Over the past 25 years I've planted over 300 roses by digging holes about 15" deep x 15" wide. If the native soil is of high quality (dark and loamy), then I only replace one-third of it with equal parts composted (rotted) cow manure and peat moss, to help with aeration and reduce compaction. If the soil is of poor quality, then I'll replace two-thirds of it with equal parts manure and peat - a ratio I learned many years ago at a course on soil science at the New York Botanical Gardens. I also thoroughly mix RoseTone organic fertilizer with the soil before filling in the hole. This has generally worked well for me across two different homes and gardens, as you can see by the 400+ photos of my roses in the NGA database, some of which can also be viewed here:
https://lens-work.com/public_h...
and also here:
https://www.fleischmannhouse.c...
