Japanese Irises
Japanese irises have very large, exotic blooms. Although the colors available are limited
to white blue and shades of purple; the variation in shape is unmatched. These
delightful irises bloom after the tall bearded variety and extend the iris season into July
in the Northeast. Japanese iris have no beards and their iris leaves are taller and thinner than bearded iris leaves. Japanese iris leaves have a distinct rib that runs lengthwise down the leaves. This rib is a good way to distinguish Japanese iris from other types of iris.
to white blue and shades of purple; the variation in shape is unmatched. These
delightful irises bloom after the tall bearded variety and extend the iris season into July
in the Northeast. Japanese iris have no beards and their iris leaves are taller and thinner than bearded iris leaves. Japanese iris leaves have a distinct rib that runs lengthwise down the leaves. This rib is a good way to distinguish Japanese iris from other types of iris.
WHEN TO PLANT: These irises can be transplanted almost any time from spring to late summer but shortly after the bloom period is best. This gives the new roots sufficient time to anchor the plant before winter freezes. Plants set out in the late summer need to be mulched to prevent heaving over winter.
LOCATION and WATER: They will do very well beside a stream or pond, but in cold climates they do not like to have their feet in water during winter. No other iris is influenced to as great a degree by culture as are Japanese irises. They require ample moisture, especially up to bloom time. You will be rewarded with much healthier plants and bloom if the plants are kept watered all summer long. Lack of moisture will stunt the plants and produce miniature blooms. These irises will grow and bloom best planted in full sun.
HOW TO PLANT: Do not let the roots dry out when planting! Plant rhizome 2 - 3 inches deep, depending on the heft of the soil. If planted in a depression of 3 - 4 inches, this will help to catch and hold moisture; since new roots form above the old roots. If you wish to maintain a clump in one spot more than 3 years, planting in a depression will permit the gradual filling of soil and help the plant's vigor for a longer period of time. After planting, keep well watered until plant is established. After 3 to 4 growing seasons, the new roots will be coming out right at the soil level and it will be time to divide the clump again. Best bloom is usually on 2 to 3 year old clumps.
SOIL: Japanese iris like a rich, heavy soil with lots of organic matter. If your soil is clay the addition of organic matter and some sand will help loosen it, If your soil is sandy, organic matter will help it retain moisture and add nutrients. Cow manure and peat moss work best. The soil should be slightly acid, with a pH between 5.0 and 6.5. Lime is fatal and also bone meal which releases lime as it decomposes
FEEDING: Japanese iris are heavy feeders. A liberal application of a balanced fertilizer like 12- 12-12 in the spring and just before bloom is beneficial. Weak plants showing light green foliage will be invigorated by a biweekly foliar drench application of Miracid. The preparation of your iris bed with composted manure and peat will be a good start for your JI, but once planted do not fertilize transplants until they have become established. (The same is true for Siberian Irises)
MULCH AND PESTS: We recommend heavy mulching year round for Japanese Irises, 2 - 3 inches. The mulch helps to conserve moisture, discourage weeds, and prevents heaving of fall transplants. Remove old foliage after the first frosts with a serrated knife. Destroy the old foliage, which may contain borer eggs or thrips. These two main pests of Japanese Irises can be controlled with systemic insecticides, such as Cygon-2E or Isotox./Orthene. Cygon is no longer sold, so when looking for a replacement, ask for a systemic poison. UNDER NO CIRCUMSTANCES do you exceed the manufacturer’s directions. These are strong chemicals and sometimes may be used at half strength.
CARE: These irises require ample moisture especially at bloom time. In the spring if rainfall is not sufficient, give extra water till bloom. The equivalent of one inch of rain per week is sufficient in most soils. Good culture increases height, branching, and size and quantity of bloom, After planting, a heavy mulch is helpful. Oat straw, oak leaves, or pine needles is recommended.
DIVISION: Japanese iris need to be divided every three to four years. A clump that has formed a solid ring with a bare center needs to be divided. After the plants have been divided, trim the leaves to a height of four to six inches. Replant the divisions in a depression and it is essential to keep the new divisions wet. JI can be divided in most any time during the growing season and right after bloom is a popular time. Spring is a good time in New England since it is easier to keep the divisions moist in the spring and the plants to be well rooted by the time winter sets in.
