How to Change the Color of Your Hydrangea Blooms

You can decide what color your hydrangeas are - ravishing pink or bright blue, and it's pretty easy! Join our gardening expert Debbie as she explains the science behind the process and offers tips on how to change the color of your hydrangeas from pink to blue, or from blue to pink.


Hi, I'm Debbie with Spring Hill and today, we're going to talk about how you can change the color of your hydrangea. You may have heard a bit about this, about going from pink to blue or from blue to pink. Well, the key is all in the pH of the soil. If you want to change your hydrangea to blue, what you'll do is, you'll make your soil more acidic by adding aluminum sulphate. And if you want them to turn pink, you'll do the exact opposite by making it more basic, by adding some lime. So, how does all this work anyways? Let's find out. Alright, well, we're all going to take a trip back to elementary school science class. Anybody remember the vacuole? The vacuole is the storage organ in the petal which stores, among other things, color. So, in a hydrangea, to produce the color blue, the vacuole needs aluminum. So, this is where the pH comes into play. By turning the pH acid, or adding aluminum sulphate, you're doing two things. First of all, the sulphate mixes with the water in your soil to create H2SO4 which is Sulphuric acid. What that does, it creates more acidity in your soil, but it also releases the existing aluminum in the soil. Lets the roots absorb them so that they can be transported up to the vacuole. Now of course, you're also adding some more aluminum in the aluminum sulphate, so you're giving your vacuoles or your petals a double dose of blue. Now on the flipside of it, when you add lime, you're doing the exact opposite. You're taking the aluminum that's in the soil and you're binding it up so that it can't produce blue. Of course, when there's no blue, you're just going to see more pink. So, there you go, that's how you change the color. Now keep in mind that you can only manipulate color when there's color to begin with. And of course, we all remember from science class that white is the absence of color. So, this isn't going to work with white hydrangeas, it will only work when there's already some existing blue or pink. Now if you really want to get scientific, get yourself a pH tester. That will tell you what your baseline is in your soil. As you can see from ours, we have a little bit of pink and a little bit of blue. So next spring, I'm going to pour on a ton of aluminum sulphate and see if we can't turn these hydrangeas bright blue. So, I'll see you back next year.