One of the questions we frequently received from viewers is - How do I turn my hydrangea macrophylla into that really, really dark blue or even purple? Alex tends to lean towards the blue varieties because that's what he remembers from childhood. Often times he finds plants come from a grower and are grown in a certain type of soil. The plant doesn't have the right pH to make them blue. So they use aluminum sulfate to manipulate the PH in the soil. They can really create a nice blue color by using that product. There are a range of blues and one can almost design the color for your hydrangea. If you want a Perry Winkle blue that is probably going to be a PH around 5 or 5.5. So, slightly acidic. If one wants a really deep intense blue, then a PH of around 4 should work, although it is quite acidic as far as plants are concerned. If you want a pink color, lime the soil. You will need to make the soil more alkaline, get the pH up to around 6 or 6.5 or so, which for many plants is a more normal growing PH. It is so much fun when you can have pink and blue flowers on the same shrub. But remember, when going through the process of trying to manipulate the colors it can often take a season or two to get them exactly right. And there could be a period in mid stride where one gets blues, purples pinks, light blues, all sorts of colors, it could be a quite interesting combination.