Culture
Best grown in humus-rich, medium moisture, well-drained loams in full sun. Best flowering and disease resistance occur in full sun. 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 must be amended prior to planting (e.g., add gypsum, coarse sand, organic matter) or raised plantings should be considered. Plant rhizomes shallowly in mid to late summer (July to early September) with the rhizome or root just above the soil surface. Rhizomes planted too deep are susceptible to rot. Fertilize lightly in early spring. Fertilize again after bloom. Continue to provide uniform moisture throughout the summer to encourage a late summer to fall rebloom. Avoid overhead watering. Deadhead individual spent flowers and remove flowering stems to the ground after bloom. Divide plants when overcrowding occurs (every 3-4 years).
Noteworthy Characteristics
'Florentina‘, commonly called florentine iris, is a tall bearded iris which grows to 23-29" tall and to 18-23" wide. It is comes from Italy and southern France. Bloom occurs late spring to early summer. It slowly creeps by rhizomes. Fragrant flowers feature standards and falls that are soft white tinged gray-blue, with contrasting yellow beards on the falls. Sword-shaped, linear leaves (to 12" long and 1 1/2" wide) grow in a clump of about 6 leaves per tuft. Flowering stems rise well above the leaves to 2 1/2' tall.
The rhizomes of this iris along with the rhizomes of Iris pallida and Iris germanica are the source of the dried orris root of commerce. Rhizomes can be dug in late summer, peeled, chopped up, dried, aged, and then ground into a powder which can be used as a scent fixative for perfumes and potpourris. Orris root has a violet-like aroma. Powder is added directly to potpourris, but first distilled into a cream-colored butter or oil prior to being added to perfumes. Orris root is used today in a number of different perfumes.
Problems
The major insect pest of bearded iris is iris borer. Major disease problems are bacterial soft rot and fungal leaf spot. 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.