Sharpen your shears and don your armor because it’s time to prune roses.
In the San Francisco area, most roses are pruned between mid-December and the end of February, when the plants are dormant. The exception is old-fashioned roses that bloom only once a year. They are pruned lightly right after they finish blooming in the summer.
Your shears, lopper and pruning saw should be sharp and well-oiled. You should be dressed in clothing that will protect your skin from the sharp prick of thorns. Gauntlet-style gloves that cover your forearms are great for the task.
Your goal is to end up with a bush that has four to seven young and healthy canes extending upward from the base of the plant in a vase-like shape (You also can think of it as the shape of a cupped hand). The new canes you leave on the plant should be larger around than a pencil. New canes are a bright and smooth green or mahogany. Old canes are wrinkled and gray.
Start at the base of the bush and remove the old canes, cutting closely to where the canes emerge. Remove new canes that are smaller around than a pencil. Do not leave stubs.
You also want to remove any dead, diseased, damaged or weak growth. This includes suckers, which sprout from below the base, or bud union, of the plant. The bud union looks like a gnarled knob. Canes spring from the bud union.
When you have only the handful of new canes that you want to keep, cut off any stems from those canes that cross into the center of the bush, or cross each other. Remember, when looking down into the plant, you want it to be cupped and open.
Now you’re ready to prune the rose to the height you want. A general guide is to prune the remaining canes to between 18 inches and 36 inches, depending on the type and size of the rose. Generally, you don’t want to remove more than one third of the healthy growth. Here’s where it gets a little tricky, so take your time: You want to prune just above an outward-facing bud. Buds aren’t always easy to see. Sometimes they look like a small reddish dot. Sometimes they look like a smile. You want to cut above an outward-facing bud at approximately a 45-degree angle, so that the upper point of the cut is about one-quarter inch above the bud. In other words, your cut is slightly higher and at an angle from the outward-facing bud. You’re pruning in the direction that you want new growth to go: angled up and facing out.
Now comes cleanup. Remove any leaves left on the bush and all leaves that have fallen to the ground. They are likely to be infected with a fungus such as blackspot, rust, or powdery mildew — all common diseases for roses. Don’t compost the leaves, pitch them.
Finally, spray the bush — really drench it — and the soil beneath it out to the drip line with a horticultural oil or dormant spray made to smother insect eggs and fungal spores that might be left on the rose.
Want hands-on practice in pruning rose bushes? Come to the San Mateo/San Francisco Master Gardeners annual rose-pruning clinics Jan. 14 and 28 in Burlingame. The Jan. 14 clinic is from 9 a.m. to noon at Washington Park on Burlingame Avenue. The Jan. 28 clinic is from 9 a.m. to noon at the Rose Garden on Park Road, located south of Burlingame Avenue.
San Mateo/San Francisco Master Gardeners rose-pruning clinics
Joan Tharp is a University of California Cooperative Extension master gardener. She lives in San Mateo. She can be reached at email@example.com.