Rules for rose pruning are closely associated with the type of rose being pruned. There are many varieties of roses and the classification of roses can be confusing. The American Rose Society divides all roses into three basic types: Species Roses which include all wild roses, Old Garden Roses which existed before 1867, and Modern Roses that came into being after 1867. Within these last two groups there are various classes. Modern Roses have 13 classes and Old Garden Roses have 22.
Here are some basic guidelines for pruning your roses. As a general rule of thumb, roses that flower only once in a season should be pruned right after flowering and roses that flower several times during the season should be pruned in late March or early April once the buds start to break (swell and green up): the adage is to prune your roses "when the forsythia blooms". Once-blooming roses flower on old wood and continuous-blooming roses flower on new wood. Most Old Garden Roses flower only once; a few, such as 'Autumn Damask' and some Portlands, Hybrid Perpetuals, Bourbons, Chinas and Noisette roses tend to flower again. The majority of modern roses flower over a long period.
There are three main techniques for pruning roses:
Prune in early spring when about half the buds are swollen, but before the leaves start to expand. Take off ⅓ to ⅔ the length of the canes, cutting back to an outside bud. Reduce the plant to a total of 3 to 6 canes. These roses respond well to hard pruning. The lower the pruning cut the stronger the new growth will be. A hard pruning encourages the growth of strong canes from the base of the plant that will produce the best flowers. When finished pruning these roses, the framework is anywhere from 6 inches to just over one foot tall.
These roses will bloom on new growth as well as laterals of one- and two-year old canes. Cut back main canes by half and laterals to just two buds. Thin out branches that are older than three years.
Do not prune a climbing rose for the first three years; only remove dead, damaged or diseased wood. After three years, cut back laterals in the early spring to two or three buds or about six inches. On a mature climber, selectively thin out older canes by cutting down to the base.
Prune in mid-summer after flowering (usually mid- to late-June). Prune these shrubs lightly to shape them. They generally do not need a severe pruning, but benefit from being thinned out.
Some people like to prune their roses in the fall. If you are covering your roses up for the winter and protecting them with burlap or a wire cage stuffed with leaves, pruning will be necessary to reduce the size of the rose. Here, in the NYBG Peggy Rockefeller Rose Garden, we pull mulch up around the base of the rose to form a 6 to 8 inch mound. This creates a protective winter coat that is removed in early spring. They are not pruned at this time of year since there is no way of anticipating which branches will die or be damaged during the winter and which ones will survive. The selection process is therefore made in the spring. An exception would be if a rose were too large and there was concern about the stability of the rose and the possibility of wind damage. Then, the rose would be pruned back to a more compact shape.