Now is the time to prune Knockout Roses. Cutting them back at this time of year will rejuvinate the plant and you will have thicker roses. Use a sharp pair of hand pruners or loppers and make your cuts just above where the lower branches start to divide off of the main stalks. Try to make your cuts at about a 45 degree angle so that water will roll off the cuts. You can also remove any dead branches completely. Fertilize with a granular rose food and water it in. In a few weeks you will see lots of new growth and before you know it your Knockouts will be full and lush.