Always did a dollar sized hole for a 25-cent plant. The bigger the hole, the looser the soil will be and the easier those tiny feeder roots will grow quickly. I can’t emphasize this enough. And never, ever (with a bare root plant) cut off healthy roots. You can remove broken roots but leave every healthy one that’s on the plant. They’re your ticket to early blooms.
When you backfill the planting hole, I always add one shovel of peat and one shovel of compost for every three shovels of soil. This gives the rose some quick nourishment and makes a wonderful soil for expansion. The only exception to this is if you’re planting in a clay soil and then I only add the compost. I do not add the peat as I want the rose roots to grow out into the soil that surrounds the planting hole. They might establish faster in peat-amended soil but they’ll grow better and survive longer in compost-amended soil.
The depth of the bud union (the swollen part where the roots meet the good top rose) is conventionally 2-inches below ground in North America. In northern sections, gardeners have started planting this 6-inches below the ground to protect it during harsh winters.
After the rose has been installed in the hole, backfilled and the ground thoroughly pushed down around the plant, I always turn on the hose to thoroughly wet down the ground. After the ground is muddy, I leave the hose to trickle for a half hour or so to really soak the ground.
After that, I just wait for blooms and their delightful fragrance.