Japanese Irises

Japanese irises, probably nowhere else, have achieved the cult status that is reserved for them in Japan. Although originally a simple water-loving species, the Japanese iris has been highly bred over the last 500 years to produce flowers of breathtaking beauty and, in the case of Higo iris, with one primary purpose in mind - that of indoor display.

In a highly ritualized ceremony with strict rules, along the lines of the tea ceremony and the specialized schools of flower arranging, a potted plant would be brought inside when the bloom was ready to open. There, to emphasize the beauty of the usually pure white or rich single color, it was displayed in front of a gold screen, to be watched, over a period of three days of quiet meditation, as the flower gradually opened to its ultimate beauty.

Long ago, the species I. ensata grew wild allover Japan, fulfilling a much more basic purpose. In the days before calendars, farmers would rely on seasonal changes to guide them in the growing of their rice crops. When the cherry trees blossomed it was time to start cultivating their fields. When the iris bloomed, the rainy season had arrived and it was time to transplant their rice plants from seedbed to paddy.

Inspired by the elegance of these simple flowers, Japanese hybridizers began experimenting with natural selections and cross-pollination as early as the 17th century. By the end of the 19th century superior new cultivars were being exported to the United States.

Also, in the latter part of that century, public gardens flourished around Tokyo where irises were grown in the paddy fields. City dwellers, seeking a brief respite from their crowded lives, would pay to view them. Gradually, three different strains of Japanese iris, each with its own characteristics, became recognized. Those developed in the paddy fields over a long period of time were named Edo, the ancient name for Tokyo. They produced flowers of great variation in size, color and form.

The Ise strain, named for the district of their origin, about 50 miles southeast of Kyoto, was developed primarily for growing in containers. Their blooms tend to be single in form with the falls in a pendent or hanging position.

Higo is an old province in Kyushu, and the irises developed there derived from the Edo varieties. They were also developed for containers, grown outside but brought indoors when they were ready to flower. Perfection of bloom was all-important, and because there was little interest in their garden performance, the development of plants with branching stems that produced a succession of flowers was unimportant.

Once the Higo strain became generally available and exported to the West, there was an increased interest in breeding these beautiful flowers for outdoors, though many cultivars were lost during World War II. Successive breeders, in both Japan and the U.S., have made crosses between the three strains and now, as the distinctions are fading, it is convenient to call them all by the term Japanese iris.

Culture

Plant Japanese irises about 3 inches deep in a rich soil that has plenty of organic matter. Fall is the best time to plant or transplant Japanese irises. Although these irises should have plenty of water during the growing season, they do not have to be planted next to ponds or other water features. Within three or more years, depending on their vigor and the number of increases, Japanese irises will become overcrowded. The crown will be approaching the soil surface, stems will be short and blooms will be sparse. That is the sign that it is time to lift, divide and transplant. You can divide and transplant right after the irises flower or in the fall when new root growth begins.

Soil with an acid pH is essential for success in growing Japanese irises. A pH of 5.5 is ideal. Because lime and limy soils are harmful to these acid lovers, do not plant them near fresh mortar work such as newly laid concrete patios, new foundations or newly mortared walls. Bone meal is a definite "no-no" for Japanese iris since this substance releases lime in the soil-indeed, today's bone meal is not very good for anything since so much of the nutrient value has been steamed out of it-better to use super phosphate instead.

To make your soil more acid, add 1 to 3 pounds of agricultural sulfur and plenty of humus or compost to each 100 square feet. Mix it in to a depth of 10 to 12 inches, then let it set for two to three weeks or more, depending upon the weather conditions, and then test the soil pH. Repeat the sulfur amendment if the pH is still too high. Lowering soil pH is more difficult than raising it. The speed with which the sulfur will lower the pH will be greater in warmer weather and in some soils.

Chelated iron products also will increase soil acidity when worked into the soil. Fertilizers formulated for azaleas and rhododendrons often have these materials in them. Japanese irises will indicate when the soil is too basic. The foliage will become chlorotic, that is, it will yellow although leaf veins may remain green. If this happens, you know that you must lower the pH, aiming toward the ideal of 5.5.

Heavy soil will suit these irises very well, so if your soil is light or even sandy in texture, be sure to add plenty of rich compost or humus to meet Japanese iris requirements. They are heavy feeders, so regular additions of organic matter to the soil will encourage vigorous growth. In cool climates, year-round organic mulches with a low pH-ground oak leaves, pine needles, well-rotted or dried manure, bark chips, wood chips or sawdust-will be beneficial in conserving moisture, deterring weeds and furnishing nutrients.

If you use sawdust or wood chips, remember that when these materials decompose, they use nitrogen in the process, so you will have to increase the amount of nitrogen in your fertilizer program. Beware of organic mulches in regions that have hot summers because they may encourage fungal diseases such as rot where there is high heat and humidity.

Some experts have said that manufactured (chemical) fertilizers appear to inhibit the growth of freshly planted Japanese irises. Once the plants have become established and have made a lot of new root growth, manufactured or organic fertilizers are important and will encourage vigorous growth and good flower production. As a general rule, apply fertilizers and organic mulches about three weeks to a month before the bloom season, then again in mid-August, about three to four weeks before the beginning of the fall root -growth period.

