Knockouts are tough and you can't really go wrong no matter what you do. I typically cut them back maybe halfway in late fall (to keep the wind from blowing them all over the place) and then in mid-March give them a final trim back to about 12 inches or so.

Larry

Thanks for the information. I will trim them in March.

I would only trim them to control size. They do not need to be pruned like a hybrid tea as you might be thinking of . They will bloom their heads off regardless of how you trim them. If needed, I would trim them in late winter as suggested, just before the new growth starts.

If you planted them last year, maybe just trim deadwood this spring. If they've been in the ground for a couple of years you can get more aggressive. Most of my Knockout's are 5? years old and I'm going to prune really hard this year as they're out of control for the spots they're in.

I trim mine to make them a little bit more open in the center. May be this year, I'll trim to reduce size. I just met a lady who has 150 roses (mostly fragrant antiques) in may be 1/4 to 1/2 an acre or less, and all she does is spray with sulfur weekly and shovels on leaf mold and for a few a little fertilizer. You should see those bushes. I am aiming for something similar in part of my garden. I was totally amazed.

So I understand it would be OK to trim back now in Nov. even though temperatures are down in the 40's at night.

becker, if the shrubs are too big for the spot they're in, you can cut them down now.

If they're not too big, then there is no need to "trim" at all.

Mine are 6' x 6' after four or five growing seasons and they have to be taken down a peg (or maybe even removed).