What should I do to make my Hydrangea's change color.

Coffee grounds

what color is the hydrangea and what color do you want

I've never tried coffee grounds, but I do know the colors are a result of acidic soil vs. alkaline. Acidic soil yields blue flowers. Alkaline yields pink. You can buy a soil tester at Lowe's for under $10. If you want blue flowers and need to up the acid in your soil, add sulfur. If you want alkaline for pink flowers, add lime. Good luck!

I have read of folks who acidified one side of the hydrangea and alkalynized the other for a bi-color effect.

Put some pennies in the soil around the base of your plant. The copper in them helps to turn the color blue.

use akaline

meant alkalyn