Q. When is the best time to prune a rose bush (month)?
The ideal month depends upon the type of rose and the weather pattern in a given year. 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.
More specific guidelines by rose type are as follow:
Hybrid Teas, Floribundas and Grandifloras: 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.
Repeat Blooming Modern Shrubs and Repeat Blooming Old Garden Roses: 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.
Repeat Blooming Climbing Roses: 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.
Once Blooming Modern Shrub and Old Garden Roses: 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.
Courtesy of NYBG Plant Information