Answer: Although many of the bigleafed hydrangeas will change color in response to the soil pH, some have been bred to remain a constant color, or relatively so, over a range of soil pH. You might look into some of the varieties selected for steady (or almost always) pink coloration such as "Forever Pink" or "Pink Elf" or "Pia" or "Glowing Embers" among others.
You might also simply allow room between the hydrangeas to avoid having the acidifier contacting the soil around the "pink" hydrangea's roots. You could fill the space with a garden bench, an ornament or perhaps some other type of plant that would complement the hydrangeas.
Enjoy your pink hydrangea!
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