The gardening subject with the most advice and the greatest anxiety is pruning roses. January is the right time of the year for this task (with some inevitable exceptions, which we’ll get to), so let’s review.
Gardeners have good reasons for being uncertainty about pruning roses.
The need for pruning arises from the gardener’s priorities, not the plant’s requirements. This is evident from the existence of wild roses and so-called “cemetery roses” that thrive for generations without the care of any gardener. Pruning and other forms of rose cultivation are intended to produce more blossoms, larger blossoms, more desirable plant forms, and healthier plants.
If all roses were the same, pruning would be a simple matter, but the genus Rosa includes over 360 species, some of which are in cultivation since at least 500 B.C. This botanical diversity complicates the task: several of these species respond better to some pruning practices than to others.
Several species have been hybridized extensively, and thousands of cultivars have been available. The cultivar, however, does not determine the preferred pruning practice; more important determinants include the species and the form.
Roses are generally described in three major classifications: wild (or species) roses, old garden roses, and modern garden roses.
Old garden roses typically bloom once on old growth each season and are cold hardy. They require only minimal pruning, which is done after blooming primarily to manage the overall size and shape of the plants.
For this column, we’ll focus on modern roses, which by most accounts began in 1967.
Modern garden roses are typically hybrids derived from the very old China roses. They are most popular in today’s gardens and characterized as blooming on new growth, and ever-blooming, i.e., they continue blooming throughout the growing season. They are not cold hardy and a hard freeze can kill branches or entire plants. In the Monterey Bay area, cold weather is not a significant threat to these plants.
Pruning these plants begins with removing dead wood, and any branches that are diseased, broken or crossing other branches. These “clean up” actions prepare for cultivation pruning.
Modern garden roses generally benefit from a hard pruning to stimulate the new growth that will produce blooms. This is done during dormancy before new growth begins. In the Monterey Bay area, the best time to prune these plants is in during January and February, so right now is a good time to begin your rose year.
“Hard pruning” has various definitions, with most ranging between one-third to one-half of the canes. One approach calls for removing one-third of the canes entirely, then cutting the remaining canes by one-half.
One intriguing approach to pruning modern garden roses is to simply cut the plant down to eighteen inches in height. Shearing a rose in this way has been claimed to yield the most foliage and blossoms.
The so-called classical approach to rose pruning involves cutting canes to one-third or one-half, cutting at 45-degree angle to an outward-facing bud, opening the center of the plant for optimal light exposure, and removing branches that are thinner than a pencil. This approach yields larger stems, longer stems, and larger blossoms.
Whether you use the classical or shearing approach to hard-pruning your modern garden roses, the important message is to prune them at this time of the year. They will respond beautifully in the spring.