LOUISIANA IRIS CULTURE
Louisiana irises are hybrids of native species
found growing in the lower Mississippi River Valley, and in particular, the swamps and
wetlands of Louisiana. Some of these native species, however, have been found in the wild
along the Mississippi as far north as southeastern Missouri and extreme southern Illinois.
Some of the hybrids have been successfully grown as far north as southern Canada, if
mulched well and given protection from drying winds.
In our area, USDA zone 6/5, Louisiana irises bloom,
generally, after the tall bearded irises have finished and before the Japanese irises
start. Usually they bloom about the same time that Siberian irises do, and the combination
can be quite striking. Of course, bloom time is quite dependent on the cultivar. Louisiana
irises require lots of moisture; they are, after all, at home in wet, heavy soils.
SITE AND PLANTING TIME
The preferred planting time is August through
September. If you wait until past the first week of October, the plants may not have
enough time to become established before freezing weather comes and they may heave out of
the ground. Choose a planting location that gets full sun if at all possible. However,
they will survive and bloom with a minimum of a half-day of sun, six to eight hours during
the summer. The site should be one that stays rather moist such as a low spot in the
garden, or beside a pond, lake or running stream. They love to grow in shallow water that
has a depth of one to three inches. They are, after all, native to swamps, but will also
grow well in average garden soil if given plenty of water during dry conditions.
SOIL AND PLANTING
Louisiana irises love soil that has plenty of humus in
it, such as composted manure. They do best in a slightly add soil that has a pH of 6.0 to
6.5, but will also do well within a range of 5.5 to 7.0. Remember that a pH of 7.0 is
considered neutral. Soil may be made more add by the addition of ground sulfur or aluminum
sulfate when preparing the bed. To make the soil less acid, use a little lime. The rhizome
should be planted about two inches deep (not like bearded irises), with the foliage end
pointed away from the center of the clump (if planting more than one of the same variety.)
Do not allow the small roots to become dry before planting. Louisianas are fast spreaders,
so give them plenty of room. Space different varieties at least two feet apart. Water well
after planting and cover with two to three inches of mulch, preferably hard wood or
shredded cypress bark. Do not use leaf mold as mulch; it may contain diseases.
Louisiana irises like lots of moisture. In hot, dry
summer weather they should have a total of between one to two inches of water, either from
rain, or by watering. Be aware that Louisville city water is very alkaline, with a pH of
over 8.5. A good alternative is to collect rainwater, which is very slightly acid, in a
barrel for use when needed.
Louisiana irises are fairly heavy feeders. An
application of a good balanced acid-based fertilizer, such as 8-8-8 or 10-10-10, after the
plants begin active growth in the spring will get them off to a good start. Another
application after blooming is also beneficial. Do not fertilize during the hot "dog
days" of summer.
Divide your clumps after three or four years, or when
the rhizomes from one variety threaten to invade the space of another. If they become
intermingled, they will be very difficult to identify when you divide them.