How to Change the Color of Hydrangeas

September 30, 2016

Most people would probably 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.

Large deep pink hydrangea blossoms - August summer flower.

pH Levels 101

In scientific terms, a soil’s pH level refers to the acidity or alkalinity of the soil – pH is the units this reaction is measured in. pH levels are measured on a scale from 0 to 14, and soils with a pH of 7 to 0 are considered to be 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 increasingly more difficult for plants to absorb the necessary nutrients from the soil – as you can already see, your soil’s chemistry plays a big role in your 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 within the flowers. To take it a step further, blue hydrangeas get their color as a result of aluminum being abundant, while pink hydrangeas get their color from a lack of aluminum. Hydrangeas whose colors seem to be somewhere in between will usually indicate that some aluminum is present.


So where does pH fall in all of this?

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 typically more available in acidic soils, so hydrangeas planted under these conditions are normally blue. That said, you can likely figure out, then, that hydrangeas planted in soils that have a higher pH level tend to be pink.

Changing the Colors of Hydrangeas

Like we said earlier, you do have some control over your hydrangeas’ color and can actually make it change if you follow the right steps! This is what you have to do:

blue-hydrangeaStep #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. That said, if you want to see your hydrangeas change color right before your eyes, make sure that you’re working with hydrangea macrophylla.

Step #2: Measure the pH level of your soil.

This can be achieved using a simple soil test kit. Remember, if you find that your soil has a pH level of 5.5 or lower, you’ll wind up with blue flowers. If, on the other hand, your soil has a pH level of 6.5 or higher, you’ll wind up with pink flowers. Any soil that has a pH level in between 5.5 or 6.5 will typically see a variation of pink, blue and even purple flowers.

Step #3: Make changes depending on your preference.

If you’re happy with your pH level, great! At that point you can just sit back and watch your hydrangeas bloom over time. However, if your soil has a lower pH level but you want to see 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, you can start by adding some powdered Garden Lime to it; wood ash can also be effective too. On the other hand, if you want to lower the pH of your soil and make it more acidic, try adding ammonium sulfate, aluminum sulfate or a soil acidifier. Some other methods you can try to lower pH is to add oak leaves, coffee grounds or sawdust to the soil.

Step #4: Monitor the soil.

Keep in mind that 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 results you’re looking for!