The trick to turning the flowers of hydrangea bushes blue is to make the soil more acidic. The reason behind this is that hydrangeas are sensitive to soil pH levels, and the color of their flowers can be influenced by the acidity or alkalinity of the soil.

To turn the flowers blue, you need to lower the pH level of the soil to around 5.2 to 5.5. One way to do this is to add aluminum sulfate to the soil, which will increase the acidity of the soil and make the flowers turn blue. You can apply aluminum sulfate to the soil around the base of the hydrangea bushes in the spring, and then water it in thoroughly.

It’s essential to note that this method works best on hydrangea varieties that produce blue flowers naturally, such as the big-leaf hydrangea (Hydrangea macrophylla). Other varieties, such as the white-flowering Annabelle hydrangea, do not respond to soil acidification and will not turn blue.

It’s also important to be careful not to overdo it with the aluminum sulfate. Too much can burn the roots of the plant and harm the hydrangea. Therefore, it’s a good idea to test the soil pH before adding anything to it and to follow the application instructions carefully.

There are several methods that can be used to turn hydrangea flowers blue:

1. Acidify the soil

As mentioned earlier, the color of hydrangea flowers can be influenced by the acidity or alkalinity of the soil. To turn hydrangea flowers blue, you can acidify the soil by adding aluminum sulfate, sulfur, or other acidifying agents to the soil. This will lower the pH level of the soil, which will make the flowers turn blue.

2. Use acidifying fertilizers

You can also use fertilizers that are specifically designed to acidify the soil, such as those that contain ammonium sulfate or urea. These fertilizers will not only provide nutrients to the plants but also help to lower the soil pH, which will turn the flowers blue.

3. Add coffee grounds

Coffee grounds are acidic, and they can be added to the soil around the base of the hydrangea plant to lower the soil pH. This method can take some time to have an effect, but it is a natural way to turn the flowers blue.

4. Use rainwater

Rainwater is naturally acidic, and using it to water your hydrangea plants can help to lower the soil pH and turn the flowers blue. You can collect rainwater in a barrel or container and use it to water your plants.

It’s important to note that not all hydrangea varieties can be turned blue. The color of the flowers depends on the genetics of the plant, and some varieties will always produce pink or white flowers, regardless of the soil pH. The most effective way to turn hydrangea flowers blue is to choose a variety that naturally produces blue flowers.