FAQ - Plants - Louisiana Iris

Louisiana Irises are among the most favored of the bog plants. Their foliage is attractive and is useful as a backdrop, or as an adjunct to the other plants in the bog. Their flowers have an obvious appeal, being among the most exotic flowers in the hobby. The plants are useful as filtering agents in ponds and can be grown in any moist area, making them useful as transitional plants between the pond and the landscape because they can be planted along the pond’s edge or directly in the water itself.

The term “Louisiana Iris” refers to any of a large group of beardless Irises that are either one of five wild species, natural hybrids of those wild species, or hybrids achieved by the painstaking work of enthusiasts all over the world. The work of these people has given us forms that vary greatly in size, color, form, and bloom time. Experiments have been performed using colchicine and other agents to achieve “polyploidism,” or the multiplying of chromosomes, in Louisiana Irises. These experiments have led to many of the more stunning varieties, with improvements in flower size, petal substance, and bud count per inflorescence.

Taxonomically, Louisiana Irises belong to the family Iridaceae, genus Iris, subgenus Iris, section Spathula, subsection Apogon (beardless), series Hexagonae. The taxonomy of the Irises is still being sorted out, but this is the way it stands now. Related members of the Apogon, or beardless, group are the Laevigatae (Japanese and other moisture-loving Irises), Sibiricae (Siberian Iris), Spuriae (Spurias), Californicae (Pacific Coast Irises), and 10 other series of less well known Irises.

The normal geographical range of the native species extends from the Gulf States up the eastern seaboard into the Carolinas and west to the Mississippi River Valley. There are five primary species involved in the mixing. They are I. fulva, from which we get all of the red varieties; I. giganticaerulea, from which we get the larger blue and white hybrids and varieties; I. brevicaulis, from which are derived the purples and smaller blues; I. hexagona, from which we get many lovely purple hybrids, and I. nelsonii, a natural hybrid of I. fulva and I brevicaulis that has been around for so long that it has achieved the status of an individual species. We get many yellows from this species.

These species and their many naturally occurring varieties have been merrily mixing it up for centuries in an area that has been termed the “Golden Rectangle” of Irises, affording enthusiasts a rich heritage to draw from. The “Golden Rectangle” is a small area that comprises all of southern Louisiana from the Mississippi River delta west to the Texas-Louisiana state line and extends about 100 miles inland. In this area, climatic and geographical forces caused the confluence of the ranges of the five basic species. One of these species, I. nelsonii, is the result of a cross that occurred in an isolated area long enough ago for the result to have achieved the status of an individual species. At the time of their “discovery” by enthusiasts, the area around New Orleans was a scene of spectacular beauty every spring with millions of Iris flowers gracing all of the swamps and lake margins in the area. Early collectors were very fortunate indeed to have seen such a thing (read John Muir’s description of the wildflowers of the central valley of California) and to have had such a resource to draw from.
Unfortunately, destruction of Iris habitat by humans has led to the demise of most of these natural populations, leaving us the collections of enthusiasts to serve as a resource to draw from. And what a collection they accumulated! For several years the annual meetings of the local Iris groups included collecting trips that ranged throughout the area. Hundreds of varieties were collected from the 1920’s to the 1940’s, but only relatively few of the collected varieties proved to be useful as hybridizing stock. Current varieties include white, lavender, blue, yellow, red, purple, bicolors, ruffled petals, smooth-edged petals, doubles, rebloomers, small and large flowers, and tall or short plants.

Louisiana Irises are rhizomatous, meaning that they form a specialized, thickened stemlike structure that creeps along the substrate, producing fresh leaves from the leading end (apical bud) and branching to varying degrees behind the apical bud. Other examples of rhizomatous plants in the aquatic plant world include pickerel plants (Pontederia), Thalia, Marselea, and many species of Sagittaria. The rhizomes of some varieties branch heavily, eventually creating colonies of plants in which the rhizomes are crossed over one another two or three deep. Others branch more reservedly, forming more open colonies of less tangled growth.

All of the varieties and species in this group tolerate a wide variety of growing conditions, ranging from total inundation of the rhizome under several inches of water for months at a time to living well above the water line in areas that dry out from time to time. Of course, they prefer the conditions in which there is always plenty of water, but they will tolerate some lack of water once established. Southern California has been described as a paradise for Louisiana Irises because of our mild winters and long growing season.

They will also tolerate many different soil types. In areas where they are to be grown out of the water, they prefer a rich, sandy loam, with plenty of mulch. Kept moist and given proper light, plants in this soil type will achieve full height and bloom profusely. In areas where they are to be grown in shallow water, they prefer sandy, loamy soil with less organic matter than when grown on the ground. Frequently, normally occurring pond detritus collecting around the roots as the colony grows works best. For starting out fresh, though, I prefer to mix soil, making sure to add plenty of composted pond mud and timed- release fertilizer (Osmocote 14-14-14). I also add a small measure of bone meal to the soil to give stronger roots (more divisions) and larger flowers.

