Answer: There are different types of hydrangeas, and to some extent their size and coloring will depend on the variety you are growing. (Some are smaller than others, however, and some are always pink flowered, or have pink buds opening to white flowers for example, regardless of soil pH.)It is possible that the pine trees roots are competing with the hydrangeas and thus causing them to be small, but it is also possible that this is their normal size range and color.
The big leafed hydrangeas usually (most types) respond to an acid soil by having bluer flowers and to a neutral to alkaline soil by producing pinker flowers. Next, pine needles are in fact acid and house foundations are often alkaline due to the cement used in them, so the soil pH may be affected by both of these. To determine the pH of your soil as well as its overall fertility, you would need to run some basic soil tests. Your county extension should be able to help you with the tests and interpreting the results with an eye towards the hydrangeas. They should also be able to help you decided if it would be a good idea to move them, or not.
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