I have a bunch of new bare-root roses coming from mail order that I am
going to plant around my patio, and was looking for suggestions for
the most effective soil amendments.

Last year I planted my first rose bushes (I am a rookie) with a mix of
dehydrated cow manure and peat moss. It took about 1 - 2 months
before the plants started to grow, and I was concerned that the cow
manure was too high in nitrogen and perhaps was stunting/slowing the
roses' growth.

Any good recommendations?