How to get and keep blue hydrangeas

(To be incorporated only if you want to obtain blue and mauve hydrangeas).

You will find this amendment under the term “Bleu de Bretagne”. In an appropriate substrate, this composition will be more easily assimilated by the root system of hydrangeas. It will allow you to obtain or maintain the blue, mauve, or garnet color. If your land’s parent rock is not of slate type, the implementation of a substrate and the application of aluminum sulfate Al₂(SO₄)₃ must be carried out to obtain bluish colors.

Initially, it will be important to add “Bleu de Bretagne” to your pre-planting mixture. Subsequently, application should be done as a top dressing. Doses will be indicated on the packaging or instructions. You can obtain blue hydrangeas even more easily if you cultivate them in pots. Iron sulfate can also be added during the aluminum sulfate application to better acidify your substrate and promote aluminum dissolution by water.

To better understand, it should be known that metamorphic slate-type rock is chemically composed of approximately 30% alumina. This rate is of course variable depending on different regions with this parent rock. It is the aluminum present in the sheets of this rock that allows the blue coloration.

In France, slate-type parent rocks are present in the Brittany region (Finistère, Morbihan, and Côtes-d’Armor) as well as in certain areas of the departments of Maine-et-Loire, Mayenne, Corrèze, Hautes-Pyrénées, Savoie, Ardennes, and Tarn.

It should be known that regarding hydrangeas, there are no specific varieties (even new varieties) that are blue in any type of soil.