The better graded roses have more healthy canes to start out with. To be grade #1 I believe they have to have at least 3 canes. I've gotten some with as many as 6 healthy canes on them. A bigger plant with more canes always stands a better chance of making a nice healthy bush shape and probably has better chances of surviving my winters here.

The hard part is there are quite a few roses which will simply NOT generate Grade 1 plants. There are even more which don't generate a high percentage of Grade 1's.

In a cold weather climate with a short growing season, you may need a variety vigorous enough to produce a large percentage of grade 1 plants--otherwise it may not grow fast enough to recover from winter each year. I get one more bloom cycle than Seil, even though we are in the same zone. This allows me to propagate HTs via cuttings despite subzero winters.

From what I've read, smaller plants are often the result of plants getting less water. In my yard, small plants usually result from issues with tree roots and inadequate light.

Oh this is great information! Thank you for asking this. I Have been wondering this as well.