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Cold temperatures are the most obvious variable factor associated with climate. Two Louisiana species (I. brevicaulis and I. fulva) grow far into the North, and their use in hybridization injects a significant degree of cold hardiness into the offspring. I. giganticaerulea, the tall blue of the Louisiana, Texas, and Mississippi Gulf Coast has been described as a reluctant bloomer in cold climates. However, that may be more due to a shorter bloom season than to cold hardiness.
Reports indicate that Louisianas tolerate frigid temperatures with some protection. Louisiana irises do not die from the cold except in the harshest climates, where the ground freezes hard and the irises are insufficiently protected. Mulch is important as protection, of course, and while snow cover counts as mulch, it cannot be relied upon to be available every year.
A cold climate means a more extended winter and a later bloom season. Louisiana irises that bloom from mid-March through late April along the Gulf Coast may appear from mid-June into July in the cold North. The winter ends later, and the irises have a shorter growing season before the start of the next. Bloom season between the Lower South and the Upper Midwest is staggered by latitude, local conditions, and microclimates.
A shorter growing season means the irises must make the best use of moderate temperatures. While a little shade is fine and beneficial in the South, a full-sun location becomes increasingly important as one moves north. During the shorter growing season, direct sunlight is essential to achieving adequate growth and good bloom.
Even under optimal conditions, the shorter growing season in the North means that bloom stalks may not grow as tall and will have fewer flowering positions compared to more southerly climates. Fertilizing takes on added importance because the irises must be pushed to achieve maximum growth.
Alkaline soil. Growers must amend alkaline soil in some areas. Much misinformation was distributed in years past about Louisiana irises requiring acid soil. They do not, and they thrive in the wild in areas where the soil measures around 7.0 or 7.1. But in West Texas and much of California, for example, the degree of alkalinity must be reined in by adding acid-forming materials or chemicals. Soil modification requires decomposed organic matter, manures, or chemicals such as aluminum sulfate. A soil test is recommended before resorting to chemical alteration of the soil, but organic amendments are an almost universally excellent idea.
If your soil has a clayey composition, rejoice instead of fret. Clay soils should be amended with organic matter to be sure, but clay’s stiffer composition and moisture retention will benefit the irises greatly.
Arid locations such as in the Southwest often have alkaline soil, but the low rainfall additionally presents a major challenge to water-loving plants. Louisiana irises will hardly thrive in a mixed bed of xerophytes or other native plants of the region. In El Paso or Tucson, growers must engage in some form of water gardening.
Insects and Diseases. Every region seems to have its own menagerie of iris pests, but not all bother Louisianas. Sometimes, they are minor nuisances, but gardeners must take action in other cases. Cutworms are reported to damage irises in some areas but not in others. Iris borers are often a menace in cold regions but seemingly no-shows in the hot South. Rust is a problem in Louisiana, but others may escape it. Leaf Miner seems a ubiquitous irritant but not a problem rising to the level requiring poison. Growers should investigate the experiences of others with nematodes, grasshoppers, snails and slugs, and verbena bud moths. Each has its own unique prevalence and antidotes, but most will not be a serious problem.
The best cultural advice seems to be to contact iris organizations and growers in your area to find the problems and solutions to which you should pay attention.
Several cultural options for growing Louisiana irises are evident from their attributes. In some areas, they are a matter of choice, but climate or other considerations may dictate approaches in others.
Undoubtedly, most gardeners grow Louisiana irises in mixed beds alongside other ornamental plants. The irises are among many choices on the pallet of plants used to create beautiful landscapes. Louisianas have a great deal to offer in this setting. The texture of iris foliage provides a welcome contrast to finer and less linear plants. With proper culture, iris foliage in temperate climates remains green and growing through the winter when other plants often go dormant. It may be a challenge to meet the irises’ optimal water needs in a bed alongside plants that prefer drier conditions, but for good iris bloom and attractive summer foliage, extra moisture is essential. As long as the irises get at least a half day of sun, sufficient water and fertilizer are applied, and tree roots do not out-compete them, Louisiana irises are great additions to a mixed bed.