At the time of division, the iris should be moved to a new location where japanese iris have not grown before. It appears that JI excrete something into the soil that causes the iris to lose their vigor over time and decline. It is recommended that something other than iris be planted in the soil since other types of iris will grow there but not vigorously. The one exception to this is soil that has a lot of water leaching through it such as soil under a downspout or by the side of a stream. Whatever is causing the iris to lose vigor appears to be removed by water leaching. Research is ongoing in Japan to determine what is causing this effect. Japanese iris in Japan are commonly grown in pots and it is easier to replace the soil the iris grow in.
LOCATION and WATER: They will do very well beside a stream or pond, but in cold climates they do not like to have their feet in water during winter. No other iris is influenced to as great a degree by culture as are Japanese irises. They require ample moisture, especially up to bloom time. You will be rewarded with much healthier plants and bloom if the plants are kept watered all summer long. Lack of moisture will stunt the plants and produce miniature blooms. These irises will grow and bloom best planted in full sun.
HOW TO PLANT: Do not let the roots dry out when planting! Plant rhizome 2 - 3 inches deep, depending on the heft of the soil. If planted in a depression of 3 - 4 inches, this will help to catch and hold moisture; since new roots form above the old roots. If you wish to maintain a clump in one spot more than 3 years, planting in a depression will permit the gradual filling of soil and help the plant's vigor for a longer period of time. After planting, keep well watered until plant is established. After 3 to 4 growing seasons, the new roots will be coming out right at the soil level and it will be time to divide the clump again. Best bloom is usually on 2 to 3 year old clumps.
SOIL: Japanese iris like a rich, heavy soil with lots of organic matter. If your soil is clay the addition of organic matter and some sand will help loosen it, If your soil is sandy, organic matter will help it retain moisture and add nutrients. Cow manure and peat moss work best. The soil should be slightly acid, with a pH between 5.0 and 6.5. Lime is fatal and also bone meal which releases lime as it decomposes
FEEDING: Japanese iris are heavy feeders. A liberal application of a balanced fertilizer like 12- 12-12 in the spring and just before bloom is beneficial. Weak plants showing light green foliage will be invigorated by a biweekly foliar drench application of Miracid. The preparation of your iris bed with composted manure and peat will be a good start for your JI, but once planted do not fertilize transplants until they have become established. (The same is true for Siberian Irises)
MULCH AND PESTS: We recommend heavy mulching year round for Japanese Irises, 2 - 3 inches. The mulch helps to conserve moisture, discourage weeds, and prevents heaving of fall transplants. Remove old foliage after the first frosts with a serrated knife. Destroy the old foliage, which may contain borer eggs or thrips. These two main pests of Japanese Irises can be controlled with systemic insecticides, such as Cygon-2E or Isotox./Orthene. Cygon is no longer sold, so when looking for a replacement, ask for a systemic poison. UNDER NO CIRCUMSTANCES do you exceed the manufacturer’s directions. These are strong chemicals and sometimes may be used at half strength.
CARE: These irises require ample moisture especially at bloom time. In the spring if rainfall is not sufficient, give extra water till bloom. The equivalent of one inch of rain per week is sufficient in most soils. Good culture increases height, branching, and size and quantity of bloom, After planting, a heavy mulch is helpful. Oat straw, oak leaves, or pine needles is recommended.
DIVISION: Japanese iris need to be divided every three to four years. A clump that has formed a solid ring with a bare center needs to be divided. After the plants have been divided, trim the leaves to a height of four to six inches. Replant the divisions in a depression and it is essential to keep the new divisions wet. JI can be divided in most any time during the growing season and right after bloom is a popular time. Spring is a good time in New England since it is easier to keep the divisions moist in the spring and the plants to be well rooted by the time winter sets in.
At the time of division, the iris should be moved to a new location where japanese iris have not grown before. It appears that JI excrete something into the soil that causes the iris to lose their vigor over time and decline. It is recommended that something other than iris be planted in the soil since other types of iris will grow there but not vigorously. The one exception to this is soil that has a lot of water leaching through it such as soil under a downspout or by the side of a stream. Whatever is causing the iris to lose vigor appears to be removed by water leaching. Research is ongoing in Japan to determine what is causing this effect. Japanese iris in Japan are commonly grown in pots and it is easier to replace the soil the iris grow in.