You chose it for its beautiful deep blue color, but surprise, once installed in your garden for some time, your blue hydrangea has turned into pink. Did the fairies of 'Sleeping Beauty' come to you? No way! Let's see how to give it back its original colors.
Mysteries of Nature
Hydrangea macrophylla, better known as the florist's hydrangea, is a spectacular flowering plant, as much for the rounded size of its inflorescences as for its colors. Some varieties have a variable flower color passing strangely from blue to pink. There is no mystery behind this, it is simply a physical phenomenon that comes into play in the color of the flowers: the pH and the composition of the soil.
In a soil with an acidic tendency, the flowers remain blue or are purple if the variety chosen was it at the base.
In a calcareous soil with a pH higher than 7, the color turns spontaneously to pink, or even to red if the variety allows it.
Another parameter concerning the soil, the iron and aluminum content in their assimilable forms must be sufficient. Knowing that in calcareous soil, iron is very poorly assimilated by plants, everything is explained...
How to maintain the blue color in hydrangeas?
As we have seen, the color varies according to the pH of the soil. It is therefore obvious that it will be a little complicated to maintain a beautiful blue color in calcareous soil. However, here are a few ways to help:
- Apply a fertilizer rich in potash and alum in August when the future flower buds are forming to prepare for the next year's bloom.
- Apply every spring and during the growing season a bluing product.
- Be careful with tap water, which, if hard (calcareous) will not suit your hydrangea. Always prefer to water it with rainwater in these conditions.
- When planting, if the soil is chalky, dig a pit of 1 meter by 1 meter and fill it with heather soil, compost and a little dried blood before installing your hydrangea. Each fall, scratch some heather soil on the ground.
- If the soil is very calcareous, prefer planting in a large container in a mixture of heather soil.
- Mulch the base of your hydrangea with a thick mulch of pine bark. This mulch tends to slightly acidify the soil. If you are a fan of mineral mulch, don't hesitate to mulch the base with crushed slate, known to give a beautiful blue color to the hydrangea.
- You can find it in DIY stores or garden centers under the name 'Blueing Fertilizer for Hydrangeas' . These products contain iron sulfate and alumina, in addition to NPK formulations adapted to hydrangeas.
- Remember to water your hydrangeas regularly so that they do not suffer from water shock and so that the roots can synthesize the elements provided.
