Can you change the color of hydrangea flowers? It depends on your hydrangea species and the pH of your soil. We will explain how to change the color from blue to pink or from pink to blue.
Which Hydrangeas Can Change Color?
Not every hydrangea changes color. The flowers of some varieties of Hydrangea macrophylla and Hydrangea serrata change color depending on soil pH.
Blue colors are best formed in acidic soil, pink and red are best formed in alkaline or neutral soil. In other words, acidic soils with a pH of less than 5.5 produce blue flowers, and soils with a pH of more than 6.0 produce pink flowers.
Soil pH does not affect the color of white hydrangeas. White flowers remain white (the color can never be changed) and usually prefer the same conditions as pink and red.
But the relationship between color and pH is more complex than just numbers on a scale. It is the presence of aluminum ions and the degree to which a particular variety can absorb them that influences the color of the flowers.
How Long Does Color Change Take?
You can change colors, but it doesn’t happen instantly. Color correction takes weeks or even months to get the desired changes. Blue flowers are easier to change to pink than vice versa, and some varieties are more prone to color variability than others.
We recommend waiting until the plant is at least 2 years old to give it time to recover from the shock of initial planting. Check your soil for pH, and then find out the recommended amount of aluminum sulfate and the appropriate instructions for changing the color.
How to Change the Color of Hydrangea Flowers
Knowing all of the above, increasing acidity (for blue) or alkalinity (for pink) is quite simple:
From Pink to Blue
To increase acidity (for dark blue flowers): apply a solution of 7 g of aluminum sulfate per 4 liters of water three times a year. (Aluminum sulfate is a colorless salt obtained by the action of sulfuric acid on hydrated aluminum oxide. Can be bought in any garden supply store). Pour the solution into the ground after the plant wakes up to growth in the spring, and repeat twice at intervals of 3-4 weeks. Once a year, in the spring, apply NPK 25-5-30 fertilizer according to the manufacturer’s instructions.
From Blue to Pink
To increase alkalinity (to change blue flowers to pink): in spring or autumn, scatter ground limestone (dolomitic lime) at a ratio of 2 kg per 30 square meters and water well. (Excessive alkalinity will cause chlorosis or yellowing of the leaves.) In spring or autumn, apply NPK 25-10-10 fertilizer according to the manufacturer’s instructions.
Other Factors
Hydrangea flowers will naturally wither and dry out in the fall, turning pink-green or brown. This is simply an aging process that cannot be reversed.
Hard water (water with a high mineral content) can also affect the color of the flowers, making blue flowers more pink, so water hydrangeas with rainwater if possible.