I have a lithodora "grace ward" and rock foil (saxifraga x.a. "purple robe") that I am trying out in my garden. The flowers should be blue and red, respectively. Before I planted both in the ground, the lithodora had all blue flowers. The rock foil had not flowered yet. However, after I planted both in the ground, the flowers started coming up white.
I know the color of hydrangeas will vary with the pH, but haven't heard the same of these two varieties. Any ideas?