My rose bush is already full of green leaves. Can I still cut it back?
Pruning Knockout Rose Bush
You might want to wait until it blooms or you will likely sacrifice many blooms in the first bloom cycle. If just a light pruning back is all you want to do, then you would likely be okay. However if it is a big shaping pruning, I would wait until the first flush of blooms is just starting to die back. Then prune them back, feed them and water well.