Please tell us where you are located so we can give you specific advice for your conditions.

Generally you would only prune off 1/3 of the oldest canes in any one season to rejuvenate an old climber. I would not suggest taking off all of the canes. I lost a climber by doing that once. But I'm in a cold climate and the rose couldn't come back from both the winter and the severe pruning.

I live in Israel. A cold winter day is 15 celsius (59 F), a normal one is 18 celsius (65 F). The weather starts to get warmer in march. You can see more here: http://www.inisrael.com/tour/weather/ (i'm in the Tel-Aviv area)

I really don't like how the old canes grew (basically up). If I can prune at the base and star over, that would be my choice. Otherwise, what alternatives can you suggest?

Thanks,
Ittay

I'm wondering if it would be fine to prune them all back to about 9 inches as you might do for transplanting?
I shouldn't kill them but would give the opportunity to train the new growth.
Does this make sense? :)

Since you're in a warm climate you could prune it way back at any time. I still think I'd only take off some of the canes at one time and let them grow out and see what they do. Then you can take off some more and train as they grow. My thoughts though are that you're asking for the rose to grow in a way that it just isn't designed to do. Climbers climb. They put out long canes that go up and then will produce some laterals at the top to bloom on. If you want something to spread out you'd be better off with something that would ramble and spread or something that has a more mounding habit. There are some varieties that will have a bushier habit naturally and you may want that instead. I don't think that is Don Juan's natural growth habit. He likes to go straight up!

Thank you seil.

What I'm looking is something that will cover the pillar and will flower all along it. Is the Don Juan good for this or can you recommend something else?

I don't know if you are familiar with the rose data base site called Help Me Find dot com slash roses or not but you can look up all manner of roses on there. I've added a link for Don Juan so you can see some pictures of how it grows. Take note of where the gardens are located so you can see how it will be in similar conditions to yours.

Here is a link that might be useful: Don Juan at HMF

I have a Don Juan on an arch. I am in Southern California and my plant is old.

It blooms great in heat, but mine only gets about 8 feet tall and puts out pretty much straight rather stiff growth. I am not sure I would be able to wrap it around a pillar unless it was a rather large pillar. Everyone that visits leaves chanting Don Juan to remember the name because they like it, but I think I would not pick it for wrapping like you are planning. Mine seems to love some pruning so trying the one cane at a time might give you an idea if it will work or if you need a different rose for the purpose