Late July and early august is the best time to divide bearded Iris, the type of Iris with fleshy rhizomes that lay on the surface of the soil. They should be divided every three to five years to stop rhizome colonies getting too congested, also giving you the perfect opportunity to multiply the plants in your borders.
Doing this task in mid to late summer, or about six weeks after the irises have finished flowering, gives the plants enough time to settle back into their new planting locations before the weather turns cold. The process is quite straight forward, but there are a few points to remember, which we have outlined in this step-by-step blog:
Lift large colonies of Iris rhizomes from your borders
At the right time of year, lift congested clumps of bearded Iris with a fork, which decreases the chances of root damage during the process. You may want to use the fork to loosen the roots around the clump first. Once you have lifted a clump, move it to a surface to work and divide the rhizomes by hand.
You should be able to ease the rhizomes away from each other quite easily, but sometimes you might have to apply a bit of force. The roots should stay attached to the rhizomes, but if any get broken, just cut them off as they will simply rot under the soil.
Give the leaves a chop
Like other divided plants, it is best to cut the foliage down at this stage so that autumn and winter wind doesn’t rock the plants, and the roots continue to establish well. The plant will produce fresh leaves in the spring, so don’t worry about damaging the plant by doing this step. Cut the leaves at an angle so that rain doesn’t sit on the leaves and lead to rot.
Plant the individual rhizomes into their new planting positions
Once you have divided all the rhizomes and cut down the foliage, you can replant them in their desired position. Just make sure that the rhizomes sit above the soil surface and that they face the direction of the sun, so that they can bake during hot days in late summer and autumn.
Water in well
To help aid plant establishment, be sure to water your divided rhizomes well, especially in hot dry weather when the soil is parched. Watering first thing in the morning or in the evening means water is less likely to evaporate before it has been absorbed into the soil.