How to Change the Color of Hydrangeas

Most people would agree that plants and flowers bloom in certain colors, because, well, they just do. And while this may be true for some plant and flower species, one in particular that you have some control over (and can even change) is hydrangeas. How so? It all has to do with your soil.

pH levels 101

In scientific terms, a soil’s pH level refers to the acidity or alkalinity of the soil; "pH" is the units in which this reaction is measured. PH levels are measured on a scale from 0 to 14; soils with a pH of 0 to 7 are considered more acidic, while a pH of 7 to 14 labels soil as being more alkaline.

Generally speaking, a pH of 6 to 6.5 is ideal for plants to access the nutrients they need. When pH levels are too high or too low, it makes it harder for plants to absorb the necessary nutrients from the soil. So, a soil’s chemistry plays a big role in plants’ survival.

pH levels and hydrangeas

For hydrangeas specifically, the difference in color from plant to plant has to do with how much or how little aluminum compound is found in the flowers. To take it a step further, blue hydrangeas get their color as a result of aluminum being abundant, whereas pink hydrangeas get their color from a lack of aluminum. Hydrangeas whose color is somewhere between indicates that some aluminum is present.

Where does pH come in?

Ultimately, a soil’s pH level impacts a hydrangea’s color because it affects the amount of aluminum that is available in the soil. Aluminum is more abundant in acidic soils, so hydrangeas planted under these conditions are normally blue, and hydrangeas planted in soils that have a higher pH level tend to be pink.

Changing the color of hydrangeas

Interested in learning how you can change the color of your hydrangeas? Follow these four steps.

Step 1: Check that your hydrangeas can actually change color

Not all hydrangeas produce the same type of flower, and some varieties will only produce one color. For example, Annabelle hydrangeas will only bloom white or cream flowers. So, if you want to change the color of your hydrangeas, make sure you’re working with hydrangea macrophylla.

Step 2: Measure the pH level of your soil

You can measure the pH level of your soil using a simple soil test kit. Remember, soil with a pH level of 5.5 or lower will produce blue flowers, and soil that has a pH level of 6.5 or higher will give you pink flowers. With a pH level of between 5.5 and 6.5, you will typically see a variety of pink, blue, and even purple flowers.

Step 3: Make changes depending on your preference

If you’re happy with your pH level, great — just sit back and watch your hydrangeas bloom over time. However, if your soil has a lower pH level but you want to pink flowers instead of blue (or vice versa), there are a few ways you can go about manipulating the soil.

For example, if you want to raise the pH of your soil, start by adding some powdered Garden Lime to it; wood ash can also work too. If you want to lower the pH level of your soil and make it more acidic, add ammonium sulfate, aluminum sulfate, or a soil acidifier. Some other methods you can try to lower pH is adding oak leaves, coffee grounds, or sawdust to the soil.

Step 4: Monitor the soil

The process of changing your hydrangeas’ color won’t happen overnight, so you’ll need to continue to monitor your soil and treat it as necessary to produce the desired results.