Now is the time to cut back knock-out roses. They should be pruned no shorter than 18″. Knock-out roses are a grafted rose, meaning if you cut the rose back too far you’ll cut off the hybrid “knock-out” rose and end up with a wild native rose. If you wait much longer to prune your knock-outs you will be removing new growth and current blooms. Some people choose not to cut back knock-out roses, but you should know that they have the potential to get fairly large and scraggly. When cut back they keep a nice tight tidy appearance and will have an abundant amount of blooms. After pruning, early March is a good time to fertilize your roses for the upcoming season.