I've planted up a south facing border in my garden and I think I may have made a mistake when I put these plants near each other. The plant on the left is a rock rose, middle plant is Californian lilac and the plant on the right is a Hebe. All have grown loads since I bought them. I'm worried that the lilac will take over. Can I safely move the Hebe further to the right to give the lilac more space?