Iris tectorum is a widely cultivated garden plant. The specific epithet “tectorum” means “roof of the house.” In the past, wall iris used to be grown on the roofs of houses in Japan and China.
I. Appearance and Characteristics
Iris tectorum (also known as roof iris, Japanese roof iris and wall iris) is a plant species in the genus Iris, it is also in the subgenus Limniris. It is a rhizomatous perennial. It is native to China, Korea and Burma, with lavender-blue, bluish-violet, purple-blue, blue-lilac or sky blue flowers. There is a white form as well. It is a compact plant and is cultivated as an ornamental plant in temperate regions of the world.
It has a thick, (the size of a man’s thumb), creeping, buff (coloured), or greenish rhizome. They are similar in form to a bearded iris rhizome. It has slender, short roots (under the rhizomes), and fibres on the top. The creeping habit creates spreading clumps of plants. It does not produce stolons.
It has basal fans that are yellowish green, or pale green, and sword-shaped (ensiform), or lance-shaped. They are also glossy, and ribbed, and can grow up to between 15–60 cm (6–24 in) long and 1.5–5 cm (1–2 in) wide. The leaves are floppy, and described as semi-evergreen.
It has terete (cylindrical)stems that can grow up to between 20–45 cm (8–18 in) tall. It has 1–2 branches, and 1–2 (reduced) stem leaves.
The stems have 2–3 spathes (leaves of the flower bud), that are green, lanceolate and 3.5–7.5 cm (1–3 in) long and 2–2.5 cm (1–1 in) wide.
It has a 1 cm long pedicel (flower stalk), which is shorter than the spathe, but similar in size to the ovary.
The stems (and the branches) hold between 1 and 3 flowers, in late spring, or early summer, between April and May, or June. It flowers between September and October in Australia. The flower display can last for 2 weeks. The flowers are 7.6–10 cm (3–4 in) in diameter, The flattened, horizontal, flowers are larger than Iris japonica flowers.
The flowers come in shades of lavender blue, or bluish violet, or blue-lilac, or purple-blue, or sky blue. There is also a white form.
It has 2 pairs of petals, 3 large sepals (outer petals), known as the ‘falls’ and 3 inner, smaller petals (or tepals), known as the ‘standards’. The falls are obovate (egg-like), or ovate, with darker (or brownish purple/violet). mottling, veining, streaks, or spots, around a toothed or lacinated (fringed), white crest. They have a bi-coloured claw (part of the petal closest to the stem), white and violet or lilac. The falls are 5–7 cm (2–3 in) long and 4 cm wide. The elliptic standards spread horizontally (not erect), and are 4.5–5 cm (2–2 in) long and 3 cm wide. Both petals (falls and standards) can have wavy margins.
The flowers are self-fertile, but are pollinated by insects.
It has a 2.5–3 cm long slender, perianth tube, a 2.5 cm long stamen, bright yellow anthers and a cylindrical, 1.8–2 cm long ovary. It has a pale bluish-violet style branch that is 3.5 cm long. It has toothed lobes (at the tips), that are irregular.
After the iris has flowered, between June and August, it produces an ellipsoid or obovoid (oblong-ovoid), light green, seed capsule. It is 4.5–6 cm (2–2 in) long and 2–2.5 cm wide, and has 6 ribs. When it ripens, (and goes brown,) it splits in three, along 2 or more seams, starting from the top. Inside, are multiple, black-brown seeds, which are pyriform (pear shaped) and have a small cream (coloured) aril (appendage).
Like many other irises, most parts of the plant are poisonous (rhizome and leaves), if mistakenly ingested, it can cause stomach pains and vomiting. Also handling the plant may cause a skin irritation (like dermatitis or an allergic reaction.
II. How to Grow and Care
Sunlight
Wall iris likes sufficient sunlight. It needs to receive more than 6 hours of light per day and can be planted in a garden with no shade. It can also grow in slightly shady environments, but the quality of its blooms and disease resistance may decrease. Some varieties tolerate environments with less light and can grow in the shade of other plants.
Temperature
plants of the Iris genus are mainly distributed in the temperate zones of the Northern Hemisphere. The majority of its species are hardy, except some dwarf species that require hay or bark to cover their roots to overwinter in cold regions. The need for water among different Iris species varies, too. Some Iris likes moist environments, and some species can even grow in water.
Watering
Different Iris species’ needs for water vary. Bearded iris requires very little water, and only needs to be watered when the soil is dry. Other species, such as Siberian Iris (Iris Sibirica), need much more water and require the soil to be kept moist all the time. Most species are intolerant of standing water. When planted in poorly-drained soil, their roots may rot.
Soil
Wall iris likes loose, fertile, and well-drained soil, but can also grow in dry and barren earth. It likes slightly acidic or neutral soil with a pH value of 6.0-7.0. Sulfur can be added to improve alkaline soil, while lime can be added if the soil is acidic.
Fertilizing
Wall iris likes soil rich in humus, so fertilize in the early spring, early fall, and before its flowering period. Before it blooms, use phosphorus-rich compound fertilizers, such as fertilizers with a 5-10-5 NPK ratio, to promote blooming and encourage more gorgeous flowers. Balanced fertilizers (20-20-20 NPK ratio) can also be used. Some organic fertilizers contain fewer nutrients but improve the soil, so it is also good for the plant’s growth. Water right after fertilizing to help the roots absorb the fertilizer.
Planting Instructions
It’s best to plant wall iris in the summer. Choose a spot with ample sunlight and good drainage, and turn up the soil to 25 cm deep. Then topdress with fertilizer and mix in evenly. When planting, you can cut the leaves to 15 cm in length, which helps reduce water evaporation and increase the survival rates. Finally, cover the rhizome in the soil. Avoid letting the roots get dehydrated for too long during planting, and water right after planting.
Pruning
Cut off the bloom-bearing stalks after blooming to reduce nutrition consumption. Some varieties may bloom again. In the fall, prune old and dry leaves to improve the plant’s inner ventilation and prevent pests and diseases.
Propagation
Because seeding may result in changes in the colors and shapes of flowers, it’s best not to propagate the plant by seeding. Wall iris can be propagated by division, and it is usually carried out 2-3 months after blooming. Divide the plant with a sharp knife, retaining a 15 cm-long rhizome on each piece. Cut off the old, dried parts and trim the leaves to 15 cm in length. Keep the plants 30 cm apart from each other (for dwarf varieties, the distance can be reduced to 15 cm).
Transplanting
Early spring to late summer (S1-S2) is optimal for transplanting wall iris due to its vigorous growth phase. Ensure a location with partial sun to deep shade for successful growth. Remember, wall iris relishes well-drained soil and thrives best when clumps are not overcrowded.
III. Uses and Benefits
- Ornamental uses
Wall iris produces large blossoms that add floral interest and color to sunny or partly-shaded garden areas. It also does well in rock gardens because it does not need much water. However, this bulb can also thrive around ponds and fountains and quickly naturalize, covering large areas as a groundcover.
- Medicinal uses
Despite its toxicity, it is used in Chinese herbal medicine to treat hepatitis and wind damp pains.
The Kam eat fish that have been given fresh Iris tectorum, as medicine to treat stomach aches.
IV. Harvesting and Storage
Wall iris flowers can be harvested for bouquets. Choose not-fully-bloomed flowers and cut them off from the stem base obliquely with a pair of sharp gardening scissors. Quickly put the flower in a vase with clean water to avoid its dehydration.
