Hydrangea and Its Changing Colours

(Question)

Hello!
This is my very first-time gardening! I have heard about how hydrangeas can change colour by manipulating the soil pH (like how it can change from blue to pink), and I find this very interesting. However I have many questions about this amazing flower:

How long does it take for a hydrangea to change colour? How many times maximum can I change its colour in the course of its bloom time (if I change the soil pH too many times, will the flower be damaged)?
What is the best method of manipulating the soil pH to get a colour change?
Are there any other flowers that can change colours?

Thank you so much!

(Answer)

Hydrangea macrophylla is indeed an an amazing plant with beautiful flowers.  You are right, the soil pH can determine the colour of the flowers, except for white hydrangeas.

I would recommend that you check your soil pH first with a soil testing kit which is available in most garden centres and hardware stores.  The pH level is a logarithmic scale ranging from 1 to 14 that refers to the potential Hydrogen concentration in the soil. Soil pH determines the availability of mineral nutrients for your garden.  If your soil pH is below 6 (strong acidic soil), the flowers will turn blue.  Alkaline soil which has a pH above 7 will turn the flowers pink.  If the pH is between 6-7, the blooms may turn purple or a mixture of blue and pink.

Changing the soil pH in a garden is not an instant fix.  Soil pH levels develop naturally for your environment.  To make your soil more acidic, you must add garden sulphur, to make it alkaline, add ground lime.  Both products are available at garden centres with instructions for use. It takes about 6 weeks for the bloom colours to change. Changing colours multiple times in a season is not an option.

When using sulphur for changing soil pH the acidifying effect depends on the soil bacteria (thiobacillius), which oxidizes the sulphur and releases diluted sulphuric acid into the soil over a period of weeks to months. Because of this, sulphur must be mixed through the soil to be in contact with these bacteria, otherwise there will be strongly acidic areas around blobs of sulphur and no effect elsewhere in the soil.

As a novice gardener, you might want to try your hand at changing the colour of a hydrangea in a planter, rather than directly in the garden.

Good luck and welcome to the world of gardening!  If you have questions in the future, please do not hesitate to e-mail us again.