How to Change Colour of Hydrangea- Hydrangea Color pH Chart

Learn how to change colour of hydrangeas and hydrangea colour pH chart to get blue, pink or red hydrangeas. Hydrangea flower clusters can vary in colour in shades of blue, pink, purple, pink and several shades in between. But how to modify the colour of your hydrangea to get blue or pink colour?

Follow the simple steps on changing the colour of hydrangea to blue or pink
Blue Hydrangea Flowers
Blue Hydrangea Flowers

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How To Change Hydrangea Colours : Hydrangea Colour pH Chart

Changing the colour of hydrangea depends on two factors:
  1. The amount of light and the shade the plant receives will affect flower colour. Two identical hydrangea plants planted next to each other, one in shade and one in partial shade can have flowers of different tones of colour, even green hydrangeas. However, it is not possible to get red hydrangeas by simply changing the soil pH. However, the white hydrangea color is not affected by the soil pH.
  2. The pH of the soil: The acidity of the soil (i.e. its pH) determines the colour. The chemistry of the soil gives a measure of hydrangea color change. Following chart is a guide for hydrangeas colour on soil pH:
Soil pH Chart
Hydrangea Colour pH Chart
  Hydrangea Colour pH Chart
  pH      Colour
  4.5      Deep blue 
  5.0      Medium blue 
  5.5      Lavender purple 
  6.0      Purple pink 
  6.5      Light pink 
  6.8      Medium pink 
  7.0      Deep pink 

So it is possible to change the colour of flowers simply by changing the acidity of the soil according to the colour pH chart. A soil pH of 4.5 will make hydrangea deep blue, while a pH of 7 will turn hydrangea colour to deep pink or red. 

As most garden soils are alkaline so the flowers will be pink. Changing a hydrangea from blue to pink is difficult than changing from pink to blue.

You should have patience because hydrangea colour changes will not occur overnight. Control over the colour of hydrangea in ground is difficult than for potted plants.

To change the pink colour of my hydrangeas to blue, I planted my hydrangeas in pots with azalea potting mix. I also added lot of rotten leaves and aged compost into it. I fed the plant with fertilizers suitable for azaleas.

There are some techniques to reduce the acidity or pH of soil to modify the hydrangeas.

How To Get Blue Hydrangeas

  1. If your soil is highly alkaline, it is impossible to turn a hydrangea blue for ever.
  2. Do not plant your hydrangeas near a wall because the soil pH may be raised by lime leaching out of the wall, making it difficult to obtain blue.
  3. It would be better to grow them in large pots where it is much easier to control the requirements for turning the flowers to blue.
  4. Add lots of compost, rotten leaves, coffee grounds, fruit and vegetable peels and grass clippings to bring the pH down. You may use potting mix and fertilizer for azaleas
  5. The Coffee grounds add acidity to the so, which makes it easier for the roots to absorb naturally occurring aluminium in the soil. The effect is blue clusters of flowers.
  6. Adding Epsom salt in the soil will not change the colour of hydrangea blooms.
  7. The pH of the water from your tap should not be higher than 5.5. It is a better idea to have your water tested. A dilute vinegar solution may help.
  8. A fertilizer high in potassium and low in phosphorus and nitrogen is helpful in producing a good blue colour. Do not feed your plant bone meal and super-phosphates. You can give banana peel fertilizer, which is high in potassium.
  9. Adding aluminium sulfate will help change colour. In acidic soil, the roots takes aluminium from the soil and change the pigment anthocyanin which gives pink colour to the flowers to blue pigment to form the blue version of hydrangea. Apply a solution of 1/2 teaspoon aluminium sulfate in 1 litre of water to the plant throughout the growing season. It is important to water the plant before applying the solution to prevent roots from burning.
  10. Rack some steel wool near the roots to make blue flowers more deep.

How To Get Pink Hydrangea

Pink Hydrangea Flowers
Pink Hydrangea Flowers
  1. For hydrangea blooms to be pink, the plants must not take up aluminum from the soil or you have to raise the soil pH. If the soil of your garden is acidic you should plant hydrangeas in large pots.
  2. For this add dolomite lime (2-3 tablespoon) into the soil around the roots of the plant several times. The exact amount of lime will depend on soil.
  3. If you add crushed eggshells in the soil, it will reduce the acidity of the soil, making it harder for hydrangeas to absorb aluminium. So the colour will not change to blue.
  4. Adding some baking soda in the soil can change the pH of the soil, which can change the hydrangea colour!
  5. To get pink hydrangeas, feed with a fertilizer high in phosphorus.

Video on Changing Hydrangeas Colors

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