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Hydrangea Flower Colours: Unveiling the Power of pH Levels

Hydrangeas, with their stunning and vibrant blooms, have long captivated the hearts of gardeners. While their natural hues are awe-inspiring, did you know that you can actually change the colour of hydrangea flowers? It’s true! By adjusting the pH levels of your soil, you can transform the shades from blue to pink and vice versa. This article will delve into the fascinating world of pH and its profound impact on hydrangea flower colours. Whether you’re a beginner or an intermediate gardener, get ready to unlock the secret to achieving your dream hydrangea palette.

Understanding pH:

Before we dive into the specifics of changing hydrangea flower colours, let’s briefly explore what pH actually is. pH is a measurement of how acidic or alkaline a substance is on a scale of 0 to 14. A pH of 7 is considered neutral, below 7 is acidic, and above 7 is alkaline. The pH of your soil plays a crucial role in determining the availability of nutrients to plants and can even affect their overall health and vigour.

The pH Scale
The pH Scale

Hydrangeas and pH Sensitivity:

Hydrangeas are unique in their sensitivity to soil pH. This sensitivity is closely linked to the availability of aluminium ions in the soil. When the soil pH is acidic (pH below 7), hydrangeas absorb aluminium more easily, resulting in blue flowers. Conversely, in alkaline soil (pH above 7), aluminium becomes less accessible, causing hydrangeas to produce pink or even shades of red blooms. The pH level of your soil is thus a key factor in controlling the colour of your hydrangea flowers.

Changing Hydrangea Flower Colours:

Blue Hydrangeas:

To achieve those breathtaking blue hues, you’ll want to create acidic soil conditions with a pH below 7. Here’s how:

  1. Test the pH of your soil using a reliable pH test kit. You can find these kits at your local gardening centre or online. Ensure you follow the instructions provided carefully.
  2. If your soil pH is already in the desired range, you’re all set! Blue hydrangeas should thrive in your garden. If not, proceed to the next step.
  3. To increase soil acidity, you can add aluminium sulfate or sulfur. These amendments will help lower the pH gradually. Apply them according to the package instructions, as over-application can harm your plants. Remember to water your hydrangeas thoroughly after adding amendments.

Pink Hydrangeas:

For those longing for romantic pink blossoms, you’ll need to create a more alkaline soil environment with a pH of above 7. Follow these steps:

  1. Begin by testing the pH of your soil, as mentioned earlier.
  2. If your soil is already within the desired pH range, your dream of pink hydrangeas is within reach. Proceed to planting and caring for your plants. If not, continue to the next step.
  3. To raise soil alkalinity, you can add lime to your garden bed. Lime can be applied according to the package instructions, but remember not to overdo it. Be patient, as it may take time for the pH to adjust. Adequate watering is essential after applying lime.

Maintaining Optimal pH Levels:

Once you’ve achieved your desired hydrangea flower colour, it’s essential to maintain the appropriate pH level in the long run. Regularly monitor your soil’s pH, especially if you observe any changes in your hydrangeas’ colouration. By doing so, you can take timely actions to correct any deviations.


With a little knowledge and effort, you can transform your hydrangea garden into a captivating display of colour. By understanding the correlation between pH levels and hydrangea flower colours, you have the power to create the exact floral palette you desire. Remember to test your soil’s pH, make necessary amendments, and provide appropriate care to ensure healthy and vibrant hydrangeas.

Updated on November 3, 2023

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