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Society for Louisiana Irises

Webmaster's Note: The author, Robert Turley is the Calcasieu Parish Extension Horticulturist in Lake Charles, Louisiana. Some information in this article is more applicable to Louisiana or similar warm, moist climates.
LOUISIANA IRIS........."Les Gles de Marais"

The Louisiana iris continues to be a popular plant for Louisiana landscapes. Les gles de marais, is the name they were called by the early French settlers who found them growing abundantly in the marshes of south Louisiana. This native iris of Louisiana is also the official State wildflower.
Louisiana irises need not be grown in water or under bog conditions, however, don't overlook this important use of the native iris. Water gardening has become very popular in the last decade and Louisiana Iris are a natural in this setting; however, for decades they have been grown under ordinary garden culture with excellent results. The native iris through the work of backyard hybridizers and a few nurserymen, have transformed this simple wild flower into Belles of a Mardi Gras Ball. The culture is very easy, provided a few simple rules are followed. The conditions described are for Louisiana
General Location
Louisiana irises should be grown in as full sun as possible, but under no circumstances should they get less than a half day of sunlight. The irises will not bloom properly in dense of full shade. Also, the irises should not be grown in competition with large trees or plants with extensive root systems that would use most of the soil moisture. Two types of garden locations can be considered: beds containing only Louisiana irises, or beds containing Louisiana irises mixed with other plants. Louisiana irises can be mixed with most of the smaller ornamental plants, subject only to the limitations of acid soil and extensive watering needed when drought occurs during the growing season.
Soil Conditions and Preparation
An acid soil is a must for Louisiana irises; soil pH of about 6.5 or lower is best. Any soil suitable for azaleas and camellias is ideal. Irises also need a soil high in fertility and organic matter. Add sphagnum peat, compost leaves or rotted manure if necessary. If the soil has a clay texture, adding some sand may help. Prepare the beds a few weeks before planting the irises if they are to be planted in new beds. Work the soil, preferably with a power tiller. Add the organic material and a generous amount of commercial fertilizer (8-10 lbs. per 100 sq. feet of a complete fertilizer such as 8-8-8 or 8-24-24) and work in.
Planting and Dividing
The best time to plant and divide Louisiana irises is mid-to-late August and September. Transplanting immediately after blooming is not recommended. If existing beds are to be divided and replanted, dig out all the irises and rework the beds, adding organic materials and a commercial fertilizer as described for new beds. Replant as soon as possible, preferably the same day. Do not allow the newly planted beds to dry out; water every few days until the plants are established. Planted in a triangular format (about 12 inches apart), they can be left 3 to 4 years and will form nice clumps.

Irises grow in the direction they face; at least two offsets generally form each year, one on each side of the rhizome. Each rhizome blooms only once, then the offsets bloom the next year. Good growth and offset formation are, therefore, necessary each season for consistent bloom. The offsets represent vegetative reproduction and are identical in every respect to the parent rhizome.
Watering
Watering is often necessary to achieve a sufficient growing season for good bloom. Our growing season is about eight to ten months from north to south in the state. Once new growth has begun, the beds should not be allowed to dry out. September and October are generally quite dry in Louisiana, and it is important to give the iris beds a thorough soaking at least once weekly during such dry periods. Modify the watering schedule according to growth.
Fertilizing
For new or replanted beds (to which commercial 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 application at the start of the growing season (with good watering in), and then the light dressing just before bloom. Complete fertilizers such as 8-8-8 are preferable to high nitrogen fertilizers. High nitrogen can cause the plants to produce leafy growth while suppressing flowering; it can also make the plants more susceptible to disease.
Mulching
Mulching is an essential part of good culture. Mulches serve many purposes, such as maintaining soil moisture and keeping weeds under control. But mulching during the summer dormant period serves one essential function which cannot be met by any other means, except planting the irises in water.

The rhizomes lie on or very near the surface; the hot summer sun on the rhizomes (after the foliage has died back) will cause a condition known as sunscald. This causes the rhizome to deteriorate and rot. The tip of the rhizome will continue to grow, but it is almost a certainty that no blooms will be obtained the next season. This is one of the main reasons for failure of Louisiana irises to bloom consistently.

The problem is easily solved by applying a mulch. About 2-3 inches of rotted or even semi-rotted leaves, bagasse (sugar cane fiber) or pine straw are excellent mulches. As little as one-half to one inch of soil can also be used if nothing else is available. But by all means protect the rhizomes from the sun during the dormant period. Keeping a mulch on the irises the entire year is best, and it is a necessity in colder areas.

