The technique of pruning varies with the type of rose and the landscape purpose for which it was planted, whether it’s growing in the ground or in a container. Pruning can range from removing unwanted buds to severely excising canes. Proper pruning stimulates growth at the buds closest to the cut, which produces new flowering stems.
The first step in pruning any type of rose is to remove any dead, damaged, diseased, or weak and thin canes, cutting them off flush with the bud union or, in the case of own-root plants, flush with the crown. Look for any canes that are broken or wounded, or that have cankers (dark, sunken lesions caused by a fungus), and prune below the injury, at the highest point where the pith (the central portion of the cane) is healthy and white. Make the cut exactly 1/4 inch above a growth bud. If the injury extends below that point, cut to a lower growth bud.
Next, remove canes that are growing into the center of the plant or those that cross each other. Canes that grow inward keep light and air from the center of the plant and will eventually cross, chafing one another. These abrasions can become entry points for insects and diseases. Using shears cut these canes down to their origin, whether that is another cane, the bud union, or the crown. It is important to keep the center of the plant open to let in sunshine and allow air to circulate freely.
Always prune to an outward-facing bud so that canes do not grow into the center of the plant. Prune at a distance close enough to the bud that no stub remains to die off and harbor insects or diseases but far enough away that the bud will not die. A good distance is about 1/4 inch above the growth bud. Equally important, cut at the proper angle so that water runoff won’t drip on the bud or collect in the cut and retard healing. The ideal angle is 45 degrees, slanted parallel to the direction of bud growth.
Pruning in Warm and Cold Climates
In warm climates where rose plants grow quite large, pruning to the recommended height is not desirable because it will remove too much of the plant. Instead, prune away about one half to two thirds of the plant each winter or early spring by removing the older canes and shortening the remaining canes. In cold climates where there is a great deal of winter damage, pruning heights may be determined for you by the amount of winterkill. Prune canes down to where there is no more winter damage, even if it is almost to the ground.
The higher a plant is pruned, the earlier it will flower. But don’t jeopardize the health and vigor of the plant by pruning too high just to have blooms a few clays earlier. There is little advantage to pruning your roses lower than the heights prescribed above; unlike disbudding (which we’ll discuss later); it will probably not make the plants produce larger flowers.
Preventing Disease
Although black spot and other fungal diseases manifest themselves on leaves, their spores can over-winter on rose canes. If these diseases plagued your roses during the previous summer, you should prune them lower than recommended, cutting away and discarding much of the source of the problem. Although you won’t be able to see the spores on the canes, you can be assured that cutting off a few extra inches during spring pruning will reduce the number of spores to some degree. Never leave rose cuttings on the ground. They look unsightly and harbor diseases and pests that may potentially re-infect the plant or spread to others.
When to Seal Cuts
Pruning cuts more than inch in diameter can be sealed with pruning compound, orange shellac, or grafting wax (available at garden centers or hardware stores) if boring insects are a problem in your area. Pruning compound and orange shellac are the easiest to use because they can be painted on. Otherwise, sealing is not necessary. Some types of white glue, which is sometimes used as a sealant, are water soluble and will wash away with the first rain or watering; they should therefore not be used.
Inspect After Pruning
Several weeks after you have pruned, take a second trip through the garden with your paining shears. If you pruned early in the year, a late frost may have caused minor dieback on some of the canes. This dieback should be removed. Cankers that were not apparent at pruning time may be visible and should also be pruned away.
Don’t be too harsh when pruning young plants. Until plants are well established and have been growing robustly for two to three years, remove only weak, damaged, or dead wood. Shape and shorten the plants as recommended above without cutting away any of the older canes. In the following years, old canes can be removed as new ones develop.
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