How To Keep Hydrangeas Blue (Or Pink)

Blue & Pink Hydrangea

If I have pink hydrangeas my customers want blue, and if I have blue they want pink. So I always say why don’t you change the colour once you have planted the hydrangea in your garden, to this I always get a very puzzled look from the customer.

Most blue and pink hydrangeas especially the mop-head variety can do a colour changing trick, or you may wish to keep it the original colour when purchased but have noticed that it’s starting to change colour.

The only colour hydrangea that can’t be changed is white.

The colour of your hydrangea is determined by the pH level of the soil that it is planted in. If it’s in acid soil it will be blue, planted in alkaline soil it will be pink. If your hydrangea is in neutral soil it will have a mixture of pink and blue blooms.

How To Keep Hydrangeas Blue

Blue Hydrangea

To keep your hydrangea blue or if you wish to change from pink to blue it needs to be grown in acid soil that has a pH level of 5.2 to 5.5.

To make your soil more acidic you can add sulphur, aluminium sulphate or sulphate of iron to your soil.

If you are worried about damaging your plants by making the soil too acidic then sulphur is the least likely to harm your plants (and it’s the cheapest).

Your soil can also be made more acidic by applying an organic mulch, such as pine bark or needles.

How To Keep Hydrangeas Pink

To keep it or change it to pink your hydrangea needs to be grown in alkaline soil that has a pH level of 6.5 and above.

The most common way to make the soil more alkaline is to add lime. The best time to do this is in the autumn as it takes several months for the effects to take place.

How To Turn Hydrangeas Purple


I said before that if you grow hydrangea’s in neutral soil you will get a mixture of pink and blue blooms, but some will produce purple blooms depending on which variety you have planted in your garden.

How To Turn Hydrangeas Red

If you fancy turning your hydrangea red then you need to ramp up the alkaline level of your soil. The more alkaline the soil the rosier your blooms will be.