How to plant Irises

Cultivation

Louisiana iris will grow well throughout New Zealand, but are at their best in warm, humid climates where the bearded iris do not fare so well, Sonic Louisiana iris are frost tender but most, if not all, will tolerate light frost and all will grow in cool climates if well mulched in autumn. They are rather adaptable to situation, requiring sun to give the best performance but growing well in filtered sunlight, particularly in hot climates. Probably the most important requirements of Louisiana iris are an acid soil and adequate water in the growing season. Ground preparation is essential to achieve satisfactory results. Louisiana iris like a rich, heavy soil, so large quantities of compost or well rotted animal manure can be incorporated in the soil if it is deficient. Many growers prepare an acid bed, which consists of an area dug out to spade depth lined with plastic sheets with sulphur incorporated into the replaced soil. Louisiana irises grow actively in spring and autumn. I have found a certain degree of summer dormancy but no doubt plants can be kept growing well in summer if adequate water is provided. During the growing period they require a lot of water and for this reason can be grown in standing water or in pots placed in ponds. They are gross feeders and can be heavily composted and fed with well rotted animal manures (be careful of fowl manure as it could be too alkaline), chemical fertilisers suitable for azaleas and camellias or cotton-seed meal. These irises need to be mulched in summer as protection against heat and in winter as protection against frost. Suitable mediums are bark, leaves and acid compost, all of which give protection to the rhizomes, which are inclined to rise toward the surface. For this reason they are best planted 3-5cm below the surface and other planting instructions are similar to those for tall bearded iris. The incorporation of an 8-9 month slow release fertiliser at planting time is recommended. In suitable growing conditions many of the Louisiana iris are rampant growers, needing dividing and replanting after 2—3 years in the ground. This process is best achieved in March or April, although there is an argument for dividing Louisiana iris in November immediately after they have flowered. Good strong plants can be moved throughout most of the year without any harm. Because of their rampant growth Louisiana iris can be invasive so care should be taken to plant them sufficiently far apart to keep them apart. For vigorous varieties 60cm should be allowed.