Most rose pruning is done in the spring before blooms start to show. Watch the leaf buds on your rose. When they begin to swell and take on a pink or reddish hue, it's time to prune. Timing is critical, as it's best to prune the plant before the buds break open and right after hard frosts have ended in your region. However, certain roses are finicky about pruning time and prefer to be cut back before breaking dormancy.
Ramblers and climbing roses must be pruned to remove winter damage and dead wood and shaped to keep their size in check. Ramblers bloom only once and can be pruned right after flowering, all the way back to 2 to 3-inch canes if you wish. They quickly regrow, so don't worry, as you won't lose any flowers the following season.
The most obvious areas to prune on rose bushes are the dead, woody remains of flowering stalks. These dead canes may have snapped under the weight of snow or simply succumbed to a harsh winter. The less obvious canes to prune include those that are spindly or have shoots that extend well beyond your desired growing region. The ultimate goal is to maintain a "v" formation, or vase shape, between several, evenly spaced major canes that sprout from the ground.
In the spring, take inventory of your rose bush, noting its overall health and shape. Then go low, pruning off dead canes at the base and opening up the center of the plant to allow light and air circulation.
Follow old wood down the cane to a location that looks healthy (or green). Cut it at a 45-degree angle, taking care to expose the white flesh inside. If the flesh is not white, cut lower until you reach healthy flesh.
Remove canes that are thinner than a pencil. These canes will grow gangly and produce very little blooms.
A sucker is any new vertical growth that extends from the main canes. Suckers can also pop out of the ground. Suckers will contain no flowers at all or flowers that are inferior to those growing from grafted branches (canes that have fused together). Trim these at the ground or below the spot where the main branches fuse.
Prune new growth to shape the plant to your desired look. Make clean cuts at a 45-degree angle, about 1/4 inch above a bud that is facing toward the outside of the plant.
The proper pruning specifications vary depending on the type and classification of your rose bush. Make sure you understand the particularities of your rose's variety before you prune.
Modern roses like hybrid tea, grandiflora, and floribundas bloom best on the current season's growth. Prune hard in the spring (1/2 to 2/3 of the plant's height) and remove all old woody stems. Create an open vase shape with the remaining canes by removing the center stems and any crossing branches. Leave 3 to 5 healthy canes evenly spaced around the plant, cut at various lengths, to encourage continuous blooming.
Shrub rose bushes, like the Knockout varieties and "The Fairy," are repeat bloomers, flowering on mature—but not old—woody stems. Leave them unpruned to increase vigor in the first two years, and then remove 1/3 of the oldest canes, in addition to any dead, diseased, or dying canes.
Climbers, like the William Baffin rose, may repeat bloom, as well. Prune this bush early to remove winter damage and deadwood. Then, prune again after flowering to shape the bush and keep its size in check. Remove old and weakened long canes, as needed.
Hope this helps!