Louisiana irises are great for planting on pond edges. (Photo by Allen Owings)

Late fall and midwinter are the times when Louisiana irises are growing actively. (Photo by Allen Owings)

News Release Distributed 12/13/13

By Allen Owings
LSU AgCenter horticulturist

HAMMOND, La. – Louisiana iris is our state wildflower. Five species of these native plants are collectively referred to as Louisiana irises – Iris brevicaulis, Iris fulva, Iris giganticaerulea, Iris hexagona and Iris nelsonii. All five species occur in south Louisiana. You typically see them growing in damp or wet areas at the edge of swamps, in boggy areas or in roadside ditches.

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 hybrid Louisiana iris varieties we grow today. Their large, attractive flowers come in a wide range of colors, including many shades of blue, purple, red, yellow, pink, gold, brown, lavender, burgundy and white. Varieties with bicolor flowers, bright yellow signal markings or ruffled petals add to their beauty.

The active growing season for Louisiana irises is different from most herbaceous perennials that are typically dormant in winter. Louisiana irises begin to grow as the weather cools down in October and continue to grow until April when they bloom. That means you can now see active growth and vigorous foliage on Louisiana iris.

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 will ensure the best blooming.

Louisiana irises can be planted in three types of situations – in beds containing only Louisiana irises; in beds with irises mixed with other plants, such as annuals, perennials and shrubs; in an aquatic culture. Landscape beds containing only Louisiana irises can be outstanding and can be a showstopper in the spring landscape.

Louisiana irises prefer an acid soil with a pH of 6.5 or somewhat lower. However, they are adaptable and also will grow well in soils that are slightly alkaline. A soil high in fertility and rich in organic matter will encourage vigorous growth and abundant flowers. Mulch landscape beds of Louisiana iris with pine straw.

Guidelines from the LSU AgCenter and the Greater New Orleans Iris Society include:

– Fertilize established beds in September or October and again in late February or March.

– In fall, use one pound of 8-8-8 fertilizer, or equivalent, per 10 square feet of iris bed; in spring, use the same amount – or a bit less.

– Regularly remove and discard any foliage that yellows. Don't compost the yellowed foliage because it can harbor rust disease.

– Keep the beds consistently moist. If the irises get too dry, they will cease growing and the foliage will not be attractive. The plants will resume growing in fall, however.

– Remove flower stalks after the bloom season unless you want to harvest seeds in late June or early July. Cut stalk to within an inch or so of the ground.

– If the stalks are not removed, at least remove any seed pods before summer to avoid unwanted seedlings popping up among existing plants.

– Divide irises after three to five years or if they lose vigor. Replenish soil as if creating a new bed.

The Louisiana Iris Society is partnering with the LSU AgCenter to establish a Louisiana iris demonstration garden at the Hammond Research Station. This collection will include all the species of Louisiana iris in addition to older historical varieties and a wide array of the currently available popular varieties. Plantings have been initiated and will continue through 2014.

You can see more about work being done in landscape horticulture by visiting the LSU AgCenter Hammond Research Station website. Also, like us on Facebook. You can find an abundance of landscape information for both home gardeners and industry professionals at both sites.

Rick Bogren