Lifting and dividing irises

About irises

Irises can look wonderful in early summer, with masses of colourful blooms held on stout flower stalks. However, after several years the clumps will run out of steam and die off in the middle, leaving plants that are reluctant to flower. Fortunately it's easy to revive them.

How lifting and dividing works

Irises spread by underground rhizomes, a storage organ similar to a bulb. Plants can be split apart and replanted in the autumn or spring. It should be done every three to five years, depending on how many flowers the plants produce.

How to do it

• Ease a fork under the clump and lever it up carefully, making sure you keep as much of the rootball as possible. Put it on a bare patch in the border or place onto a plastic sheet on the grass - this will prevent your turf from being damaged.
• Using secateurs, cut the leaves in half horizontally. This reduces stress from water shortage after replanting and stops the plants from being blown loose in the wind. Next, split the clump into individual pieces making sure that each piece of rhizome has a few roots attached.
• You may be able to simply pull plants apart, but if the roots are tough use a knife or even a spade. Discard very old, unproductive pieces of rhizome at the heart of the clump.
• Replant irises in groups about 30cm (1ft) apart, with the rhizome just below the surface. Firm soil around roots and water well.

Other plants to divide

• The same technique can be used on other perennials that spread by rhizomes eg Veratrum and Libertia.

Aftercare

• Keep plants well watered until established and they should flower again within two years.

Five to try

• 'Broadleigh Rose' - pink flowers in late spring
• Iris chrysographes - fragrant, near black flowers
• 'Harvest King' - lacy, golden brown blooms
• 'Codicil' - powder blue flowers
• 'Top Gun' - two tone, creamy pink and orange