When to Divide Japanese Iris?

Japanese iris is a truly beautiful ornamental flower. Though similar in look and color to the more common version of iris, there are some key differences that make caring for them a little different. Many of the tasks will be similar in fashion to regular irises, but the timing will be different due to differences in growing cycles between Japanese varieties and other irises. Knowing when to divide and plant Japanese iris will allow you to successfully keep these gorgeous flowers in your yard for many years.

For all irises--Japanese or otherwise--dividing is going to be a critical factor for long-term plant health and vitality. Dividing the plants stimulates new growth and can bring to life plants that seemed to be dwindling a bit. Sandra Mason, a horticulturist and environment educator at the University of Illinois, points out that low flower production is a telltale sign that division is needed. Water Gardens Information adds that a dead center is another key indicator. Japanese irises are similar to their relatives in that division is usually necessary once ever three to five years. They differ in that the best time to divide them is unique from the rest of the family.

Gardeners with experience growing the traditional species of irises are usually accustomed to dividing the plant from mid-July to September, according to Mason. The summer heat really helps them get established before the first frosts of late autumn or early winter. Though Japanese irises are not particularly fussy, the best time to divide and plant them is early spring. The Canadian Iris Society has said that, "Early spring to right after bloom is the best time for us," adding that hotter climates further south may be able to achieve good results dividing in the fall. Consideration of your particular climate is important primarily because you want your iris to be able to establish a strong root system before going dormant in the winter. This will set the stage for a more glorious display the following year as the plant can concentrate its spring energies on upward growth and flowering (as opposed to downward root formation).

As with regular irises, division of the Japanese iris is simple: Cut through the rhizomes, then plant them. The division process is a great time to inspect the root systems for any problems, such as disease, rot or insect damage. Recognizing any of these signs in the roots can help you get the jump on any potential problems for your irises in the future, according to Mason. Once you've planted your newly divided Japanese iris, water regularly for two to three weeks and give a dose of fertilizer every two weeks to help the plants re-establish themselves. This will drastically effect the overall success of the division process.

Most irises are particularly hardy, easy maintenance flowers. Japanese iris is not much different; in fact, if you have grown irises before you should have no trouble growing Japanese iris. Mentally adjust your timetable, dividing in early spring as opposed to the usual mid- to late-summer division dates for your regular irises, and you should be just fine. The unique look and vibrant growth of these plants will guarantee that your efforts are rewarded.