Optimal Growing Conditions
Once you receive your iris rhizomes, the first step is to un-wrap and rinse the rhizomes, inspect them carefully, then place your rhizomes in a container of water that reaches just to 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. You can add compost and organic matter to acidify alkaline or sandy soils. Add organic material and fertilizer, such as 8-8-8, 13-13-13, Azalea/Camellia fertilizer, or Osmocote to the bed and work into the soil. Organic fertilizers are also effective, although the amounts to use are harder to estimate. Plant your rhizomes with about 1-2 inches of soil over the top of rhizome, and water them in. Mulch also helps hold in moisture while new roots form, and to protect the crowns from freezing in the more northern zones. Ideally, you want to plant them in a triangle about 12 inches apart, to allow for room to increase. 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 to 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. Do not plant under trees whose roots will absorb all the moisture and fertilizer from your irises. With adequate watering, you will see the flowers flourish.
If planting by a water feature such as a pond, you can plant along the water's edge. If planting in the water, make sure the foliage is above the water line or the rhizome will die off.
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 in the fall. You can re-plant them in September or October as well, as this is not long after the new growth period has begun.