You know it’s time to divide and thin your iris when the clumps are crowded and the blooms are declining in numbers. There are many opinions on the best time of year for tackling this task and this mostly depends on where you live. As long as there are a good 4 weeks before the first freeze and you are able to provide adequate moisture, the iris will thank you with prolific blooms next spring. So go ahead and get started.
1. Lift the iris out of the ground. I prefer to use a garden fork, lift the whole clump, shake of the soil, and transfer the clumps to a wheelbarrow, one variety at a time.
2. Sort and trim. Toss all ‘mothers’ and tiny rhizomes. Keep only healthy looking plants and cut back foliage and roots.
3. Replant. If desired or needed, amend the soil for good drainage, then plant and water the iris in well. I recommend planting with the rhizome set into the ground and covered. If you live in a hot and wet climate, you may want to plant them a bit more shallow for better drainage.