It depends on how they're grown, whether they're long-caned or bushy, and how much they repeat. Pegged long-caned Bourbons tend to exhaust their canes after a year or two -- I've found that new canes that shot up after last year's first flush will be the best bloom-producers when pegged for the first flush of their second year, but are more meager during the first flush of their third year, after which I remove them. The ones that don't repeat much do better by doing just a light trim in Spring, keeping as much of last year's new wood, then cutting back harder after the first flush. Bourbons like 'Souvenir de la Malmaison' would probably do best by starting with typical HT pruning, but not cutting back as short, and not reducing to so few canes. Basically, first remove anything dead, damaged, diseased, or going the wrong way. Then look for where two canes are competing for the same space, and remove the less-vigorous of the two. Once you're down to your healthy strong canes, trim bloom-laterals down to four or so buds, and trim back main canes to the highest strong bloom-lateral, or the highest strong bud going in the direction you prefer. Other Bourbons that are more arching but not necessarily long-caned climbers can be scaled back to a sort of high-centered inverted traffic cone shape -- outer canes shorter and extending outward, with center canes left a bit longer and going up. Of course, this would be after removing dead, diseased, damaged, or crossing canes.
:-)
~Christopher
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Pruning
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