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Why does different soil pH affect hydrangea flower color?

Soil pH is the major determinant of hydrangea flower color. The soil pH, refers to the measure of acidity or alkalinity of the soil whose scale ranges from 0 to 14. Seven represents the neutral value. Alkalinity is indicated by pH levels that are higher than 7 up to 14, while the acidity is represented by pH values below 7. The average garden soil's pH ranges from 5.5 to 6.5, thus it is slightly acidic. Nonetheless, it is common for normal garden soil pH to range from 4.5 to 7.5. Pink hydrangeas are grown in slightly acid or neutral soils while blue hydrangeas need highly acid soils.

The 'Nikko blue' variety of hydrangea produces pink flowers if planted in neutral soils. A pH of 4.5 causes the color to be deep, vivid blue. However, as the pH scale goes upward to approach neutral, the color starts to change from blue to purple, purple to mauve, then mauve to pink.

Before attempting to manipulate the color of hydrangea flower, the soil pH has to be determined. Once the pH test has been conducted and the pH determined, you can be able to tell the alkalinity or acidity of your soil. If you grow hydrangeas in two kinds of soils, you may opt to check both soil types for the pH levels.

Blue hydrangea flowers turn to lavender, then pink as you raise the pH or soil alkalinity. Addition of lime to the soil can do this. The aluminum element causes the blue hydrangea color. However, aluminum becomes less available to the plant as the soil pH approaches the neutral level. Addition of lime to the soil makes the soil more alkaline, turning the color of the hydrangea flowers from blue to varying levels of pink.

Addition of lime can be done in four-ounce increments until the desired pink color is reached. Alternatively, you may decide to raise the soil pH to 6.5. Depending on the soil's initial acidity and texture, the process can be long; it can take up to two growing seasons if the soil is extremely acid. Addition of phosphorus or nitrogen also helps in preventing the absorption of aluminum. It also leads to a good, clear pink hydrangea color.

On the other hand, if you want to turn pink hydrangea flowers into purple or blue, you should lower the soil pH to raise the acidity of the soil. Addition of aluminum sulfate to the soil around the base of the plants can help do this. Nonetheless, addition of aluminum sulfate should not be overdone. Note that the addition of phosphorus or nitrogen promotes pink colors. Moreover, you should add single-element fertilizers like potash or muriate.

Hydrangea flower color changes do not occur overnight and at times, it is not predictable. The soil and genetics of plants both play a huge role in manipulating flower color. Additionally, fertilizers with different elements play a role in raising or lowering soil pH, thus leading to different resultant colors.

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