Q. How do I grow Japanese iris?
Japanese iris are among the showiest and easiest irises to grow. These beardless beauties are close relatives of American Iris versicolor and Iris virginica and of the yellow flag iris (Iris pseudacorus) of Europe, North Africa, and western Asia.
When planting Japanese iris, use strong divisions of two to three fans each. Small divisions take longer to get started and are more subject to loss. The roots should not be allowed to dry out during transplanting. Soaking the rhizomes and roots in water overnight before transplanting is beneficial. The rhizome should be planted 1-3 inches deep. A deeper depression will help to catch and hold more moisture. Japanese iris tolerates moist soils better than bearded iris. Since new roots form above the old roots, planting in a depression also permits the gradual filling in of more soil and compost, helping to maintain the plant's vigor for a longer period of time.
After planting, keep the soil moist until the plant is established. In the spring, if rainfall is not sufficient, give extra water until the plant flowers. Japanese iris can be planted almost any time from spring until fall; shortly after bloom period is probably best because it gives the plants sufficient time to establish new roots for good bloom next season. Of course, in very hot areas, transplanting should be done in cooler months.
Depending on what is available, till in an ample amount of composted manure and/or compost.The soil pH should be acid, ideally between 5.0 to 6.5. There is evidence that Japanese iris will tolerate a wider pH range, but growth and bloom will not be as good. If the pH is too high, the leaves will yellow. To lower the pH, add ferrous sulfate or agricultural sulfur.
After planting, a heavy mulch of 2-3 inches is beneficial. Oat straw is recommended. The mulch helps to conserve moisture as well as reduce weeds. If plants are set out in the fall, a mulch is needed to prevent heaving over the winter.
For tips on a variety of gardening topics, see our Plant Information Guides.
- Courtesy of NYBG Plant Information Service
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