Keeping Hydrangeas Pink When They Bloom

Q: We have pink hydrangeas that haven’t bloomed yet. When they do bloom we want them to stay pink. I have been advised to keep the soil alkaline.

A: If you want to do it right, start by having a soil test done ( on the area where your hydrangeas are planted. You are shooting for a pH 6.0 to 6.2. At this pH, aluminum is not available to the plant. Aluminum is what enables blue flowers. If you get above 6.4 the hydrangea might have an iron deficiency. A soil pH below 7.0 is not technically alkaline soil but this is still the recommended pH for pink flowers. Your soil test report will give you a recommendation of how much lime to apply for raising the pH to 6.0. You can apply a little bit more than the recommendation to bump it up another 0.10 or so. If the recommendation specifies 40 pounds per thousand square feet, you can split it into 4 applications per year of 10 pounds per thousand square feet. (or maybe 12 pounds each time). Lime’s action in the soil gradually declines. After one year of liming, do a second soil test to see what effect the lime has had. It is probable you’ll have to apply lime every year to keep the pH in the range of 6.0 to 6.2.

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