T-ra,

The choice is yours whether to cut back Sedum or leave it stand. If you have stems that are sturdy, and can withstand strong winds and the weight of winter snow, you might like to leave them for winter interest. (My favorite sturdy-stemmed Sedum is 'Matrona'). On the other hand, if they flop from the middle, you should probably cut them back, since the stems will turn mushy as they lay on the ground. I cut some of my floppy ones back to 4-6". In the Spring, the spent stems will pull out easily from the main clump.

How often to divide depends on the size of the clump. Some varieties stay small, and you can leave them alone for a few years. Other fast growing types, like 'Autumn Joy' may have to be divided every two or three years, depending on the richness or poorness of your soil. You can slice right through the middle with a shovel/spade, or divide into quarters, or smaller divisions, but make sure each division has a good set of roots attached.

One more thing to consider (if you leave Sedums stand over winter) is that they tend to reseed quite readily. You may or may not want that. My gardens are getting somewhat crowded, so I don't like to see baby Sedums all over the place, unless I can give them away!

Hope all that info helps.

Julie