Is December in PNW too early to spray chelated iron on woody shrub?

I have several acid-loving shrubs that appear to be under great stress with lots of red splotches and yellowing leaves due, I think, to some new soil I put in the beds and pots six months ago. I have amended the soil with shredded oak leaves from the recent fall and some peat moss but wonder if it is too early to spray the leaves with an iron supplement. Everything I read suggests this is done in the spring to coincide with new growth. I'm concerned that if I wait too long the plants will die, that the iron would serve as a sort of vitamin boost if I spray now... just don't want to do it too early, if that causes another kind of stress. I'm in zone 9, Victoria BC. Thanks!
(Some images of the plants are below).