Pests and Disease
Fortunately, Louisiana irises are not prone to many diseases and insect pests. The most common problems are:

Rust shows up 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. Since rust is a fungus disease, spraying with fungicides may help, but it is difficult to control. Avoiding too much fertilizer, especially high nitrogen, may limit the spread. Leaf Miner shows up as white steaks along the leaves, particularly near the base of the leaves in hot weather. The outermost leaves may collapse. A systemic insecticide is most effective if applied in early fall. Systemic insecticides are poisonous and must be used with care.

Cutworms may be a problem early in the growing season as the new growth is starting. These chewing insects will "cut down" the plant at the base. A fertilizer fortified with an insecticide, such as that sold for control of lawn chinch bugs, is quite effective against cutworms.

Southern Blight, caused by a fungus in the soil, may occur under warm, moist conditions. A single rhizome or patch of rhizomes may be affected and may rot before the problem is detected. If it is a severe infection, it may be necessary to move the irises to another location temporarily and wash the rhizomes with dilute 10% chlorox. Soil fungicides such as "terraclor" may be applied without moving the plants. But if the infection is severe, the plants may have to be dug and moved. Treat the soil in the new area with "terraclor" (4 ounces per 100 square feet) and mix it into the soil before replanting.

Snails and slugs may climb up the scapes and disfigure the blooms, particularly under conditions of high humidity and rainfall. Snail and slug baits are sold under several trade names and are effective when used according to the label.

Sun scaldis not a disease, but a condition resulting from the sun scorching the rhizomes in midsummer. It has been discussed under culture, and mulching in summer is 100% effective in controlling this problem.

Interesting to note that Louisiana Iris when grown in bog or water garden conditions have none of these maladies!

Orchard orioles may cause problems in certain areas near their migratory routes. They tear up the blooms when they seek the nectar. There is no effective way to stop them. Cut the scapes and take them inside if you want to enjoy them.

___________________
This garden information is provided by Robert M. Turley, Calcasieu Parish Extension Horticulturist, 7101 Gulf Hwy., Lake Charles, LA 70607-7414