Mixed beds require choices of both the iris cultivars and companion plants. The best companion plants for a given area vary too much to risk specific suggestions. Those choices are almost entirely local and personal. The selection of Louisiana iris cultivars depends on personal preference, growth habit, and the desired role in a planting. Most cultivars are relatively tall, blooming 34-38 inches, so placement at the front of a bed may not be a good choice. But low-growing varieties are available, none more common than the dark purple ‘Black Gamecock’, which is probably the most widely-grown Louisiana iris cultivar nationwide. Coming from an I. brevicaulis background, the iris is not only short but also cold hardy. While Louisiana iris cultivars generally perform well, some may do better in particular areas, so it pays to investigate which cultivars are popular in your region.
Another approach is to cater to the irises’ love of water. This can take several forms. If you have a pond, plant the irises near the shallow edges. They will form dense clumps and require relatively little care. This approach is as close to their natural condition as any cultural practices available. Rhizomes planted near the pond’s edge, preferably just above the water line, will grow into the shallow water and find the depth they prefer. Ponds with a steep dropoff to deep water will not work. The irises prefer an inch or two depth, and some will happily find their way to six inches. Irises planted at pond’s edge can be fertilized but may not require it.
Planting bare root rhizomes directly into the water is not advised. Even though they are water-loving plants, Louisiana irises can rot if placed in water when their root system is not established. They also can float off if not yet anchored. Deep water should avoided because the irises must be able to maintain most of their foliage above water. Ponds with a highly varying depth may not work well.
Louisiana irises can be planted in containers and sunk into artificial ponds, or planted directly in soil if the pond has a dirt bottom. Irises in containers in water should be fertilized with spikes or other fertilizers designed for ponds.
In water, the irises can grow especially vigorously, and the length of rhizomes increases with each new leaf. Wide pots are required to contain the irises, which must be replanted more often than in a garden bed. The length of a rhizome varies greatly by variety, and experimentation may be required to find the varieties most compatible with pond culture. At the extreme, I. giganticaerulea rhizomes will grow up to a foot long in a swamp, and offsets in each direction would not last long in a pot. While an extreme case, it illustrates the importance of searching for cultivars that produce smaller rhizomes.
A more manageable way to engage in water culture is to plant in beds lined with plastic or in tubs without drain holes or with holes only near the rim. This approach creates bog-like conditions on a limited basis. Lined beds can be as long and wide as you wish. Tubs essentially are individualized bogs with, usually, one variety planted in each. With any approach involving water culture, expect the irises to grow larger and more vigorously. If you wish to maintain the identities of species or cultivars, plant farther apart to minimize mixing.
One popular approach is to plant in mortar mixing tubs 6″ or 8″ deep that can be purchased in the construction section of “big box” stores. As long as they are adequately watered, the boggy conditions in the tubs are much to the irises’ liking. Like a clay pot, however, the tubs will dry out if the water is not replenished. Unlike irises in mixed beds, they cannot draw up groundwater by osmosis. Tubs lacking drain holes will stay boggy for a while, but they can get bone dry without rain or irrigation. Sink tubs in the ground or disguise them with a border and mulch to take on the look of a mixed flower bed. Such tubs are an excellent way to combat tree roots that otherwise would drink much of the water intended for irises. Placement of irises nearer trees is possible if the irises are in tubs.
Lined beds offer an advantage over smaller tubs. Because of their size, keeping them wet is easier. Lined beds can be sunken to ground level or placed above ground using wooden sides.
Louisiana irises will grow well in pots with drain holes if sufficiently deep and wide. Rhizome growth will not be as rampant as in water culture, but you must keep the pots consistently watered and watch for rhizomes creeping over the edges. A good strategy is to set the pot in a shallow, non-draining tray that holds an inch or two of water, which the plants can draw up as needed.
In the Upper Midwest or West, water culture is generally not advisable. Mulch or other practical protection may be insufficient to prevent containers, lined beds, and tubs from freezing like an ice cube. In-ground plantings with heavy winter mulch have proven very successful, however..
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