WHY HAS MY BLUE HYDRANGEA TURNED PINK?

Why has my blue hydrangea turned pink?

It is hard to resist the intense, cobalt-deep blue blooms of any of the container grown hydrangeas that appear for sale over the summer. However once the flowers have faded, and eight months of delicious anticipation and expectations have passed, the '...as if by magic...' replacement pink blooms can be something of a shock to the system!

Ok, so you purchased gorgeous blue but have ended up with dirty pink. What on earth has gone wrong? Well as it happens it really is down to the condition of the earth, or perhaps it would make more sense to say soil, which has caused the problem.

Why has my blue hydrangea turned pink?

Blue flowers turning pink is a problem most associated with the cultivars of Hydrangea macrocarpa, however it can also be seen to a lesser extent with cultivars of  Hydrangea involucrata and serrata. This colour change is due to the soil pH, which most gardeners will associate with ericaceous plants and the effect pH can have on their ability to take up iron and magnesium. In the case of hydrangeas it is aluminium which is the problem element.

For hydrangeas, aluminum becomes unavailable to them under alkaline conditions and aluminium is required so that the plant can produce (among other things) the blue pigmentation in the blooms. Put simply, hydrangeas will flower blue on acidic soils and pink on alkaline soils.

If you have already purchased blue flowering hydrangea then they can be kept blue by growing the plants in acidic soil of between pH 4.5-5. If the soil is not acidic to start with then consider acidifying your soil by digging in plenty of moss peat or ericaceous compost. You also have the option of purchasing 'hydrangea blueing compounds which works by adding aluminium sulphate to the soils. This increases the available aluminum in the soil as well as acidifying the soil further with the sulphur. Be aware though that if the soil is on chalk or is particularly alkaline this treatment will not work. However it can be very effective solution for improving the flower colour in container-grown plants.

For related articles click onto the following links:
HYDRANGEA MACROPHYLLA
HYDRANGEA QUERCIFOLIA
HYDRANGEA SARGENTIANA
HYDRANGEA SERRATA 'Bluebird'
WHY HAS MY BLUE HYDRANGEA TURNED PINK?