Hi Alex
In general, in our climate it is important to remove the flowers as soon as they go over as the corolla tube becomes damp as it dies which is a primary source of damp getting into the centre of the rosettes thereby leading to damping, rot and if not checked, death. In practice the ease of removing flowers varies considerably from species/hybrid to species/hybrid. Some such as Monika can be removed in bunches, its possible to strip a 30cm plant in less than an hour. With others however like afghanica you need to be very delicate and pull the flowers very gently (with tweezers usually) or you risk pulling the centre out of the rosette. Others have very brittle tubes which can break no matter how gentle you are. In such cases don't leave the base of the tube on the plant as this is enough to lead to rot. You need to pull the last few millimetres out of the rosette. Experience will give you greater ability to know which plants need more delicate treatment. Obviously people who try and set seed have to leave some flowers on in which case its safer to leave them nearer the edge so that if the rosette starts to rot, removing it might not be such an issue. Growers with a more continental climate are on the whole better able to leave flowers in situ as the drier atmosphere is less likely to lead to problems.
Paul
