Red Knock-Out Roses & Blue Salvia together in a border. -Stepheny H adds: How about this for curb appeal, yet a great example of a garden border that works. I grow Knock Outs. Just be careful where you plant them. They get big! Trouble free, however, and a lovely addition to any garden. Where to pin this? Thou shall not covet? Plant combinations that work? This is a winner.