Blue or Pink - Which Color is Your Hydrangea
FOR IMMEDIATE RELEASE
June 18, 2013
The hydrangeas are beginning to bloom and show their colors.
Beautiful pinks, blues, whites, greens – there are a number of different
species of hydrangea to choose from. You
may have even seen a beautiful Nikko Blue Hydrangea but when it's planted
somewhere else, it blooms pink instead of blue. So what happened? It's the same plant – but just planted in a
The colors of the blooms for those hydrangeas that are
supposed to bloom pink or blue are directly connected with the pH of the soil
they are planted in. The hydrangeas directly affected by the pH are Bigleaf
Hydrangeas – Hydrangea macrophylla. Aluminum is what causes the flowers to turn
blue and typically there is enough aluminum in the soil, but the pH can lock up
the aluminum particles in the soil making them unavailable to the plant. It should be said that there are a few
varieties of Bigleaf Hydrangeas that have mostly white flowers and are tinged
with color or shift to another color as they mature – and these can still be
affected by soil pH. In fact there are some pink blooming Bigleaf Hydrangea
like 'Pink Elf' and 'Glowing Embers' that can never turn blue and may only turn
a purplish color.
To put it simply – acidic soils will cause Bigleaf
Hydrangeas to bloom blue and alkaline soils will cause the plant to produce
pink flowers. You can find out the pH of your soil by sending in a soil sample
to a soil testing lab. When looking at your soil test – a pH of 7 is neutral,
below 7 is acidic, and above 7 is alkaline.
That is the common breakdown of soil pH, but when we starting looking
into soil pH for hydrangeas, the ranges where flower color is impacted shift a
bit. It's not a simple above 7 or below 7.
For hydrangeas – soil pH below 5.5 will cause flowers to be blue, pH
above 6.5 will be pink and typically if the pH is between 5.5 and 6.5 we can
see a melding of the two colors bringing it closer to a pinkish-purple colored
If you wish change the color of your Bigleaf Hydrangea, you
can do so by applying aluminum sulfate or sulfur to lower soil pH or limestone
to raise pH . Sulfur is a safer bet when trying to lower pH as sulfur reduces
the chance of aluminum toxicity that can occur from using aluminum sulfate. Assume
that changing the color of your hydrangea is a gradual process – it's not
necessarily going to be immediate, it may take a few years. Patience is key
when it comes to influencing hydrangea flower color. Whatever you are using to
influence the color of the flowers, make sure to apply according to the label
and only use the recommended amounts. Some basic recommended guidelines are 1/2
cup of wettable sulfur (lower pH) or 1 cup of lime (raise pH) per 10 square
With Bigleaf Hydranageas it is also a good idea to know if
they bloom on old or new wood. Sometimes
late frosts can damage buds that formed on previous year's wood. With Bigleaf Hydrangeas that bloom on new and
old wood can provide a longer bloom time – varieties such as 'Endless Summer'
and 'All Summer Beauty' bloom on old and new wood.
Hydrangeas are high impact plants for full sun to partial
shade locations and by providing evenly moist, well-drained soil can provide
you with summer long color.
Source: Kari Houle, Extension Educator, Horticulture, firstname.lastname@example.org