Experts and BHG readers answer.
Pruning Climbing Roses.
"It's a little late now to prune climbing roses. Climbers are best pruned early in the season (Late winter or very early spring when the new buds have just begun to swell.) You can prune again after they bloom to shape the plant and keep out-of-control canes in check.
Pruning in the fall just encourages new growth which is young and tender and easily frozen in an Indiana winter.
More important than pruning for great climbers like Altissimo is proper training. (Don't prune climbers for the first two years anyway.) Tie the flexible canes to their support or a wall or fence and let the red-blooming riot begin!"