Or plant Hydrangea Pia. My soil is quite acid and it is pink, pink, pink.

In any event, I would not put rock under hydrangea. I attended a lecture given by Penny McHenry, founder of the hydrangea society and breeder of the Penny Mac hydrangea. She strongly advised a once-a-year topdressing of compost, which of course you can't do if you put down rocks.
Christine

Thanks Christine, Pia is nice but there are others that I want too. Actually I probably will order Pia some time. I was thinking of a simple way to raised the pH since I tend to forget to lime. I like pink hydrangeas. The rocks would be thinly placed not heaped up. We really don't have access to compost here- the best you can get is manure from a bag!

Rock - just any rock, like marble - will have no significant effect on soil pH. If you want to raise pH you will need to apply lime. There are hydrangea varieties that will bloom pink pretty much regardless of pH: 'Pia' is one already mentioned but also 'Glowing Embers', 'Masja' or 'Geoffrey Chadbund (lacecap) should produce pink flowers in even acidic soil.

And virtually any of the panicle hydrangeas - Hydrangea paniculata cultivars - will have flowers that will age to shades of pink, rose or red regardless of soil chemistry. And some, like 'Quickfire' or 'Vanilla Strawberry', will offer this color quite early in the season.

Thanks, I already many hydrangeas that need liming to stay pink, I was thinking of an easy and lazy way do it. And I also did read, somewhere online, that marble rock will raise the pH just like concrete may also do. It was a warning for something I think. It is just CaCO3 after all and quite soft too, much softer and more soluble than concrete.