Question
I am adding aluminum sulfate to my hydrangea bed (around plant drip lines) to change color to blue. All of my plants already have very large bloom heads and are very bright magenta pink. I sprinkled a couple tablespoons of aluminum sulfate around each plant and was just wondering how long it normally takes to start seeing the change in color and will it affect the current blooms?

Answer
Hi Shanna, I've seen them change within a couple of weeks, but I think you need to add more.  I'd add 1 to 2 cups for a 3' tall plant.
Also, use a low phosphorous fertilizer on them.  Phosphorous can lock up the aluminum, which is what makes them blue.  Jim