Hydrangeas are known for their big, fluffy flowers that look incredibly vibrant in summer, and it is surprisingly easy to change their colour if you want to add variety to your garden. Certain types, such as bigleaf hydrangeas, will change colour based on the pH of the soil, so you can naturally make these beautiful plants even more colourful. 

If you want blue blooms, you need to make the soil more acidic, although it is often much easier to turn hydrangeas a pretty pink instead. Bill Hageman, a gardening expert from Grow Organic, explains that all you need to do is use the right fertiliser to turn them pink, as they just need to raise the soil pH.

He said: “Contrary to popular belief, hydrangeas do not need truly alkaline soil to turn pink – they just need soil that is less acidic than for blue flowers. 

"If your soil has a lower, more acidic pH, you can add lime fertilisers such as oyster shell or dolomite to raise the pH to the desired level.”

Garden lime neutralises acidic soil, helps add more nutrients and reduces the amount of aluminium in the ground, which it what causes hydrangeas to turn blue. 

Try to look for a fertiliser that is high in the nutrient phosphorus, as this also blocks hydrangeas from absorbing aluminium, so you get pink or red flowers. 

Phosphorus is the key nutrient needed for flower production, so it can help you get even bigger and more vibrant blooms, which will also make your garden look beautiful. 

Bill said: “Adding a high phosphorus fertiliser can discourage the plants from using the aluminium that is present in the soil. This is why it is much easier to turn a pink flower blue than it is to turn a blue flower pink.”

How to turn hydrangeas pink 

To begin, make sure to test the soil pH with a kit or monitor, which you can get from a garden centre. 

Pink flowers will occur if the pH is between 6.0 and 6.4. However, you do not want to raise the pH above this as it can reduce the amount of iron in the ground. 

If the soil is below 6.4 then simply add your fertiliser to the ground and then make sure to water deeply to dissolve the nutrients and speed up the reaction. 

Be patient, as it can take a full season, or even longer, for hydrangeas to change colour. Just monitor the soil every few months, keep fertilising and watering, and you will have bright pink hydrangeas before long.

It tends to be easier to control soil pH in pots rather than garden beds, so if you are about to plant hydrangeas, consider growing them in a container for quicker results.