Japanese Iris

Japanese iris -Iris ensata- are beardless iris and are one of the last iris to bloom in the garden - about a month or so after the bearded iris and Siberians.

Quite a few folks have problems growing this plant so here’s the details of how to succeed.

As with growing any miffy plant, it is really knowing how to handle a few small details that will allow you to succeed.

Growing Japanese Iris

Full sun: There is little point in trying to grow Japanese iris in the shade as the blooms will become smaller and smaller. Given that this is one of the larger flowering of the iris family, you want the full sun.

Acid soils: I grow this plant in a 50:50 mix of garden soil and peat moss. I’ve even grown it in 100% peat when I grew it as a container plant sitting in the lip of a small pond.

Moisture levels: This is where most folks get bent out of shape and lose the plant. Japanese iris seem to do best in my garden when it is given very damp - almost swamp or shallow pond side planting until it blooms. After that, it wants consistent moisture but not swampy. When I grow this plant as a container plant, I let it be very wet until after blooming, then I take it out of the pond and put it into the garden or someplace where I can allow it to dry out those crowns for the rest of the summer. I’ve had no problems growing it in this way. If you grow Japanese iris in the garden, it wants a constant moisture - so you’ll have to water it regularly and mulch it to keep that moisture in the soil.

Feeding: These plants are very heavy feeders compared to other iris. Do give each plant several shovels of compost every spring and again just as it is throwing buds for best results. You can feed compost in the spring and a feed of liquid fish emulsion just before buds for excellent results as well.

Spacing: When happy, they expand fairly quickly so do plan on giving them 24-30 inches between plants.


Divide this plant in the very early spring or fall. It is easy to do with a shovel. Dig up a clump and cut or pry it apart. No big deal here.

You’ll want to divide your iris every 3-5 years because it will become overcrowded. If you see a dead center surrounded by tall leaves, it really is time to divide.

Replant the divisions by putting the roots 3-5 inches deep in a moist rich soil.


As you’re going to be mulching for moisture control, there’s little else you need to do.

Cut dead foliage back to the ground and discard it in the fall. This is largely to get rid of any thrip eggs that might be trying to overwinter in that foliage.

Potential Problems

There are reports that you should never plant a new Japanese iris in the same spot as a previous one occupied. Apparently some secretion in the soil from the previous plant’s roots kills off new plants. The solution to this is to either put your new iris in another spot or irrigate heavily to drive the secretion downward and out of the root zone (or both).

Thrips will lay eggs in buds and destroy blossoms.


If you get the soil right (acid) and the watering (constant) then growing Japanes Iris is easy. Get either of those wrong, and this plant will fade away slowly but surely in your garden.

Do you have a question about Japanese Iris?

Japanese Iris
Japanese Iris

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