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No Louisiana Iris sales website is complete without instructions on how to care for your new plants. Cruise the internet and information with the writer’s bias abounds. Definitive recommendations for bed preparation, soil pH, fertilizer types and schedules, watering, mulching, and specific plants that will “grow in your area.” It’s all there.

The one sure thing I have learned about growing Louisiana Iris in Central New York is, snow (and lots of it) is your best friend; it’s why it works! Our snow cover blankets the plants through the coldest of the winter, protecting the delicate growing tips. The spring melt provides copious amount of water for plants in rapid growth as the soil warms in the lengthening days.

Culture information provided below is the result of trial and error and best guess practices derived from assimilating the mass of instructions geared toward Southern growing, and applying years of practical Northern gardening experience. If you are purchasing rhizomes for zone 7b – 9 gardens, I would refer you to publications found on the Society for Louisiana Irises website (click here) or from the LSU Ag center (click here).

If you‘re looking for the executive summary, here are the basics.

  1. Give your new rhizomes a good overnight soak before you plant them. Get them in the ground as soon as possible.
  2. Sun, and lots of it. No… more than that. Full sun.
  3. Water, not necessarily a pond, swamp or wetland, but good even moisture throughout the growing season.
  4. Fertile soil. Not too alkaline.
  5. Fertilize… abundantly. Louisianas are heavy feeders. Apply a balanced N-P-K fertilizer about a 6 weeks before bloom (roughly early May), and a balanced N-P-K after bloom (roughly late July to mid-August).
  6. As late in the fall as you dare, cut the fans back to nubs (being careful not to injure the growing tips – about 2 inches is good). Cover with a lofty mulch. The dense mulch we tend to favor for our northern perennial borders is considerably less satisfactory than loose, airy pine straw mulch that will trap air beneath the snow and thus better insulate your rhizomes from temperature extremes.
  7. Leave the mulch in place as long as you can stand it. Late spring freezes are a bloom killer. My guideline is that the mid-season tulips must be well into bloom before I peek.

Expanded Cultivation Tips

When you receive your rhizomes, remove them from their packing and place them in a shallow container of water. They will have been packed with a small amount of a silica based material to hold moisture during shipment, but will benefit from a good soak, at least overnight, before planting. If you refer to the drawing above, you can see that the rhizome is actually an underground stem, with fibrous roots below and a fan of cut leaves at the growing tip. Don’t worry if the leaves appear a little yellow or soft on your rhizome. This is a result of the disinfection process employed before shipping. Any damaged leaves and roots will be sloughed off after planting, and new growth will be unaffected. You may notice white nubs or small leaves along the length of the rhizome. These are offsets, or “increase” and will be the start of next year’s rhizomes. Try not to disturb them during handling and planting. Unlike bearded iris rhizomes, Louisiana's should be planted just below the surface with the roots spread across a bed of loose soil. I like to add some well-composted manure to the hole before covering the rhizome and giving it a generous soaking of water. Over time, the rhizomes will move to the level they prefer, generally coming to surface level over time. Placing the rhizome beneath the surface initially however, will aid the plant in its first wintering-over.

When selecting a location for your new plants, look for the sun. In the semi-tropical swamps and wetlands of south Louisiana, the wild irises emerge from semi –dormancy in late February, when the Tupelo and Bald Cypress are still leafless. They grow rapidly and send up tall flower stalks in the bright sun. After blooming and forming seed pods, the irises settle into summer dormancy beneath the thick canopy. Leaves die back and the plants retreat into the swamp until late August or early September, when the temperatures cool and fresh leaves begin to appear. What this translates into for the Northern garden is, the more sun, the better. Dormancy patterns are altered up here. Spring means the plants must get up quickly and full sun is the key. Irises in the south have been growing slowly throughout the winter and are one of the earliest flowers seen. In the north, latent cool spring temperatures keep growth slow well into May, finally erupting in early June and providing a early summer bloom (late June –early July in Zone 5, early – mid June in Zone 6). Full sun is their friend.

Northern grown plants, given a reasonable amount of water during high summer will continue to grow well into the fall. In fact, the cut back fans will often protrude a foot or more through the first snows of winter, only going to ground when they are finally covered over and the ground is frozen.

There is a common misconception that Louisiana Irises are a water plant. While they will grow happily in a backyard pond or water feature, they are equally adaptable to a range of garden soils. There are just a few things to keep in mind. Traditional wisdom stated that optimal soil pH for Louisianas is 6.5 or a bit lower. There has recently been much debate about this amongst growers. There are a number of growers that find their plants are doing just fine in a slightly alkaline soil. Anecdotal evidence notwithstanding, if your soil does tend to be very alkaline, I’d encourage you to amend your soil to at least a neutral range. Work in plenty of compost or other organic rich materials to encourage a healthy soil structure.

Louisiana irises are very heavy feeders. If you consider that their natural environment are the fecund swamps of the Gulf coast, immersed in the rich organic run-off of the Mississippi River, it’s not hard to understand that generous fertilizing will promote the same lush growth in your garden. In our garden, a 10-10-10 (or 12-12-12, depending on what is available) granular fertilizer is applied at the recommended rate following bloom season (somewhere between mid July and mid August). This will give the plant plenty to work with before the snow falls. Water the fertilizer in well. Approximately four to six weeks before expected bloom (early to mid May in our zone 5b location), apply a balanced N-P-K fertilizer. Unlike Louisianas growing in the Southern zones that enter a semi-dormancy during the scorching heat of June through August, Northern grown irises will continue a robust growth habit throughout the summer. During this time it will help if you monitor the soil for adequate moisture, but it is generally unnecessary to water unless you are experiencing extended dry periods. Remember… it is almost impossible to over-fertilize a Louisiana iris.