They like a free draining soil could it have become a bit waterlogged?
I wouldn't disturb the roots but give it a gravel mulch
that should work its way down in time,
as for a feed my garden all gets a balanced fertilizer this time of year

Thank you. It seems quite happy in its pot and flowers profusely each year - not waterlogged just a little bit anaemic looking.

I tend to use the slow release fertiliser, the little orangey yellow balls, they only release their nutrients if the temperature is right, it goes in all my baskets and grobags just in case.

Next time I go to the gc I shall get some. Many thanks.