Pruning should be done any time between late autumn and late winter, as by then, the flowering season is over, and the climber has shed its leaves. It is easier to shear them when the plants are bare, as they allow a better idea of its trailing route.
Pruning Young Climbing Rose Plants
A couple of main strong vines should be trained out horizontally, to ensure that the shoots do not cross each other. The sprouts (shoots) coming from these vines are the flower producers. To facilitate speedy growth on the main branches (vines), tip-prune them till the first strong bud, to encourage new lateral shoots.
Around the same time, remove all dead, diseased or weak growth, and dead flower heads to encourage further flowering. One can also carry out this activity just before the flowering season starts.
However, this is done to clear the plants of any overgrowth, or entanglements. Do not crop close to the flowering bud sprouts. A young climber should be trimmed only to encourage growth, until well established.
Pruning Established Plants
Pruning is easier for established roses than young climbers. As their formative training is done, pruning is only done to further bushy and large flower growths. Once the flowering season is over, and the plant is bare, limit the rose vines (major ones) to about four or six, and spread them out on all sides.
Preferably keep the younger green ones, and remove the excess vines. Cut back the tips of these vines by a couple of inches. Unlike other roses, only the tips have to be trimmed for climbers, as it is unhealthy for the plant to have its main stems (down stems) severely cut back, and pruning back the long stems will alter the look and training of the climber.
Pruning will also depend on the two types; once flowering and repeat flowering climbers. Once flowering roses should be pruned immediately after the flowering season is over. As they mostly flower on the old wood, trim just about a quarter of the wood stems.
Trim repeat flowering climbers during its inactive period. Constantly keep cutting dead flower heads to encourage speedy re-flowering. Do this either in late winter or early spring, cut about one-third of the old wood veins, and trim the remaining to control its growth and shape.
This will help control the spread of plant diseases like mildew, black spot, etc. Spread a rose fertilizer over the soil and mulch them with layer of garden compost to encourage growth. Pruning will also encourage the growth of healthier stems and attractive large-sized roses.