Dorset,
United Kingdom 
I have a large rhodedendrum plant in a tub which is now very overgrown. I have looked on the Internet and am told to do it in march. I had thought that this was the time of year to do it. Please would someone kindly give me some advice. I do not want to kill it!
It is in fact two plants. One red and one purple. This is an old plant which has been in this garden for some years. Sorry I did not make that clear. What I was asking was when should I cut it back? Now or in the spring?
25 Jul, 2012
Answers
Were you thinking of planting it out, or cutting it back, Complete Beginner? (sorry - nothing else to call you!) Rhodos flower on the previous year's growth, so if you cut back now, you may lose next year's flowers. I doubt very much that you will kill it, even with a heavy cut-back. If you want to plant it out, I agree with all that Taz advised.
25 Jul, 2012
I would have thought if it,s in a pot it is no different from buying one in a garden centre, a good soak before planting and if it,s going in the garden puddle the hole with water before planting,
. good luck
25 Jul, 2012