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Japanese irises yield spring, summer color
By Norman Winter
Central Mississippi Research & Extension Center
The past few years have given me a new appreciation for the various iris species available to Southern gardeners. With careful selection, we can enjoy a long season of iris blooms.
Everyone ought to consider the Japanese iris, known botanically as Iris ensata. It complements the Louisiana and Siberian irises with toughness, beauty and blooms that are born in glorious summer displays after the other irises have finished. They flourish from zones 4 to 9.
The Japanese iris produces large blossoms in shades of blue, pink, white and purple, with bicolored stripes, veins and blotches. They are available in single-, double- and peony-flower forms. They are also tall, reaching 24 to 30 inches in height. These are a must for extending your iris season. The foliage -- bright green with a prominent rib -- is equally attractive.
Japanese irises perform best with at least six hours of sunlight per day. The soil should be fertile, organic-rich and acidic. Tightly compacted soils yield an inferior, stunted-looking plant. If this describes your soil (like it does mine), you should amend with 3 to 4 inches of organic matter and till to a depth of 6 to 8 inches.
While tilling, incorporate 3 pounds of a 5-10-5 fertilizer per 100 square feet of planting area.
Container-grown irises that you see in the spring and summer can be set out at any time during the growing season at the same depth they are growing in the container. Space the plants 12 to 18 inches apart. In the fall, plant rhizomes just below the soil surface.
Japanese irises are heavy feeders, so give light applications of a 12-6-6 fertilizer in the early spring and every four to six weeks throughout the summer. Do not let plants dry out after fertilizing, as this will quickly burn plant roots. Keep the soil evenly moist during the growing season.
The best blooming occurs on 2- and 3-year-old clumps. Plants under good culture require dividing in the spring or fall every three to four years. Maintain a good layer of mulch year-round to conserve moisture and to moderate soil temperatures.
The Japanese iris complements a water garden, pond or creek and actually can be grown in water. However, they do just as well in fertile upland soils. Plant the Japanese iris boldly in informal drifts. Some of the prettiest displays are with other Japanese irises placed in groups of different colors. The large leaves look striking in the tropical garden when combined with elephant ears, ferns and bananas, and in front of larger ornamental grasses.
There are more Japanese iris varieties than you ever dreamed. Garden centers stock more every year, and Mississippi specialty growers have a good selection. Favorites are Cry of Rejoice (purple with yellow center), Diomedes (blue), Rikki-Pikki (white), Loyalty (violet-blue, double blossoms and yellow striping on the falls) and Sapphire Star (pale lavender with white veins).
Spring is hitting the Coast and is within sight of the Mississippi-Tennessee border. All gardeners within those boundaries can grow the Japanese iris. I doubt there will be a single complaint from anyone who gives them a try.