Garden Pests and Diseases: Anyone knows what could be wrong with my Fatsia Japonica?, 0 by bonitin

bonitin wrote:
One of my two big Fatsia Japonicas started to look unhappy since last year. It's planted near the foot of a huge old wall and grew very well during 5 years. Its leaves became only a fraction in size from what they were before. They look yellowish with only healthy green around the veins.
I guess it's lacking a particular nutrient but all the