Bayou Beauties

A rainbow collection of flamboyant flowers on tall stems, sometimes reflected in still water, is a simple description of swamp irises…

Iris is the Greek word for ‘rainbow’, and amongst the different types of swamp irises, the Louisiana iris, native to the marshes and bayous of Southern Louisiana and growing along the banks of the Mississippi River across the southern United States, must be one of the most spectacular wild flowers!

Louisiana irises are actually cultivars of five species that readily interbreed, and are classified into the taxonomic group as Iris ser. Hexagona. As with many other perennials, like daylilies, irises in all their forms (there are 260 – 300 known species alone!) fascinate plant collectors and plant lovers so much that nature is assisted by human hands, and more hybrids are released every year by specialist growers.

Swamp irises are a clump-forming evergreen perennial with fans of slender strap-like leaves growing from an underground rhizome. Tall and slender flower spikes up to 90cm in height (depending on the hybrid) appear in spring to early summer carrying wide, six-petalled flowers with fascinating painted faces. For this pretty package to bloom in earnest, full sun is required. A little shade will be tolerated, but too much of it will result in poor blooming. The best climate for a swamp iris is moderate with light frost.

The main thing about swamp irises is a love for water: they will grow in bodies of water like dams, ponds or water features, and they will grow along the moist edges of streams or in a bog garden. Usefully, they will also grow equally well between other perennials in a normal mixed shrubbery.

Planting swamp irises in water

  • Use a large aquatic basket or a large pot to plant your iris in, as it loves to spread out.
  • Fill the container with good soil mixed with ample compost. Add an aquatic slow-release fertiliser tablet to the soil.
  • If planting a nursery-bought plant already in flower, keep it at the same level as it was in the bag. Add a bamboo stake to the container to enable you to stake it until it becomes established – they can be quite top heavy at this stage.
  • Submerge the planted container into the water so that there is about 5 – 10cm of water above the soil level in the container. Planting in the garden
  • Swamp irises like fertile soil deeply dug over and enriched with organics, so prepare the soil well with ample amounts of good compost and a handful of bonemeal or any other root stimulant.
  • Space plants about 50 – 75cm apart, with the rhizome just below the soil level – the soil covering the rhizome should be about 5cm thick.
  • As Louisiana irises prefer acidic soil, supply a layer of acidic mulch about 10cm deep around the plants. This is very important as the mulch will help to keep the soil moist between watering.
  • Regular watering is critical as the soil should never dry out completely.
  • Feed the plants with an acidic fertiliser in early spring and again in late summer after flowering.
  • Remove spent blooms to prevent seed pods forming by cutting off the flower spike where it emerges from the foliage.


Poor blooming can be caused by insufficient sun and overcrowding. Divide crowded clumps every 3 – 4 years after flowering or in autumn. Dig up the clumps, identify the healthiest rhizomes and replant them immediately in freshly enriched soil.

Other iris relations in a nutshell

We all get confused by the different plants in the Iris genus. Here is a simple differentiation of those most generally planted:

Bearded iris (Iris germanica)

The flowers consist of outer and inner petals known as ruffs and falls. Each fall has a fuzzy beard in a contrasting colour (mostly white or yellow) that looks like a tongue sticking out. This is the iris that we plant with its rhizome just above the soil level. Native to southern Europe and the Mediterranean area. Dwarf bearded iris From the same species as the tall bearded iris but with a much more compact form (20 – 40cm high). It is suitable for small gardens and is also more shade tolerant than its bigger relation.

Yellow flag iris (Iris pseudacorus)

Very vibrant and vigorous iris with yellow flowers on stems up to 1.2m in height. It easily naturalises in water and can be invasive – it is classified as a 1a invasive alien in South Africa and so must be removed if seen. Native to Europe, western Asia and north-west Africa.

Dutch iris (Iris x hollandica)

These are bulbous irises and were developed in Holland for the cut flower trade. We usually plant the bulbs in late autumn with other flower bulbs to flower in spring, after which they go dormant. The species is naturally from Spain.

Dwarf crested iris (Iris cristata)

Also called the woodland iris because it likes shady spots, this quick-spreading little perennial reaches 15 – 22cm in height. Native to the north-eastern United States.

Japanese iris (Iris ensata)

Tall irises up to 70 – 90cm that love to grow in full sun in water. Summer flowering and native to eastern Asia.

Large wild iris (Dietes grandiflora)

A robust, clump-forming iris with large white, orange and mauve flowers, this indigenous ‘iris’ is often used en masse in commercial landscapes. It grows in full sun to light shade and its flowering time is November to January. Native to coastal areas of the Eastern Cape and KwaZulu-Natal.

Yellow wild iris (Dietes bicolor)

Popular for mass planting with light-green, strap-like foliage and soft yellow flowers with dark brown to black markings from October to January. Another indigenous Dietes species commonly referred to as an iris, it is found naturally in Bathurst, Eastern Cape and on Lord Howe Island in the Tasman Sea.

The Gardener