The perfect time to cut back shrub roses, including the popular “Knock-Out” series, is when they are just starting to sprout new growth. The new shoots in spring will tell you where the plant is strongest. It’s important to be patient; if you cut roses too soon, or in the fall, they will die back from your cuts and need corrective pruning later. If you prune too early, late frosts could shock tender new shoots.
The early spring “haircut” we’re about to describe, plus a good feeding, are just about all the care Knock-out roses need to perform their best all year. Put on a pair of stout leather gloves for this job. Start by raking the dead leaves from around the plant so you can see all the branches.
Now, look for stubs from last year that have died back and rotted, and cut them off at the base. On older plants there are probably lots of thick dead canes; these should be cut off at the ground. We use a Felco 600 pocket-sized folding pruning saw for this job.
Now take a good sharp bypass pruner (Felco 2 is our favorite) to cut off any branches that are lying along the ground. Clip off the tangled “baby branches” and zigzag clutter around the base of the plant. Any stems smaller than a pencil should be removed. Now you can clean out all the dead leaves and weeds from underneath. This rotten stuff harbors disease and insects and will make your work harder if you don’t remove it.
Now, cut the main canes down to about half. Look for the healthiest, fattest shoots, particularly the ones pointing outward, and cut off everything taller even if it’s alive and well. You want to leave only the straightest, healthiest canes, and they should be no more than a foot to 18 inches tall. Make your cuts just above good, healthy, outward-facing shoots, cutting on an angle just above the shoot. This directs the growth outward and doesn’t leave a stub that will rot. The outward-facing shoots will become the new main branches, opening up and expanding the plant.
Make sure you make your cuts below anything dead or rotten. The cut end should be green and healthy-looking, without a brown center. A good rule is to cut more and further rather than less. You can’t harm the plant by cutting too much; the remaining canes can be as short as six inches and that’s fine. We call this “tough love”. You’ll be amazed how quickly the plant replaces all the little “busy branches” you are removing with healthy new canes.
Now you should fertilize with a good rose fertilizer. We like Espoma “Rose Tone” the best. A pound or two is enough for one feeding. Just scatter it around under the plant. Next you should spread a little mulch to keep weeds from getting a head start before the rose gets bushy and shades the ground. We prefer pine bark nuggets for roses because they allow the plant roots to breathe. Pine nuggets also dry out quickly, good since moisture encourages fungus problems with roses.
A good haircut right now will make your shrub roses bloom their best. Your neighbor’s Knockouts might bloom a few weeks sooner than yours, but yours will be healthier in the long run. Shrub roses bloom on new growth and a good pruning and feeding encourages new growth. Now you can enjoy a spectacular show for the rest of the year!
Steve Boehme is a landscape designer/installer specializing in landscape “makeovers”. “Let’s Grow” is published weekly; column archives are on the “Garden Advice” page at www.goodseedfarm.com. For more information is available at www.goodseedfarm.com or call GoodSeed Farm Landscapes at (937) 587-7021.