Culture
Best grown in rich, well-composted, humusy, medium moisture, neutral to slightly alkaline, well-drained soils in full sun. Best flowering and disease resistance occur in full sun. Plants will tolerate light shade. Best with consistent moisture during growth periods, but avoid wet soils. Many spurias are summer dormant and need much less moisture after bloom (growth in summer often stops during hot weather and plants can survive with little watering). Good soil drainage is essential to combat potential soft rot problems. Avoid use of mulch for the same reason. Heavy clay soils such as those present in much of the St. Louis area should be amended prior to planting (e.g., add gypsum, coarse sand, organic matter) or raised plantings should be considered. Plant rhizomes shallowly (about 2" deep) and about 24” apart in mid to late summer (July to early September). Fertilize regularly in spring prior to bloom. Avoid overhead watering. Deadhead individual spent flowers and remove flowering stems to the ground after bloom. Divide plants immediately after flowering when overcrowding occurs (every 3-4 years).
Noteworthy Characteristics
Iris spuria, commonly called salt marsh iris or butterfly iris, is a tall, rhizomatous, beardless iris that is native to central and southern Europe and from Algeria to Iran. It is one of the tallest members of the iris family, with stems typically rising to 3' (occasionally to 5') tall. Stalk height is often reduced in cold winter climates. Grows in clumps with attractive narrow linear leaves (to 3-4' long). Flowers on species plants typically have bluish-purple to lilac segments with falls sometimes having a yellow ridge. Color variations expand the color range to include white, blue, purple, wine and brown.
Subsp. carthaliniae is native to the Caucasus and Georgia. Flowers (to 3" diameter) bloom sky blue with darker veining. Well suited for the back of the border or pond edges. Thick, branched rhizomes. Lanceolate sheathing leaves. May-July bloom.
Genus named for the Greek goddess of the rainbow.
Specific epithet means false.
Problems
A major insect pest is iris borer. Other potential insect problems include iris weevil, slugs, snails, thrips, whiteflies and verbena bud moth. Major disease problems include bacterial soft rot, crown rot fungus, rhizome rot, and fungal leaf spot. Watch for mottling of leaves and flowers which may indicate the presence of mosaic virus. Mustard seed fungus can be fatal. Good sanitation practices are the most important component of any disease/insect control program: promptly remove and destroy diseased foliage/rhizomes, promptly remove and destroy borer-infected foliage/rhizomes and perform an annual clean-up of all debris and foliage from beds in fall after frost. The most frequent causes of failure to flower or sparse flowering are (1) rhizomes are planted too deep, (2) plants are located in too much shade, (3) plants were given too much fertilizer or (4) plants have become overcrowded and need division.
Uses
Sunny beds and borders. Will naturalize into large clumps.