Louisiana Iris Growing Tips and Culture

Louisiana Irises Growing Well

The general garden culture of Louisiana irises is fairly simple.  While these irises do have a few preferences, they are not difficult to satisfy.  

Louisiana irises are adaptable to most parts of the country.  Although the preponderance of the irises found in the wild occur along the Gulf Coast, two of the five species are indigenous as far north as Illinois, Indiana, Ohio and Kentucky.  One, I. brevicaulis, is found in Ontario.  Experience with Louisianas in colder climates has been good.   There is a very successful public planting of Louisiana irises in Highland Park in Rochester, NY, for example, a spot some might have thought too cold.  

Some cultural practices are constant regardless of latitude, and others need to be modified.  More has been written about recommended growing practices in the South, and Zydeco Louisiana Iris Garden is located in New Orleans, which is challenged by only about an inch of snow every ten years.  The experience underlying the following observations and suggestions is decidedly southern, but information on other climate conditions will be noted when known.  

The Culture Resources link will take you to growing tips specific to other regions and states and to varying growing conditions.  Propagation techniques for Louisiana irises are discussed on a different page as well.

General Location

The low and wetland origins of the native species should not imply that Louisiana irises require aquatic culture.  They do love water and thrive in ponds and boggy settings, but Louisianas also grow and bloom exceedingly well in typical garden beds. These irises should not be allowed to dry out during periods of drought, however. They will stay green and grow through hot weather only with ample moisture.

Louisiana irises should be grown in half to full sun.  Less than a half day of sun will diminish bloom.  It is highly advisable to avoid close competition with large trees or plants with extensive root systems that would use most of the soil moisture.  In hot climates, unless the irises are in ample water, full sun may stress the plants at certain times of the year.

Louisiana irises can be mixed with most smaller ornamental plants.  They also can be grown in beds consisting entirely of irises, although iris-only beds may not be as attractive in late summer as the foliage begins to die back in preparation for the new growth cycle that begins in the fall.  Any yellowed foliage can and should be removed to improve appearance and encourage new growth.

Soil Conditions and Preparation

An acid soil is often recommended for Louisiana irises, but this is not necessary. Soils in much of the Gulf Coast are acid, but some areas, such as parts of New Orleans and the Mississippi River flood plain, may be neutral or a bit alkaline. Since Louisiana irises were found in the wild in these areas, they had to be happy with the natural conditions.  However, Louisiana irises grown in very alkaline soils, such as in some Western states, will exhibit yellow leaves and stunted growth. There has been no systematic test of the limits of tolerance in an acid or alkaline direction, but experience in the 6.5 to just over 7.2 range has produced excellent results.

Irises need a soil high in fertility and organic matter.  Finely ground pine bark, composted oak and other leaves or rotted manure, for example, are excellent additions that should be worked into the soil when beds are made.

If the soil has a clay texture, adding some sand may be helpful.  Although these irises in the wild may be found in clayey muck, a loose and friable soil is helpful in promoting growth and bloom in garden conditions, provided that the irises do not dry out.  

If the irises are grown in water instead of a garden bed, there are other factors to consider.   With any container placed in a pond, a soil too light may tend to float away.  Store-bought soils and amendments, unless designed for aquatic culture, may not be well adapted for pots immersed in water, and a heavier soil is advised.  In water culture where the appearance of the water is not an issue, such as in natural ponds or large containers not intended to fit into a naturalistic pond setting, a wide variety of soil types seem to work well, from nearly soil-less mixes to typical garden soil.

If possible, prepare iris beds a few weeks before planting, but don't fret if you have to plant immediately.  The traditional recommendation is to add the organic material (2-3 inches) and a generous amount of commercial fertilizer (for example, 8-10 lbs. per 100 sq. feet of 8-8-8) to the bed, and work in.  An azalea/camellia fertilizer is a good choice if there is a need to adjust for an excessively alkaline soil.  Organic fertilizers are also effective, although the amounts equivalent to a balanced chemical fertilizer are difficult to estimate, and not much guidance is available specifically applicable to Louisiana irises.  If you want to use organic fertilizers, however, a Georgia Cooperative Extension publication may be useful (no longer online, but the link is to a pdf version).

