How To Prune or Renovate Knockout and Other Shrub Roses
“My knockout is out of control!” a reader told me. “How do I prune it?” Knockouts are one of the many varieties of shrub or landscape roses, and many people are surprised by how large they typically grow. I’d urge you all not to think of these are “out of control,” however. They are not running around starting fires, stealing cars, or abducting children. That would be out of control. No, these shrubs are merely growing to be the size and shape their genetics dictate. Yes, they may need a good pruning or even a complete renovation, but this is usually because the gardener has ignored them for a few years, and now they are a thorny ball of living and dead stems.
Here are the steps for renovating a shrub rose. There are two ways to do this: a drastic renovation, and a partial-renovation that is a very thorough pruning. The goal for each is to improve appearance and stimulate new growth. Let’s look at the partial renovation first, since this will be most suitable for those who still want flowers after pruning.
UPDATE PHOTOS BELOW 5/21/20222
This is how my shrub rose looked today. I’ve done minimal pruning on this plant for the past five years. It’s time to get in there and clean it up! But I’m not ready to do a drastic, cut-to-the-ground pruning. (More about that later.) So I start by looking at this plant and finding the biggest, oldest stems.
These are the tools you’ll need for a good pruning of a shrub rose. On the top, hedge trimmers. In the center, a pair of good by-pass hand pruners. (Spend the big bucks for these if you can. When it comes to pruners, you get what you pay for and a good pair make pruning SO much easier and faster.) Below, by-pass lopers. Lopers are like a hand pruner but larger, so they can cut thicker branches, and with longer handles. The long handles of lopers are especially valuable for roses since you’ll want to be able to get into that thorny bush to cut, without getting pricked yourself.
Look at the base of the rose bush and locate the largest, oldest stems. The age of the rose and how long it has been since it has been pruned will determine how many large, old stems there are. On this plant we can see at least 3 very old stems and 2 that are close. This year I will cut the 3 oldest, leaving the others for next year or the year after.
Use the lopers to cut the oldest canes (aka stems) back toward the base of the plant. You can leave about 6 to 8 inches of the stem, since new growth might be produced from below that cut.
This is another large, old cane that will get cut way down. This removal of oldest stems is important because it stimulates growth of newer, more vital canes. Once you cut these large, older stems, use the lopers to grab them without cutting, and pull them free of the shrub.
Now look at the plant and find any curved, weak or funky shaped branches. Look for those growing into the center of the plant instead of flowing out, away from the middle. Remove those that you see. The arrow points to a funky shaped branch that goes into the center, so I am cutting that out near the ground.
The next step is to remove dead stems. If you wish, this can be started by using a hedge trimmer to cut the dead tips and last year’s seed pods. You can go chop-chop-chop with the hedge trimmers, to remove these off the top. You’ll still need to go back with the hand trimmers to remove all the other dead stems throughout the rose bush. But this can be a fast start in this process.
Now look very carefully and identify all dead or “mostly dead” stems. Remove them completely. Take your time – this process isn’t one that should be rushed. Rela
Here you see the pile of dead stems at the base. The more you look at your plant, the more deadwood you’ll find.
After all the dead stems are gone, look for any remaining canes that go into the center of the shrub, or are odd or funky looking. Remove those, and then clip a bit off the top – about 6 to 12 inches. Make the cut just above a bud that faces out, away from the center if you can. Know that every green shoot you leave will become a stem with flowers at the end. Roses produce blooms on new growth. So leaving all of these branches with green growth will result in a plant that has a good amount of flowers this year. I have removed about 1/3 of this plant’s total stems.
The more drastic renewal pruning is when you cut the rose down closer to the ground. This isn’t the preferred way to prune Knockout roses and other shrub varieties, but it might be necessary. Rose bushes don’t always recover from such a major renewal pruning, and they won’t flower much the first year after you cut the down, Occasionally this type of pruning will trigger growth from below the graft – watch for fast, straight-up shoots that come from the ground, not the stems above the ground. Growth that comes from below the graft will have different flower shapes and colors.
The other, much more drastic way to renovate shrub roses is to cut all of the stems down to about 6 inches tall. In most cases the plants will come back, but in some instances you will not get strong, return growth. So only do this is you are desperate and willing to let the plant go. If the rose bush does recover, you will need to wait at least two years before it looks good again. And you’ll need to be prepared to clip it and tweak the new growth so that it develops a full, balanced shape. If you go with this method, sprinkle an organic fertilizer around the area and then top-dress around the cut stems with compost or composted manure after you prune. Through the rest of the summer, water these plants deeply once a week if nature doesn’t deliver at least an inch of rainfall. Mulch over the compost to hold moisture in the soil and discourage weeds.
I had three shrub roses in this area. One was pruned as first described in this blog, by removing about a third of the plant’s total growth. The other two were given the drastic, down to 6″ renovation pruning. I’ll post followup photos later in the summer to show how all of these plants are doing.
The older your shrub rose, the more time it will take to prune it. Needless to say, the drastic renovation that you see on the two plants on the right is faster, but not the first choice for most plants. Know that even with the thoughtful cutting that I did on the plant on the left, there is more that could be done! There is a stem that grows from the right side into the center and to the left, for example. I will cut that out next year.
Shrub roses are wonderful in that they are disease resistant and repeat flowering.
If your shrub rose is newer, and doesn’t need renovating, prune it by first taking out all dead stems and the tips of the canes that have died back over the winter. Next look for stems that are heading into the center of the plant instead of moving out and away – remove those by cutting them near where they join another branch. Last, clip branches back from the top down, cutting just above an outward facing bud.
Here is one of the shrub roses that I did a renovation pruning on, cutting it down to about 6″ from the ground. It’s filled with new growth! I’ll post photos later in the summer to show you how this plant has been rejuvenated .
Update on May 2st: This is the base of the plant that I didn’t cut all the way down, but removed some of the largest, oldest canes. See all of the new growth below? The shrub still has new growth on the top, which will produce flowers soon, but there are also new stems forming here on the bottom, that will fill out this summer.