According to the Royal Horticultural Society (RHS), if you have acidic soil (with a pH of 5.5 or lower) then this should produce rich blue flowers due ... also acting as a natural fertiliser ...

Q: Why are more fruits and flowers red, orange or yellow than blue? —Robert L. Morrison | Poughkeepsie, New York There is actually no true blue pigment in nature. A pigment creates color by ...