This is my first year trying to create some bonsai trees, so I bought a few mugo pines, dug up a few small willow trees, and am even trying to grow some trees from seed!

I tried trimming up some of the trees I bought about 2 weeks ago and repotted them, using a mix of sand, vermiculite, peat moss and some bonsai soil. Several of them seem to be doing alright, but one of the mugos is turning almost completely brown...anything I can do? Should I try repotting it in regular potting soil?

I've got some pics up (including the dying tree) at:

http://www.brianandheather.info/bonsai/

I'd love any advice on anything (pictures being in focus will be a must for my next attempt).

I've been inspired by what I've seen here and am looking forward to trying this and hope not to kill too many trees in the process...

Thanks!!