Society for Louisiana Irises
The Culture of Louisiana Irises
Note: Most of the following data is taken from the book The Louisiana Iris: The Taming of a Native American Wildflower, second edition, Marie Caillet, et al., editors, 2000, pp. 145-163. This book, which was published by the Society for Louisiana Irises, can be purchased from the Society. For more information on purchasing The Louisiana Iris: The Taming of a Native American Wildflower
Growing Louisiana Irises
Louisiana irises grow well in much of the world, proving highly adaptable as to climates, soils, and cultural practices. Despite the common perception that Louisiana irises must be grown in bogs or water gardens, they will tolerate a wide range of moisture conditions. While they will usually survive a periodic drying out, they will not prosper nor bloom well if grown with less than an inch of water per week during the growing season.
Like most irises, Louisianas need sunlight in order to prosper. They bloom best with six to eight hours of sunlight per day. In hot climates, and in the desert southwest, afternoon shade would be good. If you have a low area in your garden where water stands for long periods, you probably have a good place to grow Louisiana irises—assuming you have adequate sunlight.
Louisiana irises tolerate a wide range of soil types and acidity levels. The old belief that these irises preferred a highly acidic soil has been disproved. The best advice is to avoid both pH extremes.
Louisiana irises evolved in the lowlands of the southern Mississippi delta, and thus they tolerate heavy clay soils. Indeed, clay soils retain moisture over a long period, which Louisianas love. These irises will also grow well in a soil with high organic matter content, as long as it is moist; they suffer considerably when growing in sandy soils unless copious amounts of organic matter are added.
Louisiana irises grow quite well in beds that have been lined with plastic. Such beds should be at least six inches deep.
While Louisiana irises will tolerate moderately dry conditions for short periods of time, they should never be allowed to dry out completely. Upon being planted, young rhizomes need to be kept constantly moist for at least one week. Once established they will grow and bloom in a normal perennial bed or border. These irises respond well to deep watering rather than a mere “sprinkling.” Drip irrigation can be very effective.
Louisiana irises will always produce best if given lots of water. They will even grow and bloom in standing water. They are ideal for growing in pots sunken into fishponds.
Obviously, irises growing in standing water will need more attention to feeding than ones planted in soil. The standing water can dissolve nutrients quickly, requiring more frequent feedings.
Given their preference for even moisture, Louisiana irises respond well to being mulched. Mulching has the added advantage of regulating fluctuations in soil temperature, and it also protects the rhizomes (which often grow right at the top of the soil line) from the dreaded sunscald and the extreme temperatures. Importantly, good mulch will deter weeds from invading your growing area.
Many long time growers of Louisiana irises use pine needles (known as “pine straw”) to mulch their beds. They are long lasting and do not mat down. Leaf mold makes great mulch. Avoid mulches of heavy woody material as it might take nitrogen from you soil during the decomposition process. Be forewarned that hay might make good mulch, but it usually contains weed seeds.
In hot climates Louisiana irises rhizomes are subject to sunscald, a common problem which can result in poor bloom, rot, and other afflictions.
Planting and Transplanting
The number one rule in planting or transplanting Louisiana irises is to prevent their drying out. (The number one rule in acquiring Louisiana irises is to purchase them from reputable dealers.) Plants are normally shipped in the early autumn because that is when the plants are coming out of their summer doldrums and getting ready to spurt into growth. That does not mean you are limited to planting Louisianas to the autumn. Potted specimens, of course, can be planted at any time during the growing season. In warmer climes these tough irises can be planted at just about any time, assuming you provide protection from the hot sun and adequate water. In colder regions of North America they should be planted early enough in the autumn so the roots can get established before the onset of cold weather.
Gardeners new to growing Louisiana irises often plant them too close together. These irises grow rapidly, producing long rhizomes that often cover eight inches or longer in one growing season. Most experienced growers space clumps at least two feet apart, but more is preferable.
Every few years Louisiana iris growers usually transplant or thin their plantings. Some cultivars increase very rapidly, while others might be quite slow. Upon lifting a group of Louisiana irises one often notices that new plants have developed all along the sides of the rhizomes. Each of these offsets is a new rhizome and will develop into a mature plant if given sun, nutrients, and water.
When planting Louisiana irises in water settings a few special precautions might be advisable. For example, when planting rhizomes in a pot for sinking in a pond, it is good to pin the rhizomes into the soil using a bent metal rod. That will prevent the rhizomes from floating out of the soil, or keep fish from pulling up the new plants. Since you can expect rampant growth and increase when Louisiana irises are grown in submerged pots, plant fewer than normal rhizomes per pot. When selecting a pot for submerging under water, choose one that is relatively shallow but quite wide. Potted specimens, especially when grown in water, require regular feeding during the growing season as nutrients leach out easily.
Experts disagree as to exactly what water depth is best for submerged specimens, but maximum increase seems to occur when the water is only one inch above the rhizomes. Many gardeners prefer to plant the rhizomes at the edge of a pond and allow the rhizomes to seek their own preferred level of submersion.
If you have not grown Louisiana irises previously, you might be surprised at what heavy feeders they are! To produce at their full potential, these irises should be fed on a regular schedule (and, of course, watered and mulched nicely).
Most growers feed their Louisianas twice each year, a heavy application of a balanced fertilizer (such as a 13-13-13 blend) in the early spring, with a lighter booster feeding in the autumn--which should include more phosphorus and less nitrogen (such as a 5-20-10, or a 10-20-10 ratio). You can also use water-soluble fertilizers to give a little “boost” if needed.
Use an acidifying fertilizer, such as those marketed for azaleas and camellias, if you are gardening on alkaline soils. These granular fertilizers should be applied a few inches from the iris rhizomes, and then lightly tilled-in. Newly planted rhizomes should not be fed until new growth has begun.
Of course, Louisiana irises respond very well to “organic” fertilizers as well as those made synthetically. A natural acidifying fertilizer for Louisiana irises might contain cottonseed meal, alfalfa pellets, or rotted pine needles. Organic fertilizers sometimes require digging into the soil to be effective.
Applying fertilizer to Louisiana irises, which are growing in a pond, requires a bit more advice. If you have fish in your pond, the fertilizer should be applied as “stakes” that are pushed below the soil line.
© 2000 SLI All rights reserved.
© 2000 SLI All rights reserved.