If certain soil conditions prevail, naturally pink hydrangeas turn blue. This is due to the pH value of the soil, which must be in the acidic range. Only then can the hydrangea absorb enough aluminum sulfate from the subsoil. In the following article we will explain how you can influence the condition of the soil so that the hydrangea blooms blue permanently.
How to dye hydrangeas blue?
To turn hydrangeas blue, they need acidic soil (pH below 4.5) and aluminum. Swap the soil for hydrangea soil, lower the pH with compost or vinegar water and add hydrangea blue or potassium alum to the irrigation water. Use soft rainwater for watering.
Acid soil as a basic requirement
In order for the hydrangea to absorb the trace elements from the soil that are responsible for the blue color, it must have a pH value of less than 4.5. However, only a few garden soils are so acidic.
Remedy
- Replace the topsoil with special hydrangea or rhododendron soil when planting the hydrangea.
- Analyze the pH value regularly with test strips from garden shops.
- If this value is too high, it can be reduced by adding a small amount of composted leaves or mature compost.
- Watering with vinegar water also lowers the pH value.
Watering water
Limiting shifts the pH value of the soil towards alkaline and the hydrangea loses its beautiful blue color. Therefore, in regions with hard water, water the plant only with soft rainwater.
How to dye a hydrangea blue
For a pink hydrangea to turn blue, acidifying the soil is usually not enough. In addition, you must add the aluminum responsible for the blue color to the earth.
You can either add commercially available hydrangea blue (€11.00 on Amazon) or alternatively potassium alum to the watering water. To protect the environment, please follow the instructions on the packaging.
Discoloration occurs slowly
It can take up to two years for the hydrangea to turn completely blue. At first, attractive intermediate tones such as violet or a blue-tinged pink appear. Usually even the flowers of an umbel are shaded differently, which gives the plant a special charm.
Tips & Tricks
The rumor keeps circulating that coffee grounds and ground eggshells as fertilizers turn hydrangeas blue. In fact, eggshells add calcium to the soil. Coffee pomace improves the soil structure and shifts the pH value slightly into the acidic range. However, these measures alone are only sufficient if the garden soil is relatively acidic anyway.