Despite common misconceptions, not all shrub hydrangeas will change colour. Only certain varieties of Hydrangea macrophylla or Hydrangea serrata have this unique feature!

While white varieties will always bloom white, any coloured varieties of Hydrangea macrophylla or Hydrangea serrata will change colour based on the pH of the soil. An acidic soil will produce blue blooms while an alkaline soil will produce pink blooms. Here in Ontario, the soil is naturally alkaline so the shrub will bloom pink unless a soil acidifier is applied. Always follow the application rates on the package and repeat at the recommended time interval until you achieve the colour you are looking for. Be aware that this process can take months or over a year to achieve.

For deep blue blooms, aim for a pH of 4.5, for muted blue, aim for 5, and for violet-blue, aim for 5.5. Be conscientious of any plants around your hydrangea as most of them will prefer neutral or alkaline soil, and applying an acidifier can be detrimental to their health. Also be aware of any concrete sidewalks or driveways nearby as they contain lime which makes it difficult to lower the pH enough to change your hydrangea’s bloom colour.

Remember, no varieties of Hydrangea paniculata, quercifolia, arborescens, and anomala subsp. petiolaris will change colour, regardless of the soil’s pH.

Within the two species of Hydrangea that can alter their bloom colour, there are specific varieties that are more sensitive to pH changes and therefore change the colour of their blooms more easily.

The following are varieties of Hydrangea macrophylla that will turn blue the easiest:

• Let’s Dance ‘Rhythmic Blues’
• Let’s Dance ‘Blue Jangles’
• Endless Summer ‘The Original’

The following are varieties of Hydrangea serrata that will turn blue the easiest:

• ‘Twist and Shout’
• ‘Tiny Tuff Stuff’
• ‘Tuff Stuff Ah-Ha’
• Let’s Dance ‘Starlight’