Nico, It's refreshing to have one so interested in gardening. Sedums cover a large range of plant types. There are the creeping ones and the upright type. These are hardy succulents, propagation easily done by divisions and stem cuttings. Which kind do you have? The upright form of sedums like 'autumn joy' will die back to the ground every winter and regrow from the base. It can be divided to keep the growth in check. As for the creeping types, simply trim off the trailing stems to smaller size and it wouldn't matter how much to remove.

Sorry, I should have specified. I have an upright one and I've divided it last fall. It was so big last year it's stems fell over exposing the center of the plant. The divided ones are already pretty big (almost a foot in diameter). Since I read you can prune back an upright sedum to make a more compast plant, I thought I would try it this year. I'll probably try it on one plant and see how it differs from the other plants later this summer.

BTW - I am new to gardening and love it. I don't stop thinking about my garden (which is obviously in process) from April to June. I just wish I had more time to be in my gardens (having a two year old keeps me busy :o)

I have a 6 year old. She's been gardening with me since she was able to crawl and has caught the bug. I caught the bug when I was still very young and it's remarkable that to this day, I'm still hooked.

With regards to the sedum. I've never nipped off the sedum to make it more compact. For one thing, I don't want nip off it's buds. Pruning this way normally works with shrubs but not usually associated with this form. (the more you nip off the lead branch and more branches it produces). Now it is possible that by nipping off the stems, you will force the plant to produce more stem growth from it's base. So go ahead and experiment.

By the way, whatever you trim off, do not discard. Let it air out for an hour or 2, and stick it in soilless mix. That cutting will grow into sedums.