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Irises can be kept healthy and full of flowers by dividing clumps before they get congested. This is also a good way to increase stocks of plants.
Iris flowering the year after division. Credit: Ali Cundy/RHS Herbarium.
Both clump forming irises and those with rhizomes (fleshy stems at soil level) can be divided. Irises that are grown from bulbs are not suitable for division.
Bearded irises (sometimes sold as Iris germanica cultivars) have large fleshy stems (rhizomes) at soil level and flowers with soft hairs (the ‘beard’) on their lower petals (falls).
Siberian irises are clump-forming irises with beardless flowers. Large clumps can be divided to rejuvenate them if flowering has become reduced at the centre of the clump.
Iris unguicularis are low-growing clump-forming irises with beardless flowers that flower in late winter and early spring. Large clumps can be divided to rejuvenate them if flowering has become reduced at the centre of the clump.
Pacific coast irises are low-growing clump forming irises with beardless flowers and grass-like leaves. Large clumps can be divided to rejuvenate them if flowering has become reduced at the centre of the clump.
Irises for dry soils (bearded iris)Irises for moist soils (beardless iris)Perennials: dividingRHS video: Dividing irises
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