Society for Louisiana Irises
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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 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
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.
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 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
SLI Site Index
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
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
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
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
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