Q&As/Flowering Shrubs and Trees/Blue Hydrangeas
How do I turn my hydrangeas blue? Is there anything I can add to the soil?
Blue flowering hydrangeas naturally retain their colour when growing in soils with a pH of 4.5 – 5.5 i.e. acid soils.
Where soils are not so acidic, i.e. with a higher pH, the blue flower colour can be achieved with applications of aluminium sulphate every few weeks, especially early in the growing season. Dramatic changes in the colour of hydrangea flowers do not happen overnight and in some instances may occur only slowly over the growing season.
Apart from the variable flower colour, hydrangeas require little attention except winter pruning when the old growth is completely removed. While not blue, a lovely variety to grow is Hydrangea Paniculata, a vigorous growing shrub that produces masses of large, triangular-shaped heads of white blooms for many months over summer.