Thursday, November 18, 2021

Our Hydrangeas Are Not Blue

The hydrangeas outside the ‘little house’ (studio) were a mess.
Due to neglect by the resident horticulturalist, they had become tall and straggly. Under pressure from the co driver I gave them a real good haircut, almost a buzz cut, last autumn and this season they have come back bushy and flowering like crazy.
But how come the flowers are pink?
The pH of our soil is around 4.5 ie. acidic which means they should be the more desirable blue. 
Some are trying to be.
The pH scale ranges from 0 to 14. Acid soils have a pH of 6.5 or less. A pH of 7 is neutral. Alkaline soils have a pH of 7.5 or more.
Hydrangeas grow best in soil that has a pH of 5.2-5.5. The soil element that turns hydrangeas blue, is Aluminium. At low pH if Aluminium is in the soil it becomes soluble and more ‘available’ to plants even possibly to the point of being toxic.


Aluminium is typically present in ironstone rich soils and those in which the dominant clay mineral is kaolinite. Sandy soils like ours contain little aluminium so while being strongly acidic, there is little influence on turning the flower colour to blue.
Maybe we could add Aluminium sulphate to the soil but that seems a bit OTT when we are happy with the colour the flowers are.

1 comment:

KrisR said...

They are beautiful! Thanks for giving them a haircut. xo