Plant Description

Foliage:

Stiff, sword-like, medium green foliage arranged in a fan shape.  Growth comes from center with older, outside leaves withering and dropping off.  Plants are subcategorized by height in bloom, ranging from Miniature Dwarfs (up to 8” tall) through Intermediates (16” to 27”) to Tall (28”) with several additional categories in between.  Rhizomes of larger plants are fat and yam-like.

Bloom:

Iris blooms are composed of six petals, three of which arch upward

(called standards) and three of which arch downward (called falls).

Bearded iris gain their name from an elongated hair-like structure near the base of the falls.  Some bearded iris blooms may also come with ruffled or finely crimped petal edges.  

Bloom Color:

A myriad of colors and color combinations from palest pastels to almost black.  An iris of entirely one color is called a self.  Bicolors have standards and falls of two different colors; plicatas have white/yellow petals with darker color applied around the edge; amoenas have white standards over colored falls. 

Bloom Time:

Spring.  In the Atlanta area, typically over several weeks in May. Usually the smaller varieties are the earliest to bloom.  Some reblooming varieties produce blooms again in August/September.  A reliable rebloomer is pure white ‘Immortality.’ 

Planting:

Propagation:

New plants are obtained from divisions taken from existing plants.  Division should be done every 3-4 years, ideally during the most vigorous growth period right after bloom, but can be done anytime through fall.  Renew the iris bed with compost or other organic material.

Site:

Plant in full sun and in soil with a neutral to alkaline (6.0 or above) pH.  Soil should be moist, but well-draining.  Work soil, incorporating 4-6” of compost or other soil amendments to a depth of 12 to 18”.  Bearded Iris are particularly susceptible to root rot problems from poor drainage.  Planting in raised or on a slope can help take care of this problem.

Planting:

In a well-prepared bed, dig a hole deep enough to accommodate the feeder roots extending from the rhizome.  Build a mound in the center of the hole that will bring the rhizome to soil level and allow the roots to drape down into the hole on either side.  This is a good time to add a handful of time-release fertilizer to the hole.  Fill in the hole until 2/3 of the rhizome is covered by soil.  Firm the soil around the roots.  One third of the rhizome should be fully exposed (think of an alligator floating in a stream).  After watering in, check the planting levels again.

Bed Planting vs. Clump Planting:

When irises are planted in individual beds, make sure that all the rhizomes are facing the same way, for example, uphill. When planting in mixed borders, clumps are the preferred planting scheme.  Create a triangle of three plants, two growing outward and the third growing into the space in between.  Space the tallest of bearded irises 12” apart to allow for growth and good air circulation.  Smaller iris may be planted more closely together.

Maintenance &        Division:

Maintenance:  Maintain good garden sanitation by periodically picking up and removing any withered leaves and bloom stalks to avoid disease and pest problems.  Remove easily loosened leaves from the outside edge of the iris “fan.”  If the plants are disease free, this material may be used in the compost pile.  Otherwise, it is best to put it in the trash.                                                                                                                              Division:  Divide Bearded Iris every 3-4 years to prevent bloom decline.  Lift the rhizome from the ground  and examine it for disease. Cut away any old, nonproductive tissue, leaving just the actively growing 2—3 inches at the tips of the “fingers.”  Make sure that each new individual rhizome has at least 2-3 feeder roots attached. Cut back the foliage of the fan to 4-6” (traditionally this is done in a triangle shape with the point facing up).  Replant your iris as above, spacing at least 12” apart.  You will probably have more than you need.  Enjoy giving them to neighbors and friends!

Fertilization: 

Bearded Iris growing in rich, well-draining garden soil should need little fertilization.  A handful of slow-release fertilizer or an application of compost or composted cow manure per plant at the beginning of the growing season (mid-March) will provide enough nutrition.  Avoid over-application of nitrogen, as it causes lush, weak foliage growth but can prevent blooming.

Problems:

Disease:

Bacterial Soft Rot:  Usually found in irises grown in poorly drained sites or with too much mulch (leave top 1/3 of rhizome uncovered!).  Characterized by toppling leaf fans, mushy rhizomes and disgusting odor.  Dig rhizome, scrape out affected tissue, allow to dry in sun, then dip in a solution of 10 % household bleach for a few minutes.  Rinse with water and allow to dry before replanting.

Iris Leaf Spot:  Fungus that attacks leaves, but not flowers and roots.  May weaken plants by leaf loss.  Overwinters in old, decaying foliage.  Practice good sanitation by removing all old foliage and cutting any diseased leaves to the ground.  If disease is persistent or very widespread, spray with a fungicide containing clorothalonil or mancozeb when leaves are 4-6 inches.  Repeat every 10 days.  Be sure to add ¼ teaspoon liquid detergent to a gallon of spray to aid in wetting the waxy foliage.

Pest:

Iris Borer:  caterpillar larvae of moth egg deposited in fall on old iris leaves and debris.  Hatches in spring and eats through new green foliage to center of rhizome, often fully destroying it.  Careful clean-up of organic debris in late fall and early spring can help limit infestations.  Individual borers may be eliminated manually by pinching just below notch in leaf edge which signals borer entry, thus crushing borer.  Borers that have reached the rhizome may be skewered by inserting a wire into the entry hole in the rhizome. Severe infestations may have to be controlled by spraying in early spring (leaves 4-6 inches tall) with a product containing dimethoate.  Two applications are usually necessary.