The larger the root mass, the better chance of survival and the better chance of having a more vigorous rose in the long run ... I am talking about own root plants. Since you are planting a larger plant, you have more foliage for photosynthesis for the plant to create food and the larger root mass allows the plant to take up moisture and nutrients better than a smaller root mass. This means that the rose has more tools to become a healthy rose when it is finally put into the ground.
That's the theory. Some people say they plant their bands directly in the ground and the roses are just fine. I know that if I took that approach in this garden, I'd have dead roses in no time.
It gets too hot here, too, to deal with plants in small containers ... and too cold. That's why Kim and I agreed that he would grow them up to the three gallon can size before he delivered them and because he could only come up in November, I arranged to have them over wintered in a friend's greenhouse. I felt that November was just too late for me to plant anything.
In my climate and my soil, I don't want to plant anything smaller than a three gallon can. People in milder climates don't have to be quite so rigid, but my sense of things is that I still would want a larger root mass than you can get in a one gallon can.
One of my rose friends that lives in Camarillo, located on the coast in central California, and won't put a rose into the ground until she sees roots coming out of the bottom of a five gallon can. Of course, she doesn't have to deal with the high temps that are common for me so it is easier for her to maintain her roses in containers.
For budded roses, you already have rose with a larger and more mature root mass than you would have for an own root plant potted up to a gallon can, so planting them in fall makes sense, but the plant still has to grow feeder roots so it can take up moisture because most of those roots are lost when the plant is prepared for shipping.
I can't even begin to tell you, if it is OK to plant a budded plant in November because I don't know your climate. I know that I would be hesitant to plant that late in my climate and I am in a slightly warmer zone than what you show for your garden. Mountain weather is always unpredictable. Also, once the night temps drop below freezing, I put away my hoses and the roses are on their own.
I don't know if anything I have said in this post even begins to answer your questions.
Smiles,
Lyn
