Roses usually need a certain amount of pruning every year. The best time to do the pruning is early spring after danger of killing frost is over. This falls in late march or early April in the Washington area, earlier as you go south and later as you go north.
Some specialists recommend that rose plants which suffered from black spot, a fungus disease, last year should be cut back to 6 to 12 inches. The fungus over-winters on the canes may be reduce the chances of new infections, they say. The prunings, of course, should be removed from the garden area.
Other specialists claim that such heavy pruning helps very little in disease prevention. Repeated application of a good fungicide, such as Benlate or Phaltan, will take care of it, they say.
Some gardeners cut roses back to about 12 inches anyway in the hope of getting larger blooms on longer stems.
One thing is certain. Rose bushes left at 3 feet or more in height will bloom earlier in the season and bear more flowers. The canes and stems that remain after such light pruning will provide lots of new twigs and leaves, and the leaves will produce the food necessary for good health and vigor and lots of flowers.
Dr. A. G. Smith, Jr., Virginia Tech horticulturist, once estimated it took 15 to 20 healthy leaves to provide the food necessary for the production of one rose on a hybrid tea.
The more healthy leaves the plant possesses, the more flowers it will produce.
The main purpose of pruning roses is to remove all the dead and diseased wood. Also, the least desirable of two branches that rub against each other should be removed.They scratch each other with their thorns, permitting infection by disease organisms. All small twigs on the upper part of the plant should be removed.
Any additional pruning is likely to reduce the number of flowers produced in the early part of the season.
Use sharp tools to do the pruning. Dull shears are likely to crush the stem and the wound heals slowly, if at all.
When a cane or branch is shortened, the cut should be made 1/8 of an inch beyond a bud. If it is at a greater distance, a stub is left and the stub will die back.
The bud to which the cane is cut back will normally make the most growth in length. An upright bush can be made more spreading by cutting back to outside buds, and a spreading bush becomes more upright if cut back to an inside bud.
Grandifloras and floribundas are pruned about the same as hybrid teas. Thin out the tops of the roses and shorten the stems that are left. This keeps the plant from becoming top heavy.
Minature roses should have long shoots shortened. Thin out the top and cut it back somewhat to encourage new growth.
New modern climbing roses are sports or mutations of hybrid teas. Sometimes they do not bloom much for a couple of years after being planted. During this period very little pruning should be done.
Afterwards the side branches on long canes can be cut back to about three buds each. Most of the length growth of cnaes should be left unless they are getting too long for the place where they are growing.
A group of climbing roses such as Paul's Scarlet blooms only once a year. Prune these after the flowers fade. Remove old canes to encourage new ones to grow as replacement.