Growing The Hanashobu Iris aka Japanese Iris

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For more than 400 years the Japanese have cultivated a kind of iris almost entirely unknown to the average American gardener. Near Tokyo there is the garden Kotaka-en where these unfamiliar beauties have been grown and improved since early in the 17th century.

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What has kept them from American gardeners? Mostly the myth that they must be grown in water.

It is true that one iris species native to Japan, Iris laevigata, is a bog plant. And it is true that Iris laevigata once was thought to have been used in the breeding of the hybrids we call “Japanese Irises.”

But the most important species and perhaps the only one in their background is Iris Kaempferi which, though superficially similar to laevigata, is distinctly not a bog plant.

The Japanese call these spectacular garden hybrids “Hanashobu” but the term is unfamiliar here. We know them simply as “Japanese Irises” a misleading name which causes much confusion.

The Hanashobu, like the chrysanthemum and the flowering cherry, have been improved through the centuries by the skill and patience of expert flower breeders. They are one of the showiest of garden plants, but still infrequently seen. 

Today’s Hanashobu hybrids will grow four feet tall under reasonable garden conditions. They have flowers like silk brocade, measuring as much as ten inches across, and they will provide year-after-year bloom with just reasonable care.

In color preference, they range from white through blue and blue-purple to red and red-purple. Yellow is frequently present in the form of a striking signal patch.

Popular in the 1930’s

In the early 1930’s there was a surge of enthusiasm for these irises throughout the United States. The first US published descriptions of them were then available, and a number of plant growers rushed to import plants and seeds from Japan.

They also rushed to give names to nearly a thousand varieties, many so nearly alike that the average gardener could not distinguish differences. The result was confusion, and many people stopped growing the Hanashobu.

A scattered handful continued, and started breeding programs to improve the varieties. Slowly the hundreds of hastily named varieties disappeared. Slowly the work of the modern hybridizers began to produce results. Size was improved. Texture and substance were improved. Colors were cleaned up.

The hybrids of today are worthy of a place in any garden. The best of them are bred from the strain originated in Kumamoto Prefecture, Japan, called the Higo strain. They are characterized by extremely large double flowers in rich color patterns.

Japanese Iris Culture Is Not Difficult

Culture of the Japanese irises is not difficult, if a few requirements are observed. They will not tolerate an alkaline soil, and this is the item of greatest importance in Mid-America, where so many of the soils are rather alkaline. They are extremely heavy feeders. And they must have lots of water in the spring.

When you consider ordering your Japanese irises, prepare the beds ahead of time. Unless you live in our hottest and driest regions, they will prefer full sunshine. But if your summers are quite hot and dry, plant so that they are protected from the afternoon sun.

If your soil is neutral (pH 7) to mildly acid (pH 6.5) you need do nothing to it, but if you later notice the leaves of your plants turning yellow, you’d better check again. Your local water may be alkaline, and that may be affecting the plants. Check with a local water specialist on the best way to correct the condition.

Soil For Japanese Iris

Japanese irises will do well in good loamy garden soil, but for blossoms of the largest size, give them a rich bed of humus. An expert in their culture suggests the bed be dug out eight inches deep and refilled with a mixture consisting of equal parts of rotted manure, peat moss, and spent hops. Spent hops are a by-product of breweries, and are readily available in many areas.

This mixture is supplemented with commercial fertilizer of the acid sort, and a sprinkling of aluminum sulfate. This “red carpet” treatment is more trouble than the average gardener will care to go to, but it will produce top quality blossoms.

Whether you go all-out for them, or just stick them in the ground, do observe a few special things. Plant them deeper than your grown bearded irises. The rhizomes should be about two inches below the surface.

Water them well after planting, and keep them moist until they are established. Mulch them heavily the first winter, but do not use wheat straw or oat straw for the purpose. Japanese irises are susceptible to a wheat rust which is difficult to control.

Best Planting Time

As with most other irises, the best time to plant is late summer or early fall. You can plant any time with reasonable success, but for best results do it between the end of bloom and the first of September. Do not forget to water well, and to mulch well the first winter.

When growth begins in the spring the Japanese irises must have quantities of water. If it is possible to maintain bog-like conditions in the beds, so much the better. If this cannot be done, then water well and keep them good and soggy until they bloom.

Check the alkalinity of your water supply, too. If it is strongly alkaline, then take the steps to correct this. Keep the soil at least neutral, But do not allow the acidity to go much beyond pH6.

Blooming Time

The blooming season of the Japanese irises follows that of the tall bearded hybrids by about two weeks. If the end of bloom for your tall beardeds comes about June first, then expect your Japanese varieties to bloom about June 15th. The bloom will last from two to five weeks, depending upon how many varieties you plant.

As with other flowers, there are early and late blooming varieties. A mixture is required to enjoy the maximum period of bloom. The Japanese irises require a bit longer to get settled than other irises. First season bloom will never be typical, but by the second they should be well established.

After the bloom season the beds may be allowed to dry out a bit, but should never become bone-dry or baked. If your normal annual rain fall exceeds 30 inches, no summer or fall watering should be necessary. Unless, of course, you get all 30 inches in one spring month.

When to Feed

In the fall, apply a dressing of well rotted manure. If you dislike the use of animal manure because of the weed seeds it imports, then use any of the complete plant foods on the market.

The important thing is that Japanese irises are gross feeders, and quickly exhaust the available food. Unless this is regularly resupplied, the stalks will become shorter, and the blossoms smaller and fewer. It is important that this feeding be done in the fall, not in the spring or summer.

If you are fortunate enough to have a boggy area, or a stream, you may safely plant the Japanese irises near the edge. If your winters are mild, you can even plant right in the water. But in cold areas the Japanese irises resent winter wetness.

Here is a new plant, though it is hundreds of years old. Here is a plant with spectacular bloom, and one sure to amaze every garden visitor. You should try a few!