A guide to Louisiana irises: How, where and when to plant these beautiful native flowers (2024)

Among my favorite spring wildflowers are the amazingly beautiful native Louisiana iris species. You may see them blooming in swampy or boggy areas or in ditches along roads.

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 ease of care have made Louisiana irises increasingly popular all over the world, but they still deserve more recognition and use here in their home territory.

Louisiana irises fit in well with the growing trend toward more use of native plants. I try to encourage this trend whenever possible, and it's easy to recommend this reliable, native flowering perennial for our garden beds.

Five species, Iris brevicaulis, Iris fulva, Iris giganticaerulea, Iris hexagona and Iris nelsonii are known as the Louisiana irises. Although I. brevicaulis and I. fulva are native to the Mississippi valley from Louisiana to Ohio, I. hexagona is native from the southern East Coast to Texas, and I. giganticaerulea is found along the Gulf Coast from Mississippi to Texas. But only in south Louisiana do all five species occur together, and I. nelsonii is only found in south Louisiana.

There were once vast native stands of these irises in Louisiana, particularly in the area now covered by New Orleans.

These five iris species will readily interbreed. The crossing, or interbreeding, of these species has resulted in the modern Louisiana iris hybrid cultivars we grow today. Their large attractive flowers cover a broad range of colors, including many shades of blue, purple, red, yellow, pink, gold, brown, lavender, burgundy and white. Cultivars 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 dormant, but you can plant them now while they are in bloom and pick out colors and types of flowers you like best. When planted now, however, Louisiana irises need to be handled carefully to avoid damaging the foliage and flower buds.

Although in their native habitats the original species often grow in swamp or bog conditions -- and Louisiana irises make outstanding additions to aquatic gardens -- they also can be grown in ordinary garden beds with excellent results. Their culture is really quite easy as long as you provide the right growing conditions and are familiar with their seasons of growth and dormancy.

Louisiana irises should be grown with as much direct sun as possible. Although they will tolerate shade for part of the day, at least about six hours of direct sun is needed for good blooming. Avoid locating beds near large evergreen trees that create shade and 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 a general purpose fertilizer following label directions. The plants prefer a soil high in fertility and organic matter. They also generally prefer an acid soil, though here in New Orleans where our soils are slightly alkaline they do very well.

Aquatic culture is one of the easiest and most natural ways to grow these irises, and the foliage tends to stay more attractive in the summer. Simply place your potted iris into your decorative 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. You also can simply plant them into the soil at the edge of a pond, and they will grow along the edge and down into the shallow water.

Plant Louisiana irises in beds at the same level they were growing in the container. The rhizome should be at the soil surface. Care must be taken to protect the foliage and flower stalks when planting irises from a container at this time of year. They may be top heavy and unstable when first planted, but do not allow the foliage or bloom spikes to flop over or break. If necessary, place a stake next to the plant and loosely tie it up. Established plants generally do not need to be staked.

The farther apart the irises are planted, the longer they may be left without dividing. If the plants become too crowded, they will not bloom as well. Crowding and insufficient sun are common reasons for poor bloom. If you're planting several plants in a bed, plant them in a group spacing them about 12 inches apart.

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 in good shape. Resume watering as needed in late September as the plants come out of dormancy.

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 irises growing in mulched beds. 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 reducing weeds and maintaining soil moisture.

Louisiana irises generally set seed pods after flowering. These seed pods grow to be large and heavy, and if left on the plant will tend to make them lean over and look less attractive. Also, the production of seeds uses up a lot of food and energy that could be better put to use by the plant. So, as soon as all of the flowers have bloomed out, the flower spike should be removed to the point where it emerges from the foliage to prevent seed pod formation.

If you have never grown Louisiana irises, you'll be pleased by their easy care and beautiful flowers. If you already have some, consider adding some new colors to your collection.

Dan Gill is a horticulturist with the LSU AgCenter.