I cut off flower stalks as the flowers fade then leave the plants to die back naturally as, with careful watering, the foliage can look good for several more weeks. Once it does all die down I remove it to make sure there is less shelter and food for slugs and then the pots go into a quiet corner to protect them from frost.
Come spring, I feed and water the minute I see the pointed buds appearing and that's also the moment to lift and divide if they need it.