Optimal Growing Conditions
The first step is to place your rhizomes in water that reaches the bottom of the foliage. You will need to keep them there until you're ready to plant them. They can be stored this way for up to a month, but take care not to let them dry out, or you'll risk the plants going into dormancy.
When you're planting irises, you want to make sure the soil has a pH of 6.5 or lower. Plant them with about 1-2 inches of soil over the rhizome, and then add compost and organic matter to acidify alkaline or sandy soils. Mulch also helps hold in moisture while new roots form. Ideally, you want to plant them in a triangle about 12 inches apart, to allow for room to spread. The rhizome will grow in the direction the fans are facing, and will also put out new shoots on either side of the mother rhizome.
If possible, prepare beds a few weeks before planting. Louisiana Irises thrive when growing in half or full sun, so choose your planting location carefully. If you're growing them in full sun, you need to water deeply once a week, especially during dry periods. With adequate watering, you will notice the flowers flourish.
The Louisiana Iris's growth cycle begins in the fall and continues through winter, culminating in a burst of rapid growth in the spring. That means the best time to plant and divide them is mid-to-late August. You can plant them in September or October as well, as this is not long after the new growth period has begun.