Planting and Dividing

Unlike most plants, which go dormant or grow little in the winter, the growth cycle of Louisiana irises in their native range actually begins in the fall, continues through winter and culminates in a burst of rapid growth and bloom in the spring.  When the weather gets hot, growth may slow or even stop, especially if moisture and soil fertility are not optimal.  In the north, the winter growth may not occur, and snow and cold will interrupt growth cycle.  Whereas bloom along the Gulf Coast may begin in mid-March, it may be delayed until June in attitudes such as the Upper Midwest.

Timing. Consistent with irises' growth cycle, the best time to plant and divide Louisiana irises along the Gulf Coast is mid-to-late August, September, October, not long after the period of new growth has begun. Irises planted later than November are not likely to become well enough established to reach normal size and bloom in the spring.In cold climates, fall planting is also recommended, but early enough to let them establish before the coldest weather.  August and September are the preferred months.Transplanting immediately after bloom is not recommended. The hot weather following closely upon the bloom season will stress the plants, and little growth or even an early dormant period may result.  The longer into the season foliage growth can be continued, the better the chances of good bloom the next year, because the plants have a greater opportunity to grow larger rhizomes to support bloom.  If it is necessary to transplant after bloom, be sure to supply extra water.   Alternatively, hold the irises over in water, or in pots set in shallow water and partial shade, until new growth has resumed or until the fall planting season. Growers in such warm climates in South Florida report that Louisianas can be divided at any time of the year.

How to plant Louisiana irises

Placement. Irises should be planted with about ½ to 3/4 inch of soil covering the rhizome and, ideally, 1-2 inches of mulch over the soil. Planted about 12 inches apart, Louisiana irises can be left in place 3-4 years and will form clumps.  Every several years, it is helpful to dig and divide the irises, thinning them out and replenishing the soil with organic matter as if preparing new beds.

Remember that the rhizomes grow longer as new leaves emerge, and varieties planted too close together will become mixed and difficult to identify.  The rate of "traveling" varies with the particular variety, since the typical size of the rhizome varies.  Two or more offsets generally form each year on either side of the rhizome, and their growth extends roughly perpendicular to the original rhizome, which results in the tendency for a clump to develop.  Each rhizome blooms only once, then the offsets bloom in subsequent years.  Keeping this grown pattern in mind is helpful in deciding where to plant Louisiana irises.  (Plants produced as offsets will be identical in every respect to the parent rhizome; plants grown from seed will vary, perhaps markedly, depending upon the identity of the particular parents).


Watering is often necessary to achieve a sufficient growing season for good bloom. The beds should not be allowed to dry out. September and October are relatively dry along the Gulf Coast and it is important to give the iris beds a thorough soaking at least once weekly during such dry periods.  In summer, a dry spell without good watering will cause growth to halt or even cause the plant to go dormant.


In truth, fertilizing practices vary a good bit among Louisiana iris growers.  The traditional advice has been:  For new or replanted beds (to which fertilizer and organic material have been added at planting time), a light dressing of a complete fertilizer (2-4 lbs. per 100 square feet) is sufficient about two months prior to bloom (late January in Louisiana).  Beds which have not been replanted in late summer are generally given two applications, a fairly heavy one at the start of the growing season, and then the light dressing just before bloom.  Complete fertilizers such as 8-8-8 are said to be preferable to high nitrogen fertilizers.  High nitrogen can cause the plants to produce leafy growth while suppressing flowering; it also is thought to render the plants more susceptible to some diseases.  An acid-forming azalea/camellia fertilizer should be used if the soil tends to be too alkaline, as in parts of the West.

Many serious growers of Louisiana irises deviate from this recommendation in several respects.  Some recommend a third feeding after bloom. Some favor liquid fertilizers, and some select fertilizers with additional nitrogen. Timed-release products are occasionally recommended, especially in water culture.  

We do know that Louisiana irises are heavy feeders, and there is little doubt that the average gardener fertilizes them a good bit less than optimal.  Failure of foliage to remain pretty and green in the hot months after bloom probably is due to insufficient water and less than optimal nutrition.  Cases of problems from over-fertilizing are rare, but the complaint that "my irises did not bloom" is often associated with failure to fertilize.


