Coloring hydrangeas purple or pink - how does it work?

Coloring hydrangeas purple or pink - how does it work?

Bright purple colored hydrangeas

Hydrangeas prefer acidic soils with a pH between 4 and 4.5. Many substrates do not have the optimal values, as you can see in the following table:

also read

  • Pink hydrangeas - the quick-change artists in the flowerbed
  • Hydrangeas: flowers in many different colors
  • Red hydrangeas need the right soil
groundPH value
Bog soil (peat)3.8-4.3
Rhododendron soilabout 4.5
sandy soilbelow 4.4 or above 8.8
Sandy soil with little clay5.5-6.2
sandy loam6.3-6.7
Potting soil6 - 7
Clay soil6.5 - 7.2

If you have planted the hydrangea in a more alkaline soil, the flowers will turn pink. However, if the garden soil is acidic, the flowers turn blue or purple. This is due to the fact that the hydrangea absorbs more aluminum from the acidic soil, which is responsible for the coveted tint.

Color the hydrangeas purple in a targeted manner

If a purple hydrangea turns back to pink, you must therefore add aluminum sulphate (potash alum, alum) to the hydrangea and acidify the soil.

To make the soil type more acidic you can

  • compost
  • composted leaves
  • Rhodondron earth

work into the substrate. For ecological reasons, peat should only be used in exceptional cases.

The aluminum sulfate or, alternatively, hydrangea blue can be administered together with a low-phosphorus fertilizer with a high potassium content.

Turn purple flowers pink again

If your garden soil contains a lot of aluminum and is acidic, it turns a pink hydrangea purple, although this is not always desired. Here, too, you have the option of working specifically on the flower color.

First of all, it is important to shift the pH of the soil to the alkaline range. Lime the soil around the hydrangea several times a year and measure the pH at regular intervals. Ideally, it should level off at around 6.2. In addition, you can fertilize the hydrangea for a while with a commercially available flower fertilizer (€ 13.27 on Amazon *). This contains more phosphorus than special hydrangea fertilizers and thus inhibits the hydrangea's aluminum absorption, which is responsible for the unwanted color.

Tips & Tricks

You can measure the pH value of the soil with test sticks from a gardening specialist. These measurements should be carried out at regular intervals, as rain and irrigation water can shift the pH value back into the alkaline range.