How to Grow and Care for Japanese Iris

Japanese irises have the largest flowers of all irises, some measuring six inches or more across, and they are one of the last irises to bloom. The flowers are rather flat, rising above green blade-like foliage.

The plants like to grow around water during the spring and summer, which makes them ideal for spots where water collects and the soil remains soggy. Japanese irises thrive where other plants would fail miserably. The rhizomes are planted in early fall.

Note that Japanese irises are toxic to people and pets.

Japanese Iris Care

Japanese iris is a bit fussy with its growing requirements. They are not as easy to grow as many other types of irises. Here are the main care requirements for growing a Japanese iris:

• Plant the rhizomes in a location with full sun and loose, well-drained, acidic soil.
• Make sure it receives a lot of water in the spring, a little less in the summer, and only a moderate amount in fall and winter.
• Apply a high-nitrogen fertilizer twice in the growing season.

Light

This perennial performs best in full sun. At the upper end of its zone range, it benefits from some afternoon shade to shield it from extreme heat.

Soil

Japanese iris requires friable, loamy soil that is slightly acidic (5.5 to 6.5). Dense, compacted soil is not suitable.

Water

Japanese irises require more water than many landscape plants. They needs a lot of water in the spring when the plant is growing and less in the summer, though their soil shouldn't dry out completely. They need even less in the fall and winter, when excess water is harmful.

Temperature and Humidity

This iris is cold-hardy and it tolerates a wide range of temperatures, even deep freezes. Japanese irises thrive in humid conditions and don't do well in hot, arid climates.

Fertilizer

Established Japanese irises are heavy feeders though you should never fertilize new transplants. Apply a fertilizer high in nitrogen in the early spring and once more just after the bloom.

Types of Japanese Iris

Japanese irises come in different flower shapes (single, double, or peony-shaped), sizes, and color shades. Here are popular choices:

• I. ensata 'Variegata': Green and cream, vertically variegated leaf blades and large violet-purple flowers.
• I. ensata 'Japanese Pinwheel': Varying shades of flared purple or wine-red petals with thin white rims.
• I. ensata 'Sugar Dome': Delicate double purple-blue flowers with white veins.
• I. ensata 'Geisha Girl': Lavender flowers mottled with lavender-purple flowers.
• I. ensata 'Dinner Plate': A trademarked series of cultivars with extra-large ruffled layers of petals of either white, purple-white, purple-pink, or purple-blue combinations.

Pruning

Cut back the flower stalks after the bloom to prevent the plant from wasting energy on seed production.

Seeds?

Most Japanese irises sold in the nursery trade are hybrids, so the seeds won't produce plants that are true to the parent.

Propagating Japanese Iris

Japanese irises are propagated by division (except trademarked varieties, which may not be propagated). Dividing the clumps every few years prevents overcrowding, which decreases their ability to bloom. The best time to divide Japanese irises is in spring or fall. Here's how:

1. Dig up the entire clump with a spade or a pitchfork.
2. Wash the soil off with a hose or place the clump in a pail with water and soak it overnight. The next day, drain it.
3. Divide the clump into individual plants by hand or with a sharp serrated knife.
4. Cut off any of the old roots, which are long and dark as opposed to the new, white roots.
5. If dividing in the fall, trim the foliage to about five inches above the root system.
6. Replant the sections in new places at the same depth as the original plant.
7. Water the newly planted irises generously and keep them evenly moist.
   

Potting and Repotting Japanese Iris

Japanese iris lends itself to being grown in pots. This allows you to place it in standing water, such as along the edge of a pond, during the spring and summer when the water needs are high, then move it to a drier location in the fall and winter when the plant is sensitive to excess moisture.

Shallow and wide plastic pots with good drainage make ideal containers for Japanese iris plants in standing water. Use high-quality, humus-rich potting soil.

Repotting to a large container with fresh potting soil or dividing the plant becomes necessary when the rhizomes have reached the sides of the container.

Overwintering

When planted in garden soil, Japanese iris does not need winter protection. Container plants, on the other hand, require winterization to insulate the roots from the cold. In the fall, bury the pot in a location away from wet areas in your yard and dig it out again in the spring.

Common Pests

Japanese irises are vulnerable to pests such as snails and slugs. Aphids and iris borers are also attracted to this flower. Pesticides and insecticidal soap will help control these pests. Japanese irises are not frequently browsed by deer.

How to Get Japanese Iris to Bloom

Bloom Months

Japanese iris blooms between early June and mid-July.

How Long Does Japanese Iris Bloom?

The bloom lasts about two weeks.

What Do Japanese Iris Flowers Look and Smell Like?

Japanese irises have a distinct flattened appearance compared to other irises. The three petals of the standard are considerably shorter.

Three large petals fall around the standard. What also distinguishes Japanese iris from other irises is the size of their flowers, ranging from 3 to 6 inches in diameter. The flowers have a subtle sweet fragrance similar to violets.

How to Encourage More Blooms

For a full bloom, make sure the plants are getting enough sun and that they are not overcrowded, which also decreases their ability to bloom.

Caring for Japanese Iris After It Blooms

After the bloom, remove the stalks with the spent flowers. This deadlheading prevents the plant from developing seeds.

Common Problems With Japanese Iris

Faded Colors

Usually, the Japanese iris boasts deep colors. Fading colors occur after transplanting or due to extreme temperature changes.

Exposed rhizomes after a critter has dug the soil around the plants is another possible explanation for fading colors. After a few seasons, the fading of the flowers may also be a sign that it's time to rejuvenate the plant by dividing it.

Slow Growth

If the rhizomes have been planted too deeply, their growth as well as flowering may be stunted and poor. Check the planting depth and replant them shallower, one to two inches deep.

Mushy or Rotted Rhizomes

Too much water in the fall and winter, especially in combination with compacted soil, causes the rhizomes to get mushy or rot. They will fail to bloom at all. Dig up the rhizomes, cut away any affected ones, and amend the soil to improve drainage.

From: thespruce