Add beautiful Louisiana irises to your garden

Richard Bogren, Gill, Daniel J.  |  3/30/2009 8:21:31 PM

For Release On Or After 04/03/09

By Dan Gill
LSU AgCenter Horticulturist

Among my favorite spring wildflowers are the amazingly beautiful native Louisiana irises. In gardens and landscapes, hybrids of our native species bloom in a rainbow of colors with large, showy flowers on tall stems. Their extraordinary beauty and reliability in the garden have made Louisiana irises increasingly popular all over the world, but they still deserve more recognition and use here in their home territory.

Though a number of iris species are native to Louisiana, only five species, Iris brevicaulis, Iris fulva, Iris giganticaerulea, Iris hexagona and Iris nelsonii are known as “The Louisianans.” Although I. brevicaulis and I. fulva are native to the Mississippi Valley from Louisiana to Ohio and I. giganticaerulea and I. hexagona are found along the Gulf Coast from Mississippi to Texas, only in south Louisiana do all five species occur together. Once vast native stands of these irises thrived, particularly in the area that is now New Orleans.

These five species are closely related and will interbreed with each other but with no other species. The crossing, or interbreeding, of these species has resulted in the modern hybrid varieties we grow today. Their large, attractive flowers cover a broad range of colors that include many shades of blue, purple, red, yellow, pink, gold, brown, lavender, burgundy and white. Varieties with bicolor flowers of contrasting colors, bright yellow signal markings or ruffled petals add to their beauty.

The best time to plant Louisiana irises is in August and September when they are most dormant, but you can buy them now at local nurseries and plant them while they are in bloom. That way you can pick out the colors and types of flowers you like best. When purchased and planted now, however, Louisiana irises must be handled carefully to avoid damaging the foliage and flower buds. And they may need to be staked after planting.

In their native habitats, the original species often grow in swampy or boggy conditions, so Louisiana irises make outstanding additions to aquatic gardens. But they also can be grown in ordinary garden beds with excellent results. Their culture is really quite easy.

Louisiana irises should be grown with as much direct sun as possible. Although they will tolerate shade for part of the day, at least six hours of direct sun is needed for good blooming. Avoid locating beds near large trees that create shade and have extensive root systems that would compete with the irises.

When preparing a spot to plant Louisiana irises, incorporate a generous 3-inch layer of compost, rotted manure or peat moss and some general-purpose fertilizer. The plants do best in a soil high in fertility and organic matter.

Plant Louisiana irises in beds at the same level they were growing in the container they came in. The rhizome should be at the soil surface and covered with a couple of inches of mulch. If you are planting several plants in a group, space them about 12 inches apart.

Care must be taken to protect the foliage and flower stalks when planting irises from a container this time of year. Brace them carefully when bringing them home to keep them from falling over and damaging the flowers and buds. They may be top-heavy and unstable when first planted. If necessary, place a stake next to the plant and loosely tie the plant to it. Established plants generally do not need to be staked.

Aquatic culture is one of the easiest and most natural ways to grow these irises – and the foliage tends to stay more attractive through the summer. Simply place a potted iris into your pond or aquatic garden so that the rim of the pot is a few inches below the water’s surface. Every one to two years divide and repot them in heavy garden soil.

Providing adequate moisture is an important part of growing Louisiana irises. Keep newly planted irises well watered, and continue to water during dry weather until late June. After that, as the irises go dormant, watering is less important unless you’re trying to keep the foliage attractive. Resume watering in late September as the plants come out of summer dormancy.

General care of established Louisiana irises is easy. Fertilize your irises in October and February. Irises growing in containers in aquatic gardens should be fertilized by lifting the pot out of the water and placing aquatic fertilizer tablets below the soil surface.

Always keep iris beds mulched. This is an essential part of good culture, especially in the summer. A 2- to 3-inch layer of leaves, pine straw or other mulching materials helps prevent sunscald of the rhizomes as well as reduce weeds and maintain soil moisture.

The large seedpods that form after flowering should be removed as soon as you notice them to keep the plants more attractive and vigorous. Trim back unattractive foliage in mid- to late summer.

Give these delightful native plants a spot in your garden, and you’ll appreciate their beauty, reliability and easy care for a long time.


Rick Bogren

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