The color of the lush inflorescences of the hydrangea is an exciting topic, because you can influence this color yourself with simple means. An originally pink colored hydrangea will change flower color to blue or purple depending on how acidic or alkaline the soil is.

Deep purple hydrangeas

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

floor PH value
humus 4,0 - 5,0
Peat soil (peat) 3,8 - 4,3
rhododendron soil about 4.5
sandy soil below 4.4 or above 8.8
Sandy soil with little clay 5,5 - 6,2
sandy loam 6,3 - 6,7
potting soil 6 - 7
clay soil 6,5 - 7,2

If you have planted the hydrangea in a rather alkaline soil, the flowers will show a pink colour. On the other hand, if the garden soil is acidic, the flowers will 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.

Dye hydrangeas purple in a targeted manner

Consequently, if a purple hydrangea turns back to pink, you need to add aluminum sulfate (potassium alum, alum) to the hydrangea and acidify the soil.

To make the soil type more acidic, you can

  • compost
  • composted foliage
  • rhododendron earth

incorporate into the subsoil. For ecological reasons, peat should only be used in exceptional cases.

You can administer the aluminum sulphate or alternatively hydrangea blue 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 will turn a pink hydrangea purple, although this is not always desirable. Here, too, you have the option of specifically influencing the color of the flowers.

First of all, it is important to shift the pH of the soil into the alkaline range. Lime the soil around the hydrangea several times a year and measure the pH value at regular intervals. It should ideally level off at around 6.2. You can also fertilize the hydrangea for a while with a standard flower fertilizer (€1.95). This contains more phosphorus than special hydrangea fertilizer and thus inhibits the hydrangea's aluminum absorption, which is responsible for the unwanted colouration.

tips and tricks

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

Category:

Vegetable garden