Mulching is an important part of good culture.  Mulches serve many purposes, such as maintaining soil moisture, keeping weeds under control, increasing organic matter in the soil, and protecting against sun scald (see below).  About 2-3 inches of rotted or even fresh leaves, pine straw or pine bark are excellent mulches.  Materials available locally, such as bagasse (sugar cane fiber), should be considered.

Diseases and Pests

In their native range, Louisiana irises are not prone to many diseases and insect pests.  Most growers are able to easily endure any small nuisances without having to resort to insecticides or other treatments.  In other sections of the country, some additional problems are reported, and the grower is advised to seek information on local conditions.  Some the links on the Culture Resources page may be useful.

Examples of rust infestation of Louisiana irises

Rust appears as red to dark-brown powdery spots, often surrounded by a yellow margin, on leaves and stems.  Leaves may become severely discolored and die back. The rust does not appear to damage the plants severely, but it does make the beds look bad.  Avoiding too much fertilizer, especially high nitrogen, is said to potentially limit the spread of rust.  Some growers feel that cow manure, specifically, may promote rust.

The best way to avoid rust is to remove and discard withered leaves.  Rust is a soil borne fungus, and if infected leaves are not permitted to decay in the garden, the life cycle of the fungus is disrupted.  Stands of Iris fulva in the wild are often infested with rust.  This is not due to gardeners who applied too much nitrogen, but rather by their unavailability to clean up and dispose of the infected foliage.

If an infestation of rust does begin, it is important to remove affected foliage to the extent possible (put it in the garbage can, not the compost pile).  Some growers recommend spraying plants in the area of the rust with such products as Ortho's Garden Disease Control or Fertiloam Systemic Fungicide, but there is no substitute for removing the infected leaves from the garden.  If the bad foliage remains, the rust is likely to return the next year; if it is removed, there may not be another outbreak for some years.

Examples of leaf miner damage to Louisiana iris foliage

Leaf Miner is indicated by white steaks along the leaves, particularly near the base, in hot weather.  It is caused by the larva of a type of fly. The outermost leaves may collapse, and, if they become unsightly, can simply be removed.  Leaf miners rarely cause enough trouble to warrant treatment with an insecticide.  

Damage caused by iris borers

Iris borer may be a problem now and then in the Gulf South, but it is more serious to the north and in areas where bearded irises are grown.  The worm enters the rhizome and may hollow it out and effectively kill it or destroy its ability to produce a bloom stalk.  The first sign of a borer may be a center leaf in a fan that turns yellow and dies.  This occurs because the borer, first deposited on the leaves, has worked its way down to the rhizome and devoured the growing tip.  If one watches for center leaf damage, the borer can sometimes be found and destroyed before the rhizome is seriously injured.  Some chewed or damaged foliage may be evident early, before the borer has reached the rhizome. Sometimes it is possible to gently spread the leaves of a fan and kill the critter before it does real damage.  A rhizome damaged by a borer will often produce offsets unaffected by the problem, so there is no need to discard the entire plant.

Snails and slugs may climb up the scapes and disfigure a bloom, particularly under conditions of high humidity and rainfall.  Some growers use a commercial snail bait and others set out saucers of beer.  Snails are not a problem of sufficient severity that most do anything about it at all.  Those who grow irises for entry in shows may be the exception.

Sun scald is not a disease, but a condition resulting from the sun scorching an exposed rhizomes in midsummer, causing them to become mushy and to deteriorate.  Unlike bearded irises, Louisiana iris rhizomes do not naturally grow along the top of the soil, but usually just below the soil level. Sometimes, especially late in a season, the top of the rhizome may be come exposed.  Adding soil or a mulch solves this problem.

Cutworms are sometimes a problem.  Cutworms are chewing insects that will sever leaves and disrupt growth.  One recommendation is a fertilizer fortified with an insecticide, such as that sold for control of lawn chinch bugs.

Moles and voles are serious problems in some areas.  Some growers have reported growing Louisianas in containers sunk in the ground to prevent the rhizomes from being eaten.  If drainage in the container is obstructed, this offers the added advantage of promoting constant moisture.  This tactic obviously is more work than just digging a hole in a garden bed and planting an iris, and if the container is not sufficiently wide the irises will soon escape as the rhizomes grow longer.