Thursday, November 23, 2017

The hydrangea blues

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 colour to be truly purple, they're a bit further along the colour 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 sulphur powder or liquid sulphur. (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 aluminium 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 colour a bit. If it's not that effective, I'll add a bit more later on.

This is the alternative "Option B" product, the aluminium sulfate "blueing" mixture. I didn't buy this and don't intend to, but lots of people prefer a quick fix to a slow fix, and so if you want to turn your pink hydrangeas blue within a few weeks, get some aluminium sulfate.

Finally, in case you're wondering, you can't change the colour of white hydrangeas. In the same soil that's turning my blue hydrangeas into a lilac haze, Pammy's white hydrangeas are looking splendidly healthy, handsome and dazzlingly white.

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.


MDN said...

It's hydrangeas time here in Argentina too! My hydrangeas are generally pink , sometimes blue I still don't understand why.. my soil must have a crazy PH: some years they are pink and some years they are blue!

Jamie said...

MDN, I agree with you – your soil must be crazy! Haven't got a clue why that would be happening ...

Apuff Wern said...

That was interesting about hydrangeas how do You rate them against chyrsantheums?

Jamie said...


I've never grown chrysanthemums and I don't think I ever will, so my opinion is probably worthless.

But if you want to grow chrysanthemum, go ahead and do it!

Best wishes


Phil in Newy said...

Hi Apuff & Jamie. Chrysanthemums are high-maintenance compared to hydrangeas. They will die back and shoot again next season and probably require staking, etc. But they are beautiful, due to the endless varieties and a glorious herb-like aroma in both leaves and flowers. I grew them commercially for a while and working in that cloud of Chrissie aroma is an experience that will be with me for life :0)

PS: This year I tried a selection of seeds from eBay with mixed germination results. But did buy a PURPLE rooted plant and it's going to be a spectacle. Starting to bud.

Used to be lots of Dutch cuttings specialists in Victoria but can't find many now, so usually buy some potted ones in flower around Mothers' Day and plant them out. Whoops, sorry, this is Jamie's blog!

Jamie said...

No worries, all good info Phil. Hijack away!