After flowering has finished this is the time to lift and divide the moist loving Iris sibirica and ensata clumps. Discard the central sparse sections.
Split the remaining clump into large sections. Replace the areas of the clump with plenty of shoots back into the soil with additional compost from the garden compost heap to replenish the nutrients recently used in flowering. Doing this now allows the plant to root down well and recover before Winter.
Do not divide every clump of Iris in the same year so that you have a rotation system going on.
Pond Iris sat in the water on a shelf also need dividing once they have flowered - same principles apply - do some every year in a 3 year rotation system. The benefit of leaving some emergent pond Iris untouched is that some will continue to be of value to dragonfly and damselfly larvae to use to climb up when they are emerging from the pond to become adults. Those divided and repotted will be cut down in height so that they will re-establish more quickly.
If the water Iris in a container pond has outgrown the basket it can be divided in the same way and either some older sections discarded or a second basket made to sit in another position in the support grid.
For more details on how to divide a Water Iris please see our Tips and Advice page.