what makes hydrangeas purple?

Hydrangeas are one of the few plants that change color like that. My Nikko blue hydrangea was, until this year, a nice rich pink.

How acidic or alkaline the soil is determines the color of the hydrangea, and a maturing flower will tend to change color as well. An acid soil produces a blue flower, an alkaline soil produces a pink flower. Purples tend to happen at the slightly acid side where both blue and pink are being produced in the flowers.

A lot of sources suggest using aluminum sulfate powder to change the color of the hydrangea. Aluminum can be toxic to plants, so using too much would be a bad idea. I altered mine to blue by using ferrous sulfate instead, which dropped the pH and raised the amount of available aluminum without risking soil damage.

Don't use a high-phosphorus food with most hydrangeas as that will force the colors toward pink even in slightly acid soils.

My grandmother used to place nails around hydrangeas to produce pink blooms. According to one of my gardening books, you can raise acidic level by applying acidic peat or acidic mulch made of pine needles. Use a fertilizer that promotes acid-loving plants which will creat reactions that lower soil pH. You can also apply ordinary powdered sulfur to correct alkalinity, but you must strictly regulate the reate of application according to your soil's needs. You can also use commercial aluminum sulfate instead of powdered sulfur. I would be careful and add minimum amounts until you get the change in color. I'm fortunate I guess, my plants have such a beautiful, deep, deep purple color. I've been tempted to try and play with the color, but afraid I'll mess up and kill the plants.... good luck though

I have heard that you put iron in the ground to make them change. I recall burying an iron spike from the railroad tracks. I have no idea if it worked because I forgot that I did it until just now and that was long long ago. I'm sure you can find the information your looking for online.

They respond to the alkaline or acid content in the soild. One (I think acid )makes them blue or bluish purple. the other makes them pink, or vice versa. Apparently they are unique in their response to the ph balance in the soil

alkaline or limey soil makes them go blue neutral soil makes them go white and acid makes them go pink, some varieties have slight differences in its case acidic soil makes reddy purple and limey soil Will make them bluey purple

The soil that you have it growing in if you like the color put some coffee around it