A member of the section Lophiris, Iris tectorum is still often referred to as an Evansia Iris which was the designation given to all the crested iris by Salisbury in 1812 to honor Thomas Evans who introduced one of the crested species to cultivation in England. The plant of I. tectorum somewhat resembles a bearded iris. I. tectorum does not have a bright signal patch as many of the beardless irises do, nor does it have a beard on the falls. In place of the beard or signal I. tectorum has a crest, a cockscomb or raised ridge of petal like material. This crest is the distinguishing characteristic of this group of irises.
The fans of I. tectorum consist of wide leaves of a rather thin texture and are heavily ribbed. Each leaf is about one and one half inches wide. The whole plant is a little over one foot tall. The rhizomes are fat and look much like a bearded iris rhizome. The flower stems are sometimes branched and carry two or three flowers from each set of spathes. The flowers are about the largest of this section, being three to four inches across. The falls are flared and the standards open outwards rather than being upright.
The color range of this iris is limited to slightly varying shades of lavender with dark purple spotting on the falls. The form grown by Aitken's Salmon Creek Garden has much heavier spotting than most forms Dr. Waddick collected a plant in the Woolong area of China with wider petals. However there is usually little variation in color and form in this species except for a pure white form that is quite spectacular and generally comes true from seed. The I. tectorum with variegated leaves just offered this year by an east coast grower is reported to be a miffy grower. If it grows well in our climate it should be a showy addition to our shade gardens.
I. tectorum is native to central and southwestern China but has been cultivated for so long in China and Japan that the boundaries of it's original habitat are clouded. The women of Japan use the powdered rhizomes as a face powder. Because land was at such a premium all of it was used for food crops. The Japanese women not wanting to give up their cosmetics began to grow the iris on the thatched roofs. It has been grown there for centuries and is commonly known as the "Roof Iris". It is also thought to ward of evil spirits and is said to help hold the thatch together. We will probably never know which of these reasons was the original one that elevated I. tectorum to the roof tops.As a garden plant I. tectorum is superior. It will grow in full sun or full shade. In full sun I feel the leaves bleach a bit and are not as deep a green. In full shade mine grow and bloom well but might do better in half shade. All of the iris in the crested group are plants liking woodland conditions. A rich soil high in humus kept slightly moist at all times is to their liking. They are all heavy feeders so a dressing of compost or manure in fall and a bit of low nitrogen (5-10-10) fertilizer in the spring is beneficial. These are the optimum conditions but I have seen I. tectorum growing in full sun, in heavy shade, baked dry at times and still blooming well. It is a very adaptable and sturdy plant. The one problem with this plant is that it often becomes virused which causes yellowing and streaking in the leaves and a general decline in the plant. If this happens, save seed and start a new plant as plants started from seed will be virus free. Then destroy the old plant. Plant the new seedlings in a different place from where the virused plant was growing. This happened to my white form once but the new seedlings I have been growing for six or seven years have remained virus free and they are only about ten feet from where the old plant was.
The easiest method to obtain this plant is to purchase rhizomes in the fall. Many growers offer it in their "other or species" sections. There are usually a few starts offered at the KCIS Beardless Sale in September. Another way to get started is with seed. Many of the seed exchanges offer both the blue and the white forms. If you grow it from seed grow on several plants to blooming size and then chose the form with the best flowers and the best branching as they will vary somewhat.