|Their radiant beauty has a bit of a downside. They need a certain amount of attention. They have one serious pest the Iris borer and they outgrow their space fairly quickly. This growth necessitates regular digging and Iris dividing.
How Often Must I Dig Them? Depending on their size, from the miniatures through to the majestic Tall Bearded, digging and dividing needs to take place every 3 - 7 years. There is no hard and fast rule as to how often this propagation process needs to happen. In the smaller varieties, it is usually a matter of them outgrowing their allotted space. The larger varieties will just develop an older less viable mass of rhizomes, (they are the fat horizontal stems at the surface of the soil,) in a large centre section. All of the blooming bits will be on a the edges of this mass. Now it is the time for Iris dividing.
When Do I Do This? Mid summer, when other garden chores are at a minimum, is the perfect time for Iris dividing. Late July through early August sees me in the garden, with a fork, searching for aging Iris.
How Do I Do It? Using a strong garden fork to reduce the amount of soil you dig up; remove the whole clump from the ground and knock off as much soil as possible . Cut the leaves to less then half of their length, leaving a stiff fan of healthy green. With your fingers or a strong hand cultivator, separate the multiple rhizomes so that you have several separate sections (2 - 6 cm long) of healthy rhizome with one or two fans of leaves at the end. Your clump should yield several of these. Throw away the large central mass of rhizomes. Your good pieces should have several white fleshy roots hanging from the bottom. Trim these roots about 10 cm long.
Do I Replant These Fans? Yes. Dig a hole deep enough to let the fleshy roots hang straight down, leaving the top of the fat rhizomes about 2 -3 cm below the surface of the soil. Add some good compost to the soil and then work it back into the hole so that the roots are spread out and in good contact with the soil. Continue to fill the hole and gently firm the soil until the entire rhizome is buried that 2 - 3 cm. The fan of leaves should now be standing erect in the garden ready to start growing.
Is That It? No! Make a raised ring of soil around the rhizome so that you can add a significant amount of water to your transplant without it running away. I use a high phosphorous transplanting fertilizer for this initial watering, to induce new root growth. Now you are an expert at Iris dividing.
The added bonus here is that you have several extra fans of your favourite Iris which you can plant in other areas of your garden or you can make great gardening friends by giving them a piece for their garden. Just don`t be upset when they win Best Iris at next years flower show, using the great variety you gave them. That’s just part of the joy of Iris dividing.
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