What's the variety?

Something I wish I had known when I started with climbers is that almost all hardy, repeat blooming climbers come out of two lineages - AgCanada kordesii, or New Dawn. Neither of these produce roses that can read, or are remotely cooperative when it comes to training. I would *love* to see a pruning tutorial tackle New Dawn, but it isn't going to happen because the presenter doesn't want to end up having to be rescued by the cameraman. So I have never seen anything about training climbing roses that doesn't come out of some sort of alternate reality. My best guess is that the rose Paul Zimmerman is trying to train in this video, is some sort of Noisette, which is going to have a very different growth habit from what I'm used to.

To answer the question, of course you can cut them back, but there is a decent chance they will die off, or only produce very weak laterals.

Gallica, I have Florentina, Quick Silver, Generous Gardener, Mme Carriere, Dublin Bay, and Iceberg.

You want to limit horizontal growth, right? Train anything back as far as you want, then train new growth coming from the reduced canes in the direction you want as it extends and is the most flexible to cooperate. Do the training right away as it is putting on size early on from spring on. That way you have the growth growing in the direction that you want without having to force it as you would if you waited until it progressed to a hardening off stage later in the season. At that time getting it to cooperate if you want to change its direction may be problematic.

Moses

I have grown all the climbers you list and some of them are going to resist any attempts to keep them reined in. Even in what used to be my zone 5, my Mme. Alfred Carriere wanted to eat the south side of my house alive and bitterly resented any pruning by refusing to bloom on anything but old wood. Since she was marginally hardy in my zone, I only got blooms in one out of 5 year or so. In warmer zones she's happier and blooms longer, but also much huger.

If you are training a climber vertically only without any horizontal growth, you run the risk of the plant blooming only on the ends of the canes. With my climbers, in order to get more lush bloom you need to train smaller canes growing vertically from horizontally trained canes. Yes, those laterals then become "real" canes when you train them sideways and more laterals grow from them. In that case, all the rose canes ("real" and lateral) all bloom at the end of the canes but since you have a lot of new canes from the horizontal it looks like you have a full round of blooms.

If you're looking for a tall structure of a rose on your French Tree guards that has a small cluster of blooms at the top, then you can keep some of the other roses you mention more or less constrained on this structure. Dublin Bay and Quicksilver aren't huge climbers in my zone, and frankly both Iceberg climbing and Generous Gardener were weak growers and poor bloomers in my zone so they would barely climb here at all anyway. Florentina is very robust and a great bloomer when you train her horizontally, so I doubt it would last long on this structure, particularly straight upright.

What you could do if you want more blooms is train the rose to gradually spiral around those tree guards. A happy Florentina will swamp those 42" supports quickly however (any mood of MAC would swamp it even faster). I train my Florentina on 8 foot arches and it needs a pretty strong structure. Think mature canes with a diameter of a half dollar or so that get stiffer with time.

Just my two cents - you can always give it a try and add a more firm support over time. Just don't plant them somewhere that you'll be disappointed or skewered if they grow more than is feasible on that support after a few years. Most climbers take a good 4 years to grow anywhere near their mature height so don't just them to be tame by their performance in their first couple of years.

Cynthia