Hydrangea macrophylla 39bloomstruck39 flowers from may until september and throughout these months this shrub is full of beautiful flowerheads each measuring up to 13cm in size that grow on bright red shoots what is fascinating about this hydrangea is that the colours of the flowers depends on the ph of your soil if the soil is acidic the petals will be violet blue and if the soil is alkaline then the petals will be mauve pink in autumn the foliage turns to shades of red and gold wh