Whilst I cant fault phagat's instruction for Rhodo growing.....I find that
some of mine show yellowing of the leaves every couple of years and I am on
a soil with a ph of around 5.
I use a handful or two (Depending on the size if the bush) of Nitro
chalk...which is a very high nitrogen fertilizer.........
If you do try this route then on no account let it get onto the leaves, it
will burn them fast.
Apply to the ground around the bush. You could water it on to the soil. but
I would do nothing now till the spring.
I find I have to do the same with my camellias and Azaleas....

If you can test the soil to find out the ph it will help decide on how to
treat them.

--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk