Answer: As with most varieties of Hydrangea macrophylla, the coloring in this variety (also called Monred) will respond somewhat to soil pH and other conditions. It is somewhat common to note color changes the year after planting as the roots expand beyond the original root ball. A more neutral or alkaline soil will bring out the most red coloring, while a more acid soil will bring out a bluer coloring. I would suggest you run some basic soil tests and then work to gradually acidify the soil. Your local county extension should be able to help you with the tests and with determining how to change the soil pH according to the results. You might also consider using an acidic mulch such as pine needles or pine bark, and certainly avoid applying lime near the plant. In some cases, too, planting a hydrangea near a concrete walk or foundation can be sufficient exposure to lime to affect the color. If this is a possibility, you might want to relocate the plant. Finally, weather conditions can also have an effect on the coloring, with high summer temperatures usually reducing the intensity of the redder hydrangeas. Unfortunately, there isn't much we can do on that score.
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