Pink or blue blossoms?
Which Type of Hydrangeas Change Color?
Hydrangea flowers, in general, come in beautiful shades of white, blue, pink, red, purple, and green.
However, the only hydrangea variety in which you can change their flower color is the Bigleaf hydrangea
(Hydrangea macrophylla), also known as French, mophead, lacecap or mountain hydrangea (H. serrata).
You can change their flower color from pink to blue and vice versa by raising or lowering the pH of the soil.
The determining factor of hydrangea color is the level of soil acidity: in alkaline soil, hydrangea flowers
turn pink, but in acidic soil, they turn blue. The soil in our area is, generally, alkaline which gives us
pink flowers. The soil on the East Coast that produces the beautiful, blue-flowered hydrangeas is acidic.
How Do You Change the Flower Color?
You must gradually amend the soil* by following the steps below:
1. Do a Soil Test
A soil test to determine the pH of your soil is the best way to know whether you need to increase or decrease the pH to achieve the desired flower color. For the most accurate results, use a soil pH testing kit available at Pasquesi.
*Adding amendments to the soil based on merely guessing the soil pH can harm, not only the hydrangea, but also other plants in the vicinity.
2. Select Your Soil Amendment
To turn the flowers blue, you must lower the soil pH (making it more acidic) by adding aluminum sulfate (Bonide Garden Rich Aluminum Sulphate) or wettable sulfur to the soil (Espoma Organic Soil Acidifer). Or, to turn the flowers pink, raise the soil pH (make it more alkaline) by adding limestone to the soil (Bonide Garden Rich Hydrated Lime). The exact amounts of aluminum sulfate, sulfur, or lime that you’ll need depends on the soil pH and soil type. Carefully follow the directions on the package and don’t use more of the product than indicated because it will injure the plant.
3. Use Granular Products or the Liquid Drench Method*
Granular products such as Espoma Organic Soil Acidifier can be applied at any time of the year. Apply the product around the base of the plant and work it into the soil with a rake or trowel. It can take up to a year for the soil pH change to take effect and change the flower color of your hydrangea. Gradual application is best.
*A quicker way to change flower color is through liquid soil drenches applied in March, April and May. Begin in early spring to make the flowers turn blue. Dissolve 1 tablespoon of aluminum sulfate (Bonide Garden Rich Aluminum Sulphate) into 1 gallon of water. Water the soil around the plant with this solution. Avoid getting it on the leaves.
FYI... Changing the soil pH is a gradual process that cannot be done all at once. And, even if you can get the soil to the desired pH, it will naturally revert to its original soil pH over time, so changing the flower colorof your hydrangea is a constant process. Many times, the continual application of wood, pine & leaf mulches will add to the acidity of the soil around hydrangeas and contribute to blue flowers over time.