Growing The Bayou Beauty Louisiana Iris A Swamp Horticultural Treasure

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Deep in the swamps of south Louisiana grows a horticultural treasure that has all the brilliance of precious jewels. Whence this fabulous Louisiana iris came, or when, no one knows.

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It was in the late 1920s that Dr. John K. Small of The New York Botanical Garden first brought these swamp beauties to the attention of the horticultural world. He proclaimed them the most important botanical discovery of the generation.

Note: Louisiana Irises are a taxonomic series of irises (Iris subg. Limniris ser. Hexagonae) and include the species: Iris brevicaulis, Iris fulva, Iris giganticaerulea, Iris hexagona, and Iris nelsonii.

The Ill-Fated Louisiana Iris Area

In the spring of 1925, after completing a collecting trip in Florida, Dr. Small crossed the iris area of Louisiana on his way to the Pacific coast. The bayou banks, marshlands, and roadside ditches were arrayed in splendor. 

At that time, irises grew in magnificent colonies in and around the outskirts of New Orleans. But alas, the improvements and expansion of the great city and the drainage of lowlands and swamp areas over vast regions of the state were rapidly destroying this incomparable natural phenomenon. 

So rapid was this destruction that only a fading memory now remains of many pictorial stands of Louisiana iris most are too young to have ever known.

Near Abbeville, Louisiana, in an isolated area of swampland, grow the so-called giant Abbeville fulvas. Although many initially conceded this to be a distinct species, it was not until 1966 that it was described by the name Iris nelsonii and finally verified as a species in 2003. 

Credit for bringing this iris area to the attention of collectors belongs to W. B. MacMillan of Abbeville, Louisiana, in the late 1930s.

Personal Memories Of The Iris Stands

“I remember well the early morning when I stood on the rim of the swamp, entranced with the picture before me. From waters of inklike blackness rose towering, ageless, cypress trees with branches draped in gossamer gray moss.

The water all around me was pierced with smooth cypress knees of various shapes and heights. Colonies of brilliant-colored iris, on stems 3’ to 5′ feet tall, sparkled above lush green swordlike foliage. They grew so close that care was required in walking among them.

The large flowers were in shades of wine, red, brown, amber, peach, and occasionally old gold and butterscotch tones – the so-called Abbeville yellows. 

In addition, there were flowers of velvety and of smooth texture, flowers of flat form, others with flaring and hanging segments, flowers with sepals showing signal marking in variation, and others with no marking. All had the quill-like style-arm typical of Iris fulva.

“I have another memory of taking a short journey so close to the gulf that the smell of the sea was in the air. A sharp turn in the road brought a gasp of delight over a picture never to be forgotten – blue iris, by the thousands, growing shoulder high on each side of a white shell road as far as the eye could see, with fleecy white clouds sailing on a blue sky above. Walking among the irises, looking into the faces of thousands, finding them all beautiful but with slight color variation, form, signal marking, or height, I felt they must be Iris giganticaerulea in its purest form. Louisiana irises can be grown as a true bog plant or in rich, humus-filled flower borders in gardens where mild weather prevails throughout the winter.”

The Dilemmas Gardeners Face

But what cultural methods must we employ to induce these beautiful swamp irises from the deep south to be happy in dry-land gardens far from their native home? 

How much cold will they tolerate to live and flower profusely live and year after year? What degree of protection, if any, will be required? Ah, those are indeed the million-dollar questions.

Although this iris has undoubtedly grown here for hundreds of years, it is comparatively new to us as a garden plant. Much of the early material written regarding Louisiana irises is of a controversial nature. 

Northern gardeners were thus initially inspired and encouraged to learn by trial and error how to adapt this lovely flowering plant to the existing conditions of their gardens.

Garden Culture

Methods of growing this southern iris successfully in more rigorous climates differ from the natural conditions found in its native habitat. Good drainage would be of supreme importance to ensure the hardiness of the rhizomes.

Deep Soil Preparation

The value of deep soil preparation for planting cannot be overemphasized: this helps provide better winter drainage and an improved reservoir for moisture during the growing period. 

Removing soil to a depth of 12” to 18” inches and refilling the space with a special soil mixture may seem an unnecessarily elaborate procedure. However, the robust and luxuriant growth which will result from this special preparation may mean success.

The Importance Of A Long Season

Many northern gardeners report that the rhizomes are hardy, yet they fail to bloom. It’s likely that the most essential phase of successful cultivation is being ignored: the paramount importance of having the longest possible growth period following the flowering season.

This produces strong foliage growth, which will result in good rhizome development in preparation for flowering the next growing season. This long growing period may be particularly important for successful flowering each year in gardens where winter growth is impossible.

It is quite true that when lacking adequate moisture, Louisiana iris may go completely dormant after blooming and remain so for four or five months with no ill effect on the rhizomes.

Indeed, this occurs during most summers, both in their native swamps and in many gardens. However, over several years, it’s easy to observe that a marked profusion of bloom in the swamps is always preceded by a wet summer.

Good Soil Preparation

In preparing the soil that will induce the growth necessary for flowering these swamp beauties, the coarsest grade of peat moss is the choicest ingredient that can be offered. This could make up 1/3 of the planting medium if you are willing to give them that much. 

They love dairy fertilizer, and making this up to 1/3 of the mix would be to their liking. Any moisture-retentive material, such as unscreened compost or rough wood soil, is desirable as a substitute for dairy fertilizer and peat moss. 

A heavy dusting of cottonseed meal and a well-balanced commercial fertilizer may be used for added richness. Add to all this and thoroughly mix enough loam to form a mound, allowing for future settling and enough elevation to turn surplus winter moisture.

Seasonal Care

In northern gardens, spring planting is recommended. This will permit good establishment and desired foliage growth and rhizome development before the following winter.

As the iris show signs of growth, a program of regular light feedings of a well-balanced commercial fertilizer and copious watering may continue when natural rainfall is lacking until the plants show a natural tendency to go dormant.

Then, in late fall, cut the foliage near the ground and apply mulch. This may be unnecessary, but mulching is generally considered a wise procedure.

Louisiana irises respond so readily to a good culture that the flower size and height of bloom stern are mute evidence of the planting care and attention given during the growing season.

Each state no doubt has a favorite wildflower that reigns supreme in the affection of its people. We of Louisiana marvel at the serene beauty of our treasured Louisiana wild iris in its picturesque setting and hope that gardeners all over the world will soon come to know and love them in their own gardens.