Why do hydrangeas change colour? The trick to use if you want to change bloom colours

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Hydrangeas are very popular plants which are great for late summer colour. They are long-lasting flowers which can be planted in spring and keep blooming until late summer. With June right around the corner, gardeners seeking to change the colour of their hydrangeas should begin the process in a matter of days in order to finish the process in time for next season.

Hydrangeas are a much-loved flower in the UK known for their huge flower heads.

The flowerheads come in a range of shapes, sizes and colours including blue, purple, pink, red and white.

Flowers should grow from around April until October depending on when you planted the flowers.

Many people have a favourite colour of hydrangea – but if you have one colour in your garden and want another, there is no need to fear.

You can actually change some hydrangeas to another colour using a simple trick.

Why do hydrangeas change colour?

Hydrangeas change colour based upon the pH level of their soil.

White hydrangeas will not change colour, but most other colours will.

The more alkaline the soil, the pinker the flowers will be – with highly acidic soil sometimes leading to red shades.

The more acidic the soil, the bluer your flowers will be.

How to change the colour of your hydrangeas

The first step in this gardening process is to test the pH of your soil.

Acidic soil, which means a lower pH level, will yield blue flowers.

You should purchase and use a specialist soil test kit to determine the pH of your soil.

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If you have more alkaline soil and therefore are destined to have pink hydrangeas, but would like blue flowers you should make the soil more acidic.

You can do this by increasing the presence of aluminium.

Add elements such as pine needles, compost, coffee grounds or aluminium sulfate to help make soil more acidic over time.

Bear in mind, you must undertake to change your soil’s pH gradually – it can take up to a year for it to work.

When you have blue flowers, you can turn them pink by removing the aluminium from the soil.

To do this, you should add garden lime or dolomitic lime to your soil to help raise the pH level.

Sprinkle around half a cup of garden lime for each 10 square foot area.

Repeat this process every three to four weeks during the growing season to help keep your blooms pink.

Other things to remember when trying to change your bloom colours:

  • White hydrangeas are not affected by the soil pH.
  • This means they will remain white regardless of the pH level of the soil.
  • Hydrangeas fade naturally and dry in the fall.
  • Hard water may also impact the flower colour so you should try to use rainwater instead of tap water where possible.

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