I wouldn't use a fertilizer. What you really want is root growth not a lot of top growth. I would use a rooting hormone instead. There are powders, liquids and gel types. Be careful though. You don't want to use too much of that either. Most important thing is to keep that pot root ball whole when you plant it. The less you disturb the roots the better for the rose. Just dig your hole, slip the rose out of the pot and into the hole and back fill.