Making my hydrangea blue

I am growing Hydrangea serrata Blue Bird in a pot, it is growing in ericaceous compost but the flowers are coming out pink? so I am going to use aluminium sulphate on it, how safe is this stuff? I have read that it can sometimes burn the roots, any advice muchly appreciated.

Val

 

Hiya
By using rusty nails or sulphate of iron the hydrangea will turn more blue .. Probably the ericaceous compost has a balanced ph level
Rusty nails around the plant, would work ...watering the plant with a scoop of sulphate of iron would also work ... Sulphate of iron is also a great moss eradicator for your lawn when added to sand etc
Or you can buy hydrangea colorant from your local garden centre

 

Thanks Doug, well you obviously haven't heard anything detrimental about doing this, I am going to use the Vitax colourant as pictured and apparently this contains aluminium sulphate.
I seem to be a bit short of rusty nails!!

 

I think you really should have started adding it a bit earlier in the growing season.

 

I would have but I didn't know the flowers were going to be pink!!! they are supposed to be blue!!

Val

 

Aluminium sulphate will be a effective than an Iron based material, although chucking some rusty iron in there will help (and will carry on working for some years to come of course ...)

I've not read that - perhaps its the acidifying effect?

 

Ericaceous compost is, I believe, only around the pH 6.5 mark. Strictly speaking, 7 is neutral, but in horticultural science terms (and I'm quoting theory now), 6.8 is considered neutral, so ericaceous compost is not really very acidic at all.

I was told that Flowers of Sulphur is what you need to significantly lower pH. If rusty nails was enough to make a big difference, then every patch of soil I've ever dug should be acidic.

 

Yup, but for Hydrangeas turning blue its not just the pH that's the issue, but also the presence of Aluminium (and maybe other metals, but Aluminium has been shown to be the most effective and is what is used commercially when "forcing" Blue Hydrangeas). Its worth watching the pH of the irrigation water though - particularly in hard water areas - rainwater would be better, and avoid Phosphate in the fertiliser (the middle value of the N-P-K should be significantly lower than the N or K, and for flowering then K should be higher than N - double would be good, so for example an N-P-K ratio of around 10 : near-zero : 20).

Because Aluminium Sulphate (rather than other forms of Aluminium) contains Sulphur that will help to lower the pH.

I think this may only be a problem if applied to roots that are dry, water the plants (plain water) first so that aluminium sulphate solution is not applied to plants that are dry.

 

Well I bought it from Crocus and they are usually very dependable with their plants.

Val

 

Even if you are not sure its worth leaving it a couple of years, their behaviour is more "like type" when they have matured a bit.

 

Remember years ago taking cuttings from what was a pink Hydrangea from a friend.

It then turned blue after I added some Aluminum sulphate.

I think Hydrangeas are very variable when given different growing conditions, and watering with tap water will probably affect the ph of erecacious compost long term.