QUESTION:

When should I prune my climbing roses?

ANSWER:

Climbing roses should only be pruned to keep them in bounds and to remove old canes.  Most climbers bloom on old wood, so cutting out last season's growth will cut back flowering canes.  You can head them back to keep them in bounds and remove one or two old canes. You can renew an old rose by cutting it way back but you will sacrifice flowers for the year. Pruning should be finished as the rose starts to flush with leaves. 

Training climbing roses laterally will force more blooming stems to shoot up. If you just let the rose climb straight up, the side shoots are not as thick.  This promotes more blossoming stems along the main branch then if they grow straight up.