Most gardeners think of cultivation of Louisiana irises in terms (If moving them to an upland garden bed somewhere around the home site. They may be used, however, around the borders of a pond or stream where they will require practically no attention other than hand weeding provided the water maintains a fairly constant level throughout the year.
Louisiana irises are native of some of the most fertile land in the world, the alluvial deposits of the Lower Mississippi Valley. In addition, they are found growing in water. When they are moved to an upland garden the grower should provide, as nearly as possible, cultural conditions which approximate the natural environment of the plants.
The first consideration is a fertile soil, high in both organic matter and plant food. This is best supplied by animal manure where such is available. For town and city gardeners the problem of purchasing farm manures is very great. Much of the material offered is badly leached, contains a high percentage (If dirt and is full of noxious weeds and grass. Most seed and fertilizer stores now offer powdered, sterilized manure from the stock yards for sale" in 50-pound bags. This is expensive,but very satisfactory. The best substitute for manure is completely decomposed leaf compost and probably the next best source of organic matter is peat moss, supplemented with a complete mineral fertilizer. Most of the alluvial soils heed only nitrogen as a supplementary plant food. Soils which are high dn sand and the upland soils, as a rule, also need phosphoric acid and potash. To take care of any possible deficiency it is well to work into the soil before planting a complete fertilizer, such as an 8-8-8, using B to 10 pounds per 100 square feet of bed.
Propagation is by seed or from planting rhizomes. While the latter may be moved at any time of the year, provided watering is done frequently, the best season for transplanting is during the period of August through October. At this season the plants are partially dormant and transplanting may be done without danger of loss. The rhizomes should be planted shallow, with the top of the rhizome just below the surface of the ground, and the newly planted bed should be kept well watered until the beginning of fall rains. It is advisable -to- mulch the bed about two inches deep after planting. Suitable mulching materials are bagasse, rotten sawdust, rice hulls, partially decomposed leaves, peat moss and even pine straw. The mulch tends to conserve moisture and helps retard the growth of annual weeds and grass. In northern climes a much heavier mulch is needed to protect the rhizomes from the severe cold.
During the spring and early summer growing and blooming periods the iris plants should never be allowed to suffer for water. The garden hose should be used frequently and generously during periods of drought.
Most losses in beds of Louisiana irises occur during the months of July through September. The foliage dies down in early July, leaving the rhizomes exposed to the heat of the summer sun. If the rhizomes are not protected by renewing the mulch, by a light shade, or by covering lightly with light, loamy soil, they dry up and eventually rot. The only rot which has ever been observed in Louisiana iris rhizomes by the writer is that which always follows over-exposure to the summer sun. If mulching material for renewing the mulch is not available in early July all of the dead foliage and the old bloom stalks should be cut to the ground and the bed should be covered lightly with light sandy loam soil. The bed may be planted to summer annuals which will provide both shade and beauty. One of the most satisfactory of these is Crotalaria retusa, which is commonly called Japanese sweet pea.
In the Lower Gulf Coast Region the seed pods mature around the first of July. These should be harvested, shelled and the seed planted just as the pods begin to turn yellow. The seed may be planted in a bed in the ground immediately after harvest. If the bed is kept shaded and moist the seed will germinate in October. If planting is delayed for several months the seed may not germinate until the following year. In regions where the winters are severe the seed may be planted in gallon cans in which holes have been punched for drainage. A board may be placed over the top of the can for protection from mice. During periods of extreme cold the little seedlings may then be brought indoors. The seedlings may be set out in rows early the following spring and cultivated with a hoe during the summer growing season. The following year they should bloom.
As the rhizomes increase and become too thick in the planting, the bed should be reworked and the rhizomes reset. This need not be done annually, hut each fall or winter the bed should be fertilized and the mulch renewed.
To summarize: cultivation consists of a fertile, well prepared bed; a good mulch to conserve moisture and protect the rhizomes; hand weeding as needed; and frequent watering during periods of hot, dry weather. Where these things are done conscientiously, Louisiana irises are as much at home in an upland garden as in their native bogs.