World of Irises: Understanding Louisiana Iris, Part 1: I. giganticaerulea

Sunday, March 8, 2015

Understanding Louisiana Iris, Part 1: I. giganticaerulea

By Joe Musacchia

The Louisiana Iris is one of the most misunderstood yet versatile irises. It’s been called a water iris, which is not technically correct. Some will grow in water, some will not. If the foliage is totally submerged, they will most likely die. Most will grow well in bog conditions, but some will not. They have been grown from Canada to Mexico and in many countries abroad. They grow from the marshes and swamps of Louisiana to the deserts of Arizona. The secret to their successful cultivation is understanding the cultural differences of the five species that make up this diverse group of iris, and being able to recognize these traits. The species that make up Louisiana iris are I giganticaerulea, I fulva, I brevicaulis, I nelsonii, and I hexagona. Most of the new cultivars on the market today have all 5 species genes in them. My purpose here is to help you to look at a cultivar and recognize these traits, so that you will have some idea how this cultivar will perform in your garden and what culture requirements are best.

I. giganticaerulea

Iris giganticaerulea (or giant blue) is the tallest of the Louisiana Irises. It can grow over 6 feet tall in the right conditions. It was discovered and named by Dr.John K. Small in 1925 while he traveled by train through South Louisiana.

Iris giganticaerulea growing on a bayou side

In its native area I. giganticaerulea grows all winter. Hot, dry summers may bring on dormancy, with the plant all but disappearing until late August when the weather cools, and rains return. It is most commonly found in marshes, along bayou banks, in ditches, and the edges of swamps. It can be seen growing in as much as 2 feet of water. Even so, if the plant goes dormant during the summer, an early return of standing water can spell their demise if the growing tip is submerged for an extended time.

White I. giganticaerulea
( Barbara Elaine Taylor )

I. giganticaerulea blooms very early in the spring with rapid bloom stalk development. The flowers are very large, generally 4-6 inches across. The color is a blue-purple with an underlying white. A white form, lacking the blue pigment, has been collected in the wild and brought into cultivation. They require a lot of sun during their growing season (winter in Louisiana), but will tolerate some light or afternoon shade in the peak of summer in that region. They possess tall, straight stalks with little or no branching. Their rhizomes tend to be large, and will often grow a foot or more in a growing season, causing the plant to travel.

One year winter growth

I. giganticaerulea’s core traits have an implication on their performance in various geographic locations. Because they bloom early, hybrids that have strong giganticaerulea traits may not perform as well in areas outside their normal range. Most commonly, unless the rhizomes are directly exposed to extreme temperatures (as in the case of frost heave), the plant will survive and grow, but might never produce bloom. In New York State for example, where spring freezes are common, the tender, early bloom stalk will succumb to the assault. You will get a lot of lush green foliage all summer, but no flowers. Between the early bloom season, the tendency for the rhizomes to travel in beds, not to mention the need for division every two or three years, some find them a difficult plant to employ in a home landscape. These same traits make them ideal for landscaping around ponds, rain gardens and areas where too much water is a problem. Recognizing these traits in modern hybrids can help you select the best Louisiana cultivar for success.