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*Society for Louisiana Irises* *Main Sections* Home About SLI Awards & People Culture & Cutivars Introduction Culture More Culture #1 More Culture #2 Hybridizing I. nelsonii Rebloomers Registry '03 Registry '02 Registry '01 Registry '00 Registry '99 Registry '98 Registry '97 Registry '96 Registry '95 Registry '94 Registry '93 Directory & Links Convention & Events Lairis List Serv Publications	*Society for Louisiana Irises* Webmaster's Note: The author, Robert Turley is the Calcasieu Parish Extension Horticulturist in Lake Charles, Louisiana. Some information in this article is more applicable to Louisiana or similar warm, moist climates. LOUISIANA IRIS........."Les Gles de Marais" The Louisiana iris continues to be a popular plant for Louisiana landscapes. Les gles de marais, is the name they were called by the early French settlers who found them growing abundantly in the marshes of south Louisiana. This native iris of Louisiana is also the official State wildflower. Louisiana irises need not be grown in water or under bog conditions, however, don't overlook this important use of the native iris. Water gardening has become very popular in the last decade and Louisiana Iris are a natural in this setting; however, for decades they have been grown under ordinary garden culture with excellent results. The native iris through the work of backyard hybridizers and a few nurserymen, have transformed this simple wild flower into Belles of a Mardi Gras Ball. The culture is very easy, provided a few simple rules are followed. The conditions described are for Louisiana General Location Louisiana irises should be grown in as full sun as possible, but under no circumstances should they get less than a half day of sunlight. The irises will not bloom properly in dense of full shade. Also, the irises should not be grown in competition with large trees or plants with extensive root systems that would use most of the soil moisture. Two types of garden locations can be considered: beds containing only Louisiana irises, or beds containing Louisiana irises mixed with other plants. Louisiana irises can be mixed with most of the smaller ornamental plants, subject only to the limitations of acid soil and extensive watering needed when drought occurs during the growing season. Soil Conditions and Preparation An acid soil is a must for Louisiana irises; soil pH of about 6.5 or lower is best. Any soil suitable for azaleas and camellias is ideal. Irises also need a soil high in fertility and organic matter. Add sphagnum peat, compost leaves or rotted manure if necessary. If the soil has a clay texture, adding some sand may help. Prepare the beds a few weeks before planting the irises if they are to be planted in new beds. Work the soil, preferably with a power tiller. Add the organic material and a generous amount of commercial fertilizer (8-10 lbs. per 100 sq. feet of a complete fertilizer such as 8-8-8 or 8-24-24) and work in. Planting and Dividing The best time to plant and divide Louisiana irises is mid-to-late August and September. Transplanting immediately after blooming is not recommended. If existing beds are to be divided and replanted, dig out all the irises and rework the beds, adding organic materials and a commercial fertilizer as described for new beds. Replant as soon as possible, preferably the same day. Do not allow the newly planted beds to dry out; water every few days until the plants are established. Planted in a triangular format (about 12 inches apart), they can be left 3 to 4 years and will form nice clumps. Irises grow in the direction they face; at least two offsets generally form each year, one on each side of the rhizome. Each rhizome blooms only once, then the offsets bloom the next year. Good growth and offset formation are, therefore, necessary each season for consistent bloom. The offsets represent vegetative reproduction and are identical in every respect to the parent rhizome. Watering Watering is often necessary to achieve a sufficient growing season for good bloom. Our growing season is about eight to ten months from north to south in the state. Once new growth has begun, the beds should not be allowed to dry out. September and October are generally quite dry in Louisiana, and it is important to give the iris beds a thorough soaking at least once weekly during such dry periods. Modify the watering schedule according to growth. Fertilizing For new or replanted beds (to which commercial 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 application at the start of the growing season (with good watering in), and then the light dressing just before bloom. Complete fertilizers such as 8-8-8 are preferable to high nitrogen fertilizers. High nitrogen can cause the plants to produce leafy growth while suppressing flowering; it can also make the plants more susceptible to disease. Mulching Mulching is an essential part of good culture. Mulches serve many purposes, such as maintaining soil moisture and keeping weeds under control. But mulching during the summer dormant period serves one essential function which cannot be met by any other means, except planting the irises in water. The rhizomes lie on or very near the surface; the hot summer sun on the rhizomes (after the foliage has died back) will cause a condition known as *sunscald. This causes the rhizome to deteriorate and rot. The tip of the rhizome will continue to grow, but it is almost a certainty that no blooms will be obtained the next season. This is one of the main reasons for failure of Louisiana irises to bloom consistently. The problem is easily solved by applying a mulch. About 2-3 inches of rotted or even semi-rotted leaves, bagasse (sugar cane fiber) or pine straw are excellent mulches. As little as one-half to one inch of soil can also be used if nothing else is available. But by all means protect the rhizomes from the sun during the dormant period. Keeping a mulch on the irises the entire year is best, and it is a necessity in colder areas. Pests and Disease* Fortunately, Louisiana irises are not prone to many diseases and insect pests. The most common problems are: Rust shows up 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. Since rust is a fungus disease, spraying with fungicides may help, but it is difficult to control. Avoiding too much fertilizer, especially high nitrogen, may limit the spread. Leaf Miner shows up as white steaks along the leaves, particularly near the base of the leaves in hot weather. The outermost leaves may collapse. A systemic insecticide is most effective if applied in early fall. Systemic insecticides are poisonous and must be used with care. Cutworms may be a problem early in the growing season as the new growth is starting. These chewing insects will "cut down" the plant at the base. A fertilizer fortified with an insecticide, such as that sold for control of lawn chinch bugs, is quite effective against cutworms. Southern Blight, caused by a fungus in the soil, may occur under warm, moist conditions. A single rhizome or patch of rhizomes may be affected and may rot before the problem is detected. If it is a severe infection, it may be necessary to move the irises to another location temporarily and wash the rhizomes with dilute 10% chlorox. Soil fungicides such as "terraclor" may be applied without moving the plants. But if the infection is severe, the plants may have to be dug and moved. Treat the soil in the new area with "terraclor" (4 ounces per 100 square feet) and mix it into the soil before replanting. Snails and slugs may climb up the scapes and disfigure the blooms, particularly under conditions of high humidity and rainfall. Snail and slug baits are sold under several trade names and are effective when used according to the label. Sun scaldis not a disease, but a condition resulting from the sun scorching the rhizomes in midsummer. It has been discussed under culture, and mulching in summer is 100% effective in controlling this problem. Interesting to note that Louisiana Iris when grown in bog or water garden conditions have none of these maladies! Orchard orioles may cause problems in certain areas near their migratory routes. They tear up the blooms when they seek the nectar. There is no effective way to stop them. Cut the scapes and take them inside if you want to enjoy them. ___________________ This garden information is provided by Robert M. Turley, Calcasieu Parish Extension Horticulturist, 7101 Gulf Hwy., Lake Charles, LA 70607-7414 SLI Site Index