How do I divide bearded iris?
QA neighbour recommended that I lift and divide my bearded iris plants. How should I carry this out?
Maureen Clifford, Tunbridge Wells
A July is an excellent time of year for lifting and dividing rhizomatous bearded iris (Iris germanica), as rhizomes need sun and dry periods to ripen the root system, so they build up reserves for flowering next year. This group of iris is often referred to as flag irises.
Once flowering is over and when the rhizomes start to get old (normally after two or three years and when clumps become hollow in the centre), they’ll need lifting and dividing.
This process ensures that plants don’t become too crowded, and will help to keep them flowering in years to come. Put on strong gloves as the sap from iris can irritate skin. Using a fork, gently lift congested clumps from borders. Prise apart large clumps with your hands and remove excess soil to reveal the fleshy rhizomes. Take care not to damage them.
Each division will need leaves attached to a healthy rhizome and roots. Cut off any old or damaged sections of rhizome, leaving 4-6in (10-14cm pieces). Using secateurs, trim overly long roots.
Before re-planting, to stop the division rocking about in windy weather, and to reduce moisture loss, cut the leaves into a fan shape, roughly 6in (15cm) tall.
Finally, replant divisions at least 6in (15cm) apart, making sure the top half of the rhizomes are exposed to sunlight.
Keep plants well watered during the first season after division. If new roots dry out, plants may not establish and could take several years to flower well. This group of hardy iris needs a neutral to slightly alkaline soil that’s well drained and ideally in full sun. Flowering stems rise out of a fan of sword-like leaves that are produced at the end of the rhizome. After flowering, the leaves die back.
Short cultivars flower earlier in summer than tall ones. They have a brief flowering period, but rarely suffer from problems.
In autumn, remove any leaves that fall and congregate in clumps. If these remain in place over winter, they can become damp and cause rhizomes to rot.