I thought as much ... the "blue" hydrangeas I planted recently are just completely normal hydrangeas which turn pink in alkaline soils, or turn blue in acid soils. Mine are a lilac colour, which isn't what I want, and so here's the story of giving my lilac hydrangeas a case of the hydrangea blues. It isn't rocket science, but it is science.
See what I mean? Those large flower petals are the originals. They're not a deep enough color to be truly purple, they're a bit further along the color wheel towards the pink end of the spectrum. And so that means my soil pH in this spot is probably somewhere about 5.5 to 6. The next lot of baby buds coming through are looking a lot bluer, though.
Normally, my garden soil is more down the acid end of the spectrum, somewhere about pH 5, and that should produce nice blue hydrangeas. However, the soil in this part of the garden is about 50 per cent homemade compost, and I guess that's why its pH is a bit higher (my guess is something closer to pH 6).
None of this is a problem, of course. In fact it's just another excuse for some good gardening fun. After much Googling and reading, I realised there are two ways you can go about turning your hydrangeas blue.
Option A is to change the soil pH itself on a semi-permanent basis, using either sulfur powder or liquid sulfur. (And it is also spelled "sulfur" on some product labels, which apparently is how the scientific community has agreed it should be spelled). This is slower acting than option B, but is a more long-lasting, possibly permanent, solution as it changes your soil's pH. It's often used by gardeners growing acid-loving plants such as azaleas, camellias and blueberries.
Option B is to apply a "hydrangea blueing" mixture (liquid or powder) which is made from aluminum sulphate. This is faster acting, but it needs to be reapplied every month or so to keep the hydrangeas nice and blue. I didn't like the sound of that, so I was "yeah, nah" to this method.
This is what our local Mitre 10 store had in stock, so I bought it and applied it to the soil around each plant, then watered it in. The pack comes with a spoon and a guide to how much to use. I've taken a cautious approach and applied half a dose to each plant, and I am sure it is already affecting the flower color a bit. If it's not that effective, I'll add a bit more later on.
Those white flowers on a backdrop of deep green leaves really do look nice. This plant is still, of course, a baby, but the plant label says once it is is mature it will be 1.2 metres (4 feet) tall and wide, which is something I am looking forward to enjoying for many years to come.
