Daniel Gill, Merrill, Thomas A. | 4/19/2005 10:28:55 PM
Called Louisiana irises, they are grown all over the world and have become Louisiana’s floral ambassador to gardeners wherever they are grown. I hope you have some of these wonderful plants growing in your garden.
The species called Louisiana irises are Iris giganticaerulea, I. fulva, I. brevecalulis, I. nelsonii and I. hexagona. Only in Louisiana do all five species occur.
These species are closely related and will cross with one another. Crosses between the species have produced an amazing array of outstandingly beautiful hybrids that also are called Louisiana irises. Most of the Louisiana irises you find for sale will be hybrids of these five species, although the basic species also are beautiful and worthy of use in the garden.
Louisiana irises can be divided and transplanted anytime from August through early October. Unlike most plants, Louisiana irises are at their most dormant stage in the late summer – making now the ideal time to divide them.
You might have noticed how many brown or yellow leaves are on your plants now. Even if you decide you don’t need to divide them this year, it’s a good idea to get in and clean out the unattractive foliage before the new growth starts in earnest. This will make the planting more attractive.
Each year Louisiana irises grow and spread, creating more rhizomes and shoots. Eventually, the plants may become crowded, which can lead to lower vigor and poor flowering. This generally occurs two to three years after the bed is planted, depending on how close they were planted to begin with and how much room they have to spread.
Clumps also may grow beyond their allotted space, and dividing will help keep the clump the size you want and prevent the irises from taking over areas where they were not intended to grow.
The first step in dividing them is to use a shovel or garden fork to lift the Louisiana iris plants from the bed. Try to get as much of the root systems as possible, and do not damage the fans of new growth at the ends of the rhizomes. Put them aside in a shady area, and hose them down to keep them from drying out.
Once the bed is empty, take the opportunity to improve the soil in the bed before you replant the irises. Spread a 2-inch layer of compost or other organic matter over the soil, sprinkle a light application of a general-purpose fertilizer over the area and thoroughly incorporate everything into the bed.
To divide your irises, look over the clumps carefully. You will see that young rhizomes branch off from the older rhizomes. The younger rhizomes have a fan of green leaves at their tips with roots growing out from the rhizome at the base of the leaves. Break or cut off the young rhizomes at the point where they branch off from the old rhizome. Discard the old rhizome and replant the young rhizomes.
Plant the rhizomes horizontally with the fan of foliage facing the direction you want the plant to grow, and carefully cover all of the roots. Space the rhizomes about a foot apart. The top of the rhizome should be just below or barely show above the soil surface. Mulch the bed about 2 inches deep and water thoroughly. If you have any rhizomes left over, pot them to share with friends.
If the weather is dry this fall, winter or spring, water your irises once or twice a week to keep the plants well supplied with water. In addition, an application of fertilizer in February will keep the plants growing vigorously into the blooming season.
Louisiana irises growing in containers in aquatic gardens also may need to be divided and repotted, and this is a good time to do that as well. Remove the plants from the pot, and divide them by following the same procedures as the ones for irises growing in the ground. Use pond fertilizer tablets according to label directions to fertilize your containerized Louisiana irises in aquatic gardens.
This also is a good time to purchase and plant new Louisiana irises into sunny beds or aquatic gardens. Some local nurseries may have them for sale, so it’s worth checking. If you don’t see them available, don’t despair. Blooming plants generally are available in the spring and do just fine planted then as well. Or check out possible mail-order sources online by typing "Louisiana iris" into your favorite search engine.
One other note: There are a few other perennial plants grown in Louisiana gardens that should be transplanted or divided this month. Like the Louisiana irises, they tend to be dormant now and will begin to grow actively sometime in October as the weather cools down.
Feel free to divide and transplant Easter lilies, acanthus and calla lilies. If you’d like to divide or transplant spider lilies (Lycoris radiata, also called hurricane lilies or naked ladies), you may do so as soon as they finish blooming.
Get It Growing is a weekly feature on home lawn and garden topics prepared by experts in the LSU AgCenter. For more information on such topics, contact your parish LSU AgCenter Extension office or visit our Web site at www.lsuagcenter.com. A wide range of publications and a variety of other resources are available.