Roses grow very well in containers, but after a few years they need to be repotted into a slightly larger container. It is usually recommended that roses be repotted during winter or early spring while they are still dormant. If you are transplanting during the growing season when the rose is actively growing, it is recommended that you cut them back to about half of their size. This is necessary because roses usually suffer transplant shock and removing their top growth puts less stress on them when recovering from being transplanted. None of this is necessary if you use this method to pot a container grown rose plant. You can transplant at any time of year and your rose plant will suffer very little, if any, transplant shock.
Select a new pot that is about 1 to 2 inches larger than the pot your rose is currently growing in.
Place a 1- to 2-inch layer of gravel in the bottom of the pot. Add about 2 inches of regular potting soil to the bottom of the pot. Add 1/4 cup of slow release granulated rose fertilizer to the soil in the bottom of the pot.
Put the rose, still in its old pot, in the new pot on top of the 2-inch layer of potting soil. Add more soil to the gap between the old pot and the new pot. Use a large dowel or small scrap piece of lumber to tamp down the soil in the small area between the old pot and the new pot.
Remove the rose, still in its old pot, from the new pot. You will be left with a hole exactly the size of the rose's root ball in the rose's new pot.
Carefully remove the rose from its old pot and slip the root ball into the prepared hole in the new pot. Firm the soil around the root ball. Add additional soil, if necessary, so the root ball fits snugly into the prepared hole.
Water until it drains out of the bottom of the pot.
Keep the rose in light shade---under a shade tree---for about 1 week until it fully recovers from transplanting, then move back into full sun.