What has happened to my camelia?

I have 2 camelias, one I have had for 30 years and the other about 10 years planted in the garden (not tubs), and have always had profusion of flowers. This year it was very poor and ALL the leaves on both trees have turned yellow and are falling off, with no new foliage appearing, so it is more or less leaving them with bare branches. I did last autumn give the 2 camelias some phosphergen)This has also happened to an old rhodi (in a different part of the garden). What has gone wrong?