The answer is clearly no. The reason that I suggest to prune your roses now is to remove the first heavy flush of growth after your Knock Out roses have passed their first full display of color. Established Knock Out roses can grow more that 24" in April and May. If you decide not to prune them, they will continue to grow and bloom all summer, but the roses will get large. If you have your Knock Out roses as a landscape plant and you have plenty of room for them to grow, you may not need to prune your roses as heavy as I am suggesting.

If I prune my roses now, when do I prune them again?

The next time that you will prune your roses will be in late November when most of the foliage has fallen to the ground.

This is what my established Knock Out roses looked like BEFORE I pruned them.

You can see the purple ribbon that I have tied to a stake so you can determine just how much I have pruned.

Remove at least 12" of new growth with pruners or shears.

You can see how much I trimmed from my Knock Out Roses

Knock Out Roses AFTER pruning

Fertilize your Knock Out Roses with Evergreen Roses Food