hydrangeas - Knowledgebase Question

Plymouth, Mi
Question by alesatak
November 20, 2009
I want to change the color from blue to pink. How do I change the soil and when do I change it? The plants about one year old - planted in 2008 and were deep blue - by the end of this season, they were a faded pink for the most part. would like to change to deep pink


Answer from NGA
November 20, 2009


Soil acidity or alkalinity will change the color of hydrangea blooms. You can change the color back by treating the soil. Pink and red hydrangeas often turn blue or purple in acid soils, and plants can be made red by liming the soil or applying superphosphate. For blue flowers, treat the soil with 2 Tablespoons of aluminum sulphate per plant, making 4-6 applications at 2 week intervals, starting in the early spring before the plants bloom. (Sulfur will acidify the soil. The desired pH range would be between 5.5 and 6.) For pink flowers, add lime to the soil, to raise the pH above 6.5. Test your soil to measure the pH range. In general, 4 ounces of lime around the base of your hydrangea plant can change the pH of your soil by one point.

You can add lime in four-ounce increments until you reach the color of pink you desire. You need to try and raise your pH to 6.5. Depending on your soil texture and how acid your soil was to begin with, this can be a long process, taking up to 2 growing seasons.

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