Iris Doctor

By M. D. Faith

M. D.

I do have a few questions concerning the care of my Louisiana irises... Your answers will be greatly appreciated if received sometime before the first blizzard of the Arkansas winter … respectfully, a "potted" iris lover.

Do Louisiana’s survive the hard cold weather as our favorite tall bearded do?

Most of the Louisiana iris grown here in Arkansas and Oklahoma are cold hardy iris, and can stand the winter with out damage. This is due in part to the work of our own Arkansas hybridizers, Frank Chowning, Henry Rowlan, and Richard Morgan. They used iris brevicaulis and iris fulva derived hybrids in their breeding programs to add cold hardiness to their seedlings. Iris brevicaulis is native to the rivers, swamplands, and streams ranging to the northern borders of the United States and even into Canada. Iris fulva occupies the same habitat ranging as far north as Missouri and Ohio. So most of the cultivars grown locally are cold hardy hybrids. They even survive in North Dakota and Minnesota with heavy mulching in the winter.

Louisiana iris hybrids out of iris giganticaerulea are more sensitive to severe winter cold. This species native habitat is along the warm southern gulf coast with the heaviest concentration on the Louisiana gulf coast. Thus hybrids with this specie in there back ground are subject to being damaged or killed in winter in our area. Bloom stalk damage is usually the most likely thing, resulting in no bloom or scant bloom.

We normally use mulch of two to four inches on Louisiana iris to protect the rhizomes from the summer sun and conserve moisture. Just leave that in place, or possibly add a new layer on top to take care of that which has decomposed, and they should go through the winter without any loss due to the cold.

If Louisiana’s are grown in pots within a larger container filled with water will the freezing temperatures damage the rhizomes?

Container plants are another thing, because the whole plant is above ground and subject to the full force of winter cold. If possible they should be moved to a southern exposure on the south side of a building or other structure which will give them protection from cold north wind.

As you move and bunch the plants, you should pack leaves, straw, or other insulating material around and between the containers, putting three or four inches around the fans and on top of the containers, also. Those that were or are in pans of water should be limited to pans that are no taller than one-fifth the height of the container.(2” for height of 10”).

Should growing methods change for the winter months?

Growing conditions should change for the winter months for two reasons.

1.) Early fall and early winter comprise the first half of the Louisiana iris’s prime growing season. In fact, the time to set new Louisiana iris beds is in late September and October. They will grow rapidly during this period, if given proper care, until we start getting repeated hard freezes. This generally does not occur until late December or early January. The foliage may winter kill during the hard cold winter months of January and early February, but will put up and resume growth during it’s second growth period, prior to bloom, in late winter and early spring, starting approximately mid-February. Rapid and robust growth will be achieved by the last of March into April. The bloom season will begin in late April and continue through the first 15 to 20 days of May. Some late blooming cultivars may extend the season another 15 days.

2.) The summer months, mid-June, July, August, and perhaps early September are spent primarily watering or irrigating in an effort to keep the rhizome from going dormant. Summer dormancy will cut your following spring bloom considerably, so is to be avoided if at all possible. Early summer, just after the bloom in May or the first of June, is the time to feed Louisiana iris for the second time. The first having been applied in February, with the last to be applied the first of September. These feedings coupled with a faithful adherence to a proper irrigation schedule will go a long ways toward avoiding a summer dormancy period. Summer is a good time to apply mulch to prevent the sun from scalding the rhizomes and to protect from winter cold, as well as conserving moisture, which helps pay the water bill.

In our areas where rainfall for Louisiana iris is generally inadequate, if it does not rain we must irrigate. The tendency is to ignore the water requirements during the fall and winter months, but this is a bad mistake for this is a prime growth period for Louisiana iris.

Should the rhizomes be completely covered by soil or are the rhizomes resistant to freeze?

As previously explained, cold hardy bred Louisiana iris are resistant to freezing. We do, normally, completely cover the rhizome with about one to two inches of soil when transplanting or, at the very least, flush with the soil surface covered with two to four inches of mulch. They will not remain below the soil surface, however, but will crawl out and run along the soil surface as they elongate in growth.

We most often think of the rhizome as a root, and part of the root system of the plant. It in reality is a horizontal stem that creeps along the ground for support with roots below to draw in plant food, and leaves above to catch the sunlight for photosynthesis transforming all into one of the most beautiful plants known to man. Which, we all love with a passion!