Various fungal sprays can be used to help keep it in check. Growing your iris with companion plants around them helps reduce infected soil from splashing on the leaves and so reduces infection. Be sure that the companions don’t become unwelcome intruders that shade out your iris.