Faithful reader Mandi Villa writes, “I love my ‘Knock Out’ rose, but it’s getting too big. Can I prune it without killing it?”
Yes, Mandi, you can. In fact, you can do almost anything to a ‘Knock Out’ rose without killing it short of rocketing it into the sun. But if you want it to follow the pruning with scores of blooms on a tidy plant, you must follow Grumpy’s rules on when, why, and how to do it.
When To Prune
‘Knock Out’ (red, pink, double, etc.) blooms on new growth. This means that you can prune it almost anytime you want without ruining the season’s bloom. If you prune now, you’ll remove some flower buds and delay flowering, but you’ll get lots of blooms in a couple of weeks. During the growing season, ‘Knock Out’ typically explodes in bloom for a few weeks, goes into a resting phase, and then explodes in bloom again. A resting phase is a good time to prune. About the only time not to prune is late summer and early fall, as this might encourage late growth that wouldn’t harden off in time for winter. In the North, winter is not a good time to prune, but winter is just fine in the South.
Why To Prune
Although ‘Knock Out’ is marketed as a compact shrub, over time it gets pretty big. A neighbor of mine has a ‘Knock Out’ hedge that’s six feet tall. So periodic pruning is necessary to keep it manageable. ‘Knock Out’ also tends to produce a lot of fruit, called “rose hips,” that inhibit future flowering. Trimming these off brings it back into bloom.
How To Prune
First, put on some heavy leather gloves. Grumpy only knows of one thing possessing more vicious weapons than the thorns of ‘Knock Out’ rose.
And that would be Wolverine.
Now that you have gloves on, let’s proceed. Use a good pair of hand pruners to shorten small branches a half-inch thick or less and loppers for thicker ones. Cut back to a leaf or an outward-facing bud. Remove dead, crowded, or crossing branches to open up the plant’s center. Cut back aggressively if you want, but not down to the graft union. That’s the knob at the base where the roots and stems meet.
What’s In A Name?
A while back, Grumpy received a nasty letter from lawyers representing the outfit-that-shall-remain-nameless that patented this plant. This notice informed me that I had willfully misspelled the name ‘Knockout’ instead of the correct way, ‘Knock Out,’ and demanded immediate remediation. You can see why spelling it the former way could cause an asteroid to slightly alter its orbit, smack into the Earth, and extinguish all life.
Here’s the ironic part. The official registered name for this cultivar of rose isn’t ‘Knock Out.’ That’s the marketing name. The cultivar’s true name is ‘Radrazz.’ Therefore, I suggest all of you ask only for ‘Radrazz’ rose when you visit your garden center.
Wouldn’t that be fun? I imagine the exchange would go something like this.
You: “Do you have any ‘Radrazz’ roses?”
You: “‘Radrazz’ roses. They bloom all summer.”
Salesperson: “I got some red, red roses. Got some pink, pink roses and white, white roses too.”
You: “No, ‘Radrazz’ roses.”
Salesperson: “Red raspberry roses?”
You: “No, I mean the roses that everyone in America is required by law to plant by the dozens in their yards every year.”
Salesperson: “Oh! I bet you mean ‘Knockout’ roses.”
You: “How dare you spell that wrong! I heard you! You pronounced it as one word. It’s two. ‘Knock Out.’ My lawyers will be sending you a letter!”
Salesperson: “If you don’t haul your fat behind off of my property right now, “knockout” will refer to your state of consciousness.”