Take cues from weather when deciding to prune roses
In warm climates, roses do not go completely dormant, and the sugar produced by the plant stays mainly in the branches. Between going totally dormant and totally evergreen determines when and how to prune.
Here in the Antelope Valley, roses go about 80% to 90% dormant, meaning most of the sugar is stored in the roots and some is still stored in the branches. A good way to determine how dormant the rose is to check for the number of leaves still on it. If all have naturally fallen off, the plant is very dormant. The more leaves on the rose, the less dormant the rose.
Knowing how dormant your rose is determines how much you will prune it. If you prune off too much in warm areas like Los Angeles, you remove too much sugar stored in the plant’s branches. The plant will not grow back as well the following year, trying to make up for the lost sugar. In locations where plants go into a heavy dormancy, if you do not prune the plant enough, the plant will produce a lot of small spindly growth and small flowers.
When I prune hybrid tea, grandiflora and floribunda-type roses, my first step is to cut the entire plant off to about 3 feet tall, except for tree roses, climbing and miniature roses. This allows me to see the entire plant easily.
The second step is to remove the dead, damaged and diseased branches (branches in roses are called canes). The next step is to remove suckers. Any canes growing below the bud union are called suckers. The bud union is the location (usually at the base of the plant) where you will notice a large swelling of the trunk.
I need to remove any canes that start growing on one side of the plant and grow through the middle. These are called crossing branches. Next, I want to select three to seven canes to leave on the rose bush. I am looking for canes that are spaced symmetrically around the bush when I look straight down on the bush.
I like about half of the canes to be new wood keeping my rose bush rejuvenated. The newer canes should be thick, healthy green branches. The older canes will have brown stems. All other canes should be removed now. The rose bush should look like a vase after this step, meaning there should be an open center with branches all around the edge.
The last step is to re-cut all the remaining canes back between 18 and 24 inches high, just above a plant growth bud. A growth bud is just above a leaf or where one was before it fell off. The bud should be facing out away from the center of the rose bush.
If the winter has been cold and all the leaves have fallen off, I try to cut back closer to 18 inches. If the winter has been warmer and there are still leaves left, I cut back closer to 24 inches or even 30 inches. So far this year, I will be pruning closer to 24 inches. In the landscape, you may have some roses in protected areas that require less pruning than roses in cold areas. The key is to see how many leaves are still on your roses.
Tree roses and climbers are not pruned the same way as I explained above. A climber rose would be cut back to about 5-foot-long canes. A tree rose is pruned the same as above, but the bud union is about 3 feet above the ground. This means the last cut should be 18 inches above the bud union, not the ground.
The key to a successful rose pruning is to cause the rose bush to grow back next spring as large or slightly larger than before it was pruned. If the rose does not grow as big next spring, then make the last cut higher next winter. As with any pruning, keep your tools sharp and clean. And with the wet winter be sure to disinfect your shears with one part bleach and 9 parts water between each rose that you prune to help prevent spreading of some diseases.
If you had problems with mildew, rust or black spot on your roses last year, be sure to remove any remaining leaves, flowers or hips from the plant and the ground. Spray your plant with a fungicide labeled for roses and mildew. Also, spray the ground around your plants especially if you have decorative bark covering the soil.
I believe the optimum time to prune roses is the last week of January, but you can prune now. If you have a lot of roses or limited time, you may want to start pruning now.
There are probably more books written on roses than any other gardening topics. Roses can grow anywhere in the United States, but the best way to prune roses depends on how cold the winters become.