Posted: 21/07/2013 at 17:32
I've been growing roses on & off for over 50 years and as long as you don't break up the root ball I would say dig a hole a bit bigger and deeper than the whole bucket, add some John Innes No 3 to the hole to raise the level so that when you sit the rose in the hole the height will be right. Mix a little Fish, Blood & Bone to the No 3 mix,(just a small handful), and if a rose has grown in that spot previously add a little mycorrhizal fungi ('Rootgrow' - available from most Garden Centres), make sure the rose in the bucket has been well watered then carefully remove it and plant in the hole without disturbing the rootball (or as little as possible). Backfill the hole with John Innes No 3 and gently heel in all around the plant to firm it in, then give it about a gallon (5 litres) of water.
I would recommend you wait until the present hot spell has subsided though, as no plant will relish being disturbed in this hot weather.
I just re-read your original post & realised you said you had it in a pot about the size of a bucket. I then got to thinking about the shape of the pot and how easy it would be to remove the rose from it if the top turned inwards. I was glad then to see a pic of the rose in its pot (it's beautiful isn't it). It will drop out of there with ease and very little disturbance to the rootball so you should be fine with it.