If they're in the ground, you don't have to give them anything ifyour soil is quite good, but if you want to, lightly rake a bit of Growmore or something similar around the base.

I feed my camelis and rhodoies in the ground with Miracle grow Camelia and rhodendron granule feed.

Hoof and horn is a recommended slow release nitrogen fertiliser for ericaceous plants, if you are pure organic. Also there are liquid feeds with chelated trace elements suitable for camellias, as well as the granular feed mentioned above.

I am on neutral clay and the pot grown Camellia got too big, so I risked planting out. With the same as Scotkats feed it does well with little chlorosis.....its the late frosts though..... :0 (
Still the leaves are glossy lol!