Hydrangea leaves going purple and brown

Hi, I’ve signed up to this site in the hope of getting some advice. I’ve had a hydrangea in a pot for a number of years (at least 5?) and it has always been healthy and flowered nicely, even recovering when left for almost 3 weeks in the 2018 heatwave!
This year the leaves did die off a couple of months ago but then recovered and re-grew lots. They’ve now started going purple at the edge of the leaves and there are spots that have died, going brown and crisp. I’ve tried watering and leaving it a little bit and given it some basic plant food. Does any know what might be the issue and how I can help it? It had some flower buds but they seem to have gone a bit brown and it really developed either.

 

I'd guess that 5 years in the same pot is the answer.
By now, the roots are probably stressed and bound up.
You can either put it in a bigger tub, or better still find a space in open ground.

 

After 5 years, with a bigger root system, it may now need more water than you provide in the summer. If you also use rocks as mulch, that will keep things toasty at night. Terra cotta pots will also lose moisture fast compared to other materials.

If the leaf edges are turning brown and browning inwards, that means the leaves lack enough water. Water the soil when the top 10 cm feel dry to the touch. Avoid watering the leaves themselves as this can promote development of some leaf spots.