How to have blue hydrangeas?

How to have blue hydrangeas?

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A color that depends on the earth

First of all, you need to choose a variety of hydrangea capable of giving blue flowers. And for that, you must be interested in the nature of your earth and more generally in the geology of your exterior. Indeed, the blue color of hydrangeas depends mainly on two factors:

  • The acidity level of the soil: blue hydrangeas grow in acid soils. Grown in basic soil, they will be pink. In other words, they change colors according to the pH of the earth. A pH between 4.5 and 5.5 allows you to get blue flowers. To keep a pink color, the pH of the soil must be higher than 6.
  • The absence of limestone : most hydrangeas cannot tolerate lime. Not only does it slow down their development, but it can also favor the appearance of diseases. If your soil is rich in lime, plant your hydrangeas in pots and avoid watering them with tap water.
  • The presence of aluminum in the soil: or more exactly aluminum sulphate or alumina because they are the ones that make the petals turn blue. It is in regions where the soils come from shale rocks, that blue hydrangeas flourish the most. This is particularly the case in Brittany, Normandy and the Basque Country.

Good to know: only pink or purple hydrangeas can make blue flowers appear. The white and red varieties are not able to change shades.

How to get blue hydrangeas?

If it is unthinkable to get blue flowers without the elements mentioned above, there are a few tips to maintain the blue color of hydrangeas. Start by testing the nature of your soil in order to make readjustments if necessary.

To make your hydrangeas turn blue and make the color last in a low aluminum soil, you can incorporate alum (aluminum sulphate powder) or even crushed slate and iron sulphate in the ground. Regarding the pH of the soil, you must bring it additional sulfur or acid compost if the pH is too low.

If you are looking for natural alternatives, nothing prevents you from betting on organic materials. We think in particular of coffee grounds, which can, with a little patience, modify the pH of the soil. Add fruit and vegetable waste and cut grass for even more efficiency. In any case, avoid watering your blue hydrangeas with hard water. You can filter it or even better, collect rainwater.