Gardeners used to think that Japanese irises could be grown successfully only near permanent bodies of water such as streams, lakes, ponds and bogs. This is not so. On the other hand, these irises do require plenty of moisture during the growing season. In order to produce large flowers, give Japanese irises plenty of water from the time you first see growth in the spring until a month to six weeks after the bloom period.

The plant needs enough moisture and nutrients for the increases, for the development of next spring's buds and for storage of nutrients in the rhizomes. The new plants will become semi-dormant for the summer months. You should cut back on watering somewhat, but never allow the soil to dry out. An active period of root growth begins again in early fall to store water and nutrients enough to last through winter and the spring burst of growth. Therefore, you should give the plant several heavy waterings during the fall months if rainfall is inadequate. Water if it does not rain for about two weeks, but also check the soil by hand to make sure it does not completely dry out.

Planting times for Japanese irises are in the spring or fall to coincide with the times of most active root growth. Home gardeners will find it easiest to transplant right after bloom when the roots are actively growing. The fall period of root growth is the period when growers will ship Japanese irises. Plants should arrive well before frost. If you put them directly into the garden, put each plant into a shallow depression in the soil to hold the water, lessen runoff and keep the roots deep in the ground. The rhizomes must be moist if they are to reestablish themselves well.

If they are potted rather than put directly into the garden, Japanese irises can develop a good root system in the pot, then be planted out wherever you wish in the spring. Plunge them into the soil for the winter season to avoid freeze-thaw cycles. If you establish these irises in pots, then you can plant them in the garden at any time of year. Whether Japanese irises are in the soil, in pots plunged into the soil or in pots in plastic pools, protect them from the destructive freezing and thawing cycles that plague the winter season.

If your climate or soil or both are not suited to growing Japanese irises, try growing them in pots outdoors or indoors, using an acid-type potting soil or mixing up your own highly organic, acidic medium. Rest the pots, which should be 6 inches or more in diameter, in a pan with an inch or so of shallow water so that the pots never dry out. If potted irises are grown outdoors, take them out of water pans and wading pools during winter months and protect them by plunging them into the ground and mulching heavily.

Plan to divide Japanese irises every three to four years. As they grow, the rhizomes rise closer to the soil surface and soon will be high enough in the soil to lack adequate moisture. When the roots don't get enough water, the plant will dwindle and may even disappear. If it looks like this is happening, dig up the plant, pot it temporarily and give it plenty of water, perhaps the plastic-pool treatment to get it growing again.

Growers in areas where the soil and water tend to be highly alkaline will have to keep track of the pH in the soil on a regular basis if they are to have success with the Japanese irises. Regular soil tests for pH should be a normal part of the regimen.

If your soil or climate does not fall within the recommendations for Japanese irises, do not give up. You can grow these beautiful plants in containers or raised beds. Prepare the acid planting medium for the containers or beds, using plenty of sphagnum peat moss or other organic materials with low pH readings.

Characteristics

The flower of the species is of a single form, with three upright small standards and longer pendent falls -the classic form still much admired by the Japanese and many purists. But frequently hybrids come in double form, with large standards, similar in size and appearance to falls that are broad and arranged horizontally, forming a large flat flower seemingly of six petals, almost circular in shape and sometimes frilled around the circumference.

Deviating even further from the species are some modern hybrids of multi-petaled or peony form where there are more than six 'petals' and the effect is of a much fuller flower.

In 1960 the first Japanese tetraploid cultivar (a plant engineered to have a double chromosome count) was bred by Currier McEwen in the United States, from I. ensata. Tetraploid cultivars have been available since 1979, and as more breeders succeed with this technique, the selection of flowers with exotic characteristics has increased. The flower color range of white, blue, mauve, purple and pink may at first sound limited. But these irises come also with a huge variety of patterns. Most are marked with a distinctive yellow signal on the falls, in place of the beard on bearded irises. In addition they may be veined with very fine, dark lines; they may be sanded -covered with small darker dots and very short broken lines; they may be brushed with minute dots, or edged around the falls and petals, or splashed with bold markings in white.

Blooming

Japanese irises extend the flowering season of the genus well into summer in some areas. When the glory of the tall bearded irises is just a memory for another year, when the first flowering of the Siberian iris is almost over, it is then that the Japanese display their beauty. By choosing a selection of early-blooming to late-blooming varieties, gardeners can enjoy these irises for a season of about six weeks.

Some cultivars will produce a second blooming that occurs about three weeks after the flowers of the first flush have faded. Seed pods and flowers therefore appear simultaneously on one plant. The ability to produce a second round of flowers, or remontancy, is dependent on the growing conditions but is a genetic feature of the plant. It will not happen merely because the plant has been pampered.

Species

I. ensata (syn I. kaempferi)

This is the original parent from which the Japanese bred their large-flowered forms and is distinguished by its heavily ribbed thick foliage. Not a true water or bog plant, it prefers rich, well-drained soil but requires copious water in spring and early summer. Garden forms must have good drainage and rich, loose soil.
This iris grows to a height of about 42 in (1.3 m) and the flower stem extends well beyond the foliage. The flower varies from dark red-purple through to white and shades of blue, with a narrow gold median stripe on the fall.

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