Hydrangeas – Why is my pink Hydrangea blue?

Hydrangea macrophylla ‘brestenburg’, blue hydrangea

Hydrangeas – a popular flowering garden shrub; but one that confuses by changing flower colour after you’ve planted it.

So can you change it back?


Hydrangea macrophylla, also known as mop-head hydrangeas, are the shrubs most often found in gardens. They’re called mop heads due to their round balls of flowers.


By contrast, lace cap hydrangeas small fertile flowers surrounded by larger sterile sepals.

These hydrangeas will very probably change colour according to your soil pH. The reason is not purely down to the acidity of the soil, but the effect this has on the levels of aluminium in the soil.

lace cap hydrangea, holehird gardens


The more acidic the soil, the higher the aluminium levels; which turns pink and purple hydrangeas blue. The cultivars of mop-head and lace cap hydrangeas – macrophylla – are most prone to this effect.

However, if you live on the coast and therefore need one of these salt and shade tolerant shrubs, there is hope.

Before you buy a hydrangea, check the soil pH. The more acidic soil, pH 6 or below should keep it blue flowered.

You can encourage this by mulching your hydrangeas with leaf compost.

Alternatively, plant your mop head hydrangeas in an ericaceous bed filled with a peat free ericaceous compost. If salt tolerance is not an issue, plant your hydrangeas along with rhododendrons and azaleas. Putting all the acid loving plants together will not only keep them happy, but you’ll get a flowering display from April to October.

pink hydrangea flower

Of course if you want a pink hydrangea, you’ll need to have an alkaline soil. If the pH is 7 or above, you should be okay; mulching with spent mushroom compost will help to maintain the alkalinity. If your soil is acid, then grow the hydrangeas in pots, or choose a different type.


Hydrangeas that won’t change colour

Why not make your life easier in the first place, and  choose hydrangeas that won’t change colour when you plant them? Not all hydrangeas have the same flower colour changing tendencies.

White and green flowering varieties tend not to change colour; even in the macrophylla cultivars.

Or choose a different type of hydrangea!

hydrangea petiolaris, Nymans garden

Hydrangea petiolaris

Also known as the climbing Hydrangea. It is a vigorous, self-clinging climbing shrub, grown for its white flower heads.
It takes time to become established but can then become vigorous and may need pruning if it’s not to climb into your gutters!
The dark green foliage turns butter yellow in autumn before leaving a tracery of branches over the winter. The young twigs are an attractive, shiny reddish brown


Hydrangea paniculata

These hydrangeas have cone shaped florets – panicles – up to 8 inches long. Most cultivars flower in late summer and autumn.

Hydrangea paniculata

Hydrangea quercifolia

Huge leaves shaped like oak leaves have red autumn tints; the flowers are white.

Hydrangeas – pruning

Many summer-flowering deciduous shrubs can be pruned between February and early March; usually those that flower on the current year’s growth. Hydrangea paniculata is one of those that require regular pruning.

lilac purple hydrangeas

Mop-head hydrangeas – flower on the previous year’s wood. Deadheading by taking back to a strong pair of shoots can be done in late February if you’re in a mild area, or you can leave until March. Although they do not require much pruning, having a plan that encourages new wood will prevent your hydrangeas from becoming too woody.


Hydrangeas to visit

If you’d like to enjoy hydrangeas en masse, Holehird gardens, home to the Lakeland Horticultural Society has a Hydrangea walk with over 300 species. If you’re not convinced about tthe beauty of Hydrangeas, this is the place to visit in July and August as you’re sure to find a Hydrangea for your own garden.

hydrangeas at holehird gardens

Other parts of the UK with acidic soil often have good displays of Hydrangeas, even if they don’t have the variety of species as offered at Holehird. For example, the shady drive at Portmeirion has glowing hydrangea shrubs outlining your route; very atmospheric. other gardens in Cornwall, the west coast of Scotland and Ireland are worth checking out.


Related Plews gardening blogs you may enjoy: –

Soil – the plant food in your garden
Rose gardens – the scent of paradise
Flowering shrubs for Late Summer Colour
Summer Bedding Plants – Questions and Answers

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