Is it too late to trim back my 'KnockOut' rose bushes? Usually do it in early spring...but missed doing it.
It depends on how late you are on trimming them. Cutting back your KnockOut rose bushes during summer they will be stressed by the intense heat. As a result, flowers can be tiny and not as pretty as you will expect. You can read more at http://www.nola.com/homegarden/index.ssf/2012/08/knock_out_roses_add_no-fuss_be.html.
No it isn't too late. You can do it now however, cut back in the early morning hours or late in the afternoon early evening when the sun has set. After pruning, make sure to water the soil well afterward to prevent shock...
You probably will lose some flowers, but you won't hurt the plants. Be sure and water them well