Who doesn’t love the Knockout®, a beautiful tough-as-nails repeat-blooming shrub rose available in more than half a dozen types and colors. Conventional wisdom says that gardeners don’t really need to prune Knockouts, and that’s true – sort of.
If you’ve had some successful Knockout roses, you know that they’re vigorous growers. A Knockout can easily get to be the size of a Volkswagen Beetle in a few years. If your Knockout is starting to take over the flower bed and develop an attitude, it’s time for a good pruning.
Forget the folderol about pruning an outward-facing stem, cutting above a five-leaf frond, and all that prissy business. Be brave! Don those rugged garden gloves, grab your freshly cleaned and sharpened pruners, and get to work. Knockouts can take a good deal of pruning and come back ever better than they were before. First, cut out any dead branches. Next, simply cut the thing back to a manageable size – whatever it is. You can remove up to 2/3 of branch length all over and that Knockout will just laugh and start growing some more.
I cut my Knockouts back twice a year – once in the early spring while the bush is still mostly dormant and the worst of the winter is over, and again in late summer. Why late summer? Because once the searing heat is over, that rose is going to want to put on a great show, and to do its best you need to give it an all-over haircut. That early spring cut is a serious pruning, and the late summer ‘do is a good trim all the way around. You will cut off some buds in this late summer trim, but don’t despair; there’ll be three more coming out for every one you cut off.
Last summer, we had crazy hail storms and my Knockout topiary got pretty wrecked. I let it go that year, and it gave me a few lopsided blooms. This spring, I cut that thing back to almost a nub, figuring I had nothing to lose if it didn’t make it. It looked like an organic Sputnik model, a lumpy knob on a big stalk with a bunch of little twigs sticking out all over. Did that Knockout care? Not a whit. Within three weeks it looked like a giant green and red basketball, covered with new lush foliage and tons of flowers.
While the Knockout is resilient, it’s not fool-proof. So don’t be a fool and cut it back in the middle of winter, or you’ll experience the heartbreak of winter kill. And if it’s just a leggy mess all year then it’s probably not getting enough sun; cut it back and move it somewhere else in the yard that gets more sun. They don’t mind being moved, as long as you have a good reason for doing it. If you don’t have any sun in your yard, dig the thing up, re-pot it, and re-gift it to a friend with a sunny yard.
So be brave and shape up those Knockouts. They’ll repay you beautifully.
Pictured: Three weeks after I pruned my Knockout topiary down to a nub, it bounced back with tons of new growth and blooms.