How Do I Get My Hydrangea To Change Colours?

            Hydrangeas can produce an amazing range of colours.  Not only that, but the same plant can change the colour of its blooms within a single growing season.

            The intensity of colour depends on the genetics of the plant (variety) and how much sun they get (blooms in more sun are paler).  Also, white flowering hydrangeas will never go truly pink or blue... but they may get tinges of pink and red in their petals as they age.

            The funniest varieties to play with will bloom purple-blue or pink-red, depending on what you do to their soil.  Flower colour responds to Aluminium levels, as well as soil pH.
            There are commercial products in most garden centres that you can add to the soil to get hydrangeas to change flower colour.

            It's easier to change from pink to blue than back again.  Once a month in the growing season, add either vinegar (well-diluted) or a dose of aluminium sulphate to the soil to make flowers change from pink to blue.  

            From blue to purple:  add lime to the soil, this raises the pH (makes it more alkaline).  To try to get to pink flowers, once a month in the growing season add about 4 ounces of lime around  the roots of the plant, until you get to the desired shade of pink.

When do you prune hydrangeas?