"Emma" wrote in message
Hello. I'm a new gardener, and my question must be so basic that
even the basic gardening books can't seem to help me!

I bought a hydrangea last year and put it in a large pot.
This year I bought another one, but I've noticed that
the new one has deep green leaves and my old one looks
anaemic by comparison as the leaves are very pale green.

Sounds like an iron deficiency. I bought some 'Sequestrane' sachets for my
Azaleas, it took about a month to work. Quoting from the pack :-
"Iron deficiency results in pale yellow leaves, poor growth and
flowers",etc.
"One application last all season"
"Roses, Hydrangeas, Currants etc - 1 sachet in 4.5 litres of water per
plant"
Under "Pot plants - 1 sachet per 3.5 litres, apply as when watering
normally"

I suspect your earlier potted Hydrangea, has exhausted all the iron in the
soil.

Bertie