Q.Is there a way to get light blue hydrangea flowers to turn a deeper/darker shade of blue?
I know that changing the acidity of soil allows you to turn hydrangea flowers from pink to purple to blue. However, I notice that some shrubs in my neighborhood have light blue flowers (such as my hydrangea), while others have a deeper, darker shade of blue. I see the same within pink and purple varieties—variations in color saturation as opposed to the color itself. Is there a way to control this or encourage deeper colored flowers? Or does it depend on the plant variety?
Certified GKH Gardening Expert
This Extension fact sheet says adding aluminum sulfate to the soil will make the blues darker.