Here in southern California, new leaves begin to come on in November, with earnest growth beginning in December or January. New growth continues through the winter, with new branches of the rhizome putting on a lot of size in preparation for the spring bloom. In colder climates, this process is delayed until the spring thaw. Some time in February or March, depending upon the weather, the situation, and the plants’ genetics, plants will begin to form inflorescences. In general, the warmer the situation, the earlier the onset of flowering will be. A few varieties, especially “Clyde Redmond,” will rebloom in the fall, but for the most part, what you see in the spring is what you get for the entire year. As mentioned above, actual bloom time is also controlled by genetics. Some of the original species bloom at slightly different times, which gives us the “early” and “late” blooming cultivars. Each inflorescence lasts a couple of weeks, with the entire blooming season, including early and late bloomers, ending by the first week of June. I have never had one in bloom at the Del Mar Fair, which begins on June 15, but I have missed it by a matter of days on a couple of occasions.

As the flowers finish, you should remove the old inflorescences, unless you wants to make seeds. The plants will continue to produce new foliage until late summer, when the older leaves start to die off. This will continue into November/December, when the new fans begin to show.

Louisana Irises are relatively easy to care for. If they are in the right place, they are fairly disease- resistant and are susceptible to only a few pests.
First and foremost is good air circulation. There are a couple of reasons for this. One is that Louisiana Irises are susceptible to a rust-like fungal infection that will eventually destroy the plant all by itself, or cause the plant owner to just throw the plant away in disgust. Rust is introduced by spores coming into contact with the leaf. This may be accomplished by the wind, by the feet of ants, or by contaminated blades or hands. The best way to avoid contamination by this disease is to keep the bed of plants from becoming too crowded, and to avoid areas of low air circulation. Regular spraying with light oil and an appropriate fungicide is a good idea, as well. Also, I always try to remove the leaves as they die completely. Sometimes, though, aesthetics demands that the leaves be removed before they are completely dead. I hesitate to do this because pulling or cutting them off before they are completely dead opens wounds that seem to me like open invitations to infection. Spraying plants that have just been cleaned with oil/Funginex solution (see below) is a good idea.

The other reason to maintain good air circulation is that white flies and/or scale insects may attack Irises. Ants bring them in and under the right conditions they will proliferate, causing all of the familiar problems associated with these insects. Most of these problems can be dealt with by using commonly accepted practices of good gardening.

The rust is the most intractable problem and should, therefore, be anticipated and hit head on when discovered. I have had some success with a mixture of paraffin oil (sold as “Ultra Fine Oil” or as “Sun Oil”) and Funginex. This must be applied every couple of weeks through the growing season if the disease has been spotted, and less frequently if it hasn’t. The problem seems to occur most frequently if the humidity is high.

When planting Louisiana Irises in water, I have found that trays set at an appropriate depth are the best container to grow them in. The reason for this is simple. Since Louisiana Irises are rhizomatous, they require some floor space to move around on, and a tray provides this. If they are in a tall pot two things will happen. One, the plant will quickly reach the edge of the pot and try to grow through or over the side. If it succeeds in getting over the side of the pot, it immediately tries to head downward to follow the substrate. If it finds no substrate, it will eventually rot away. If it doesn’t get out of the pot, it piles up against the side and rots in a tangle under the mud. Also, a deep pot is so deep that the plant will never use all of the soil, whereas in a tray, the roots eventually fill the tray, so there is no unused mud in the pond. Also, the shallowness of the tray allows the soil to breathe more readily, reducing the risk of anaerobic bacteria getting started. A kitty litter tray is good for most situations, but larger trays are certainly acceptable. Care should be taken not to get something that is too large and cumbersome to be moved easily.

When planted in the ground, irises should be provided with plenty of rich loam to grow in. Adding some bone meal to the soil will increase the rate of rootstock division and will give larger and more numerous blossoms in the spring.

As with any Irises, the clumps should be broken apart every couple of years and given fresh soil, especially if they are in containers. In southern California this is best done in the fall and winter months if you want a good bloom during the following spring.

Louisiana Irises are very easy to grow and will provide years of enjoyment if they are given what they want. What they want is shallow water or moist soil and sandy, acidic soil with limited nitrogen. They will thrive in full sun or partial shade. In sunnier locations they tend to bloom a little earlier in the year than they do if they are shaded. In profound shade they may never bloom at all.

Irises will always occupy a special place in water gardens. Their colorful and exotic flowers will always keep people coming back for more. With continued hybridization and experimentation with colchicines, an extract of Crocus bulbs that alters plant genes, and other treatments, the future promises further excitement.

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FAQ - Plants - Louisiana Iris

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