Sequestrene iron tonic applied in spring once a year will do the same job, Avkg47, if you find aluminium sulphate difficult to get.

I think you advised me about a month ago to dose my large, ailing hydrangea with sequestrene rather than try to pot it up, Bamboo, and I did, albeit a rather late in the season. I don't know whether that is what has brought about the glorious, deep red the leaves have turned - it's never done that before, and my other, untreated hydrangeas are still defiantly deep green! Nice side-effect. I'm interested to see what colour the flower bracts are next year.

Probably is a side effect, Gattina - it's always best applied in Spring, then it lasts a whole season, but no harm will result. Pity you didn't post a pic, unusual to see red leaves on a hydrangea, must have been startling, lol!

I'm daft enough to not realise that this was something quite unusual!

I have seen a slight red flush or freckling on hydrangea leaves in autumn before though.

Hello, and I have seen same red flush on hydrangeas. The aluminium sulphate works quite differently from the sequestered iron. Both lower the soil ph, creating an acid base, but sequestered iron has more impact on the leaves to stop yellowing, and aluminium sulphate keeps blue hydrangea flowers blue, affecting the flower more rather than the plant and leaf. They are all interconnected at the end of the day, but I would always use A.S. to keep blue flowers blue. Most garden centres now stock A.S. and I have no trouble getting it.

Sequestrene keeps the flowers blue too, Avkg47, but if you can get AS easily, no problem anyway.