Lift and divide perennials this month to thin out overcrowded clumps and keep your plants youthful and healthy. It's a great time of year to do it, as the plants are starting to slow down for winter so you won't check their growth by splitting them, and there's still warmth and moisture in the soil.
Most clump-forming perennials, like crocosmia, daylilies, epimediums and bergenia, get a little crowded after three or four years, gradually affecting the flower display. Most can be divided in early autumn, but there are some exceptions: irises and other spring-flowering plants like primula are best left till summer, after they've flowered.
Dig up the whole clump with a fork, taking care to damage the roots as little as possible. Shake off any excess soil, then start to split up the clump into several sections. Smaller plants can be pulled apart with your hands: larger ones such as daylilies need levering apart. Drive two garden forks back to back into the centre of the clump and work them apart, breaking up the clump as you do so.
You should get at least four smaller plants from each clump: plant straight away into fresh soil, and water them in well.