if it is a relly big plant then the pot it has to go in will have to be very big. and then there is no guarentee it will survive the move. I'd do it in spring then prune down to the penultimate pair of buds. it wont flower that year but should the following year.

why not inprove the soil around the plant and give it the sequestrine into the soil. Water when dry etc. I have an old one in chalky soil and it is quite happy with a sequestrine feed once a year. the sun doesnt seem to bother it.

I'd agree with Seaburngirl - if that's an old hydrangea, you won't get it out of the soil intact anyway, their roots go down a pretty long way, and you'd need a massive container for it even if you did. Improve the soil as suggested, but also by applying a layer of organic material to the soil around the base (well rotted animal manure or good garden compost) now, together with the Sequestrene. Then next Spring when growth begins, apply a good feed such as Osmocote or Vitax Q4, keep it well watered during dry spells.

I find water-retaining gel crystals are just great for helping plants in dry soils. You could ream out a few holes around the bush (as deep as you can get) with a cane or sink a crowbar here and there round it. Then dribble in a little of the crystals in each hole - but remember that it swells massively when wet and looks weird when it erupts out of the hole if you've put too much in.

Just adding some crystals here and there under the surface should not disturb the roots too much.

Thank you so much, everyone. It looks to be on it's last legs at the moment, so anything that helps it would be a plus. I have just put all those products on my "What to bring back from the UK" shopping list. In the meantime I shall go and water it copiously once the sun has moved off it and add "Concimo acidofilo" to the wateringcan to see if that helps (liquid rhododendron feed). I assumed that so much of the product would be wasted by sinking in to the surrounding earth that the poor thing would be making frantic sucking noises in an attempt to take up enough to make a difference. I am very interested, Seaburngirl, to learn that a single dose every year is sufficient. Thank you again

I think initially I did a feed spring and autumn for the first couple of years until it looked happy. dont overdose it as that is a waste of money and may cause other problems.
You could also dig in ericaceous compost around it but that will only really help with water retention rather than a big change in the soil pH.

You could also rejuvenate it by cutting out one third of the old wood each year for the next three years

I've got no sequestrine left, but I've just given my poor old hydrangea a long cool feed of dilute rhododendron food, straight into the soil, and am about to use the same solution as a foliar feed once the sun has gone off the leaves. I shall be digging out the compost heap tomorrow, so I shall mulch it, too. It'll think it's its birthday after so much neglect. Will late October be too late for applying the sequestrine?

No, not for sequestrene - but its probably a bit late to be applying feed...

Ah, Bamboo, We still have a couple of months here before the growing season stops, and I'd like to try giving it a little boost before the leaves go. It really is sick, so anything is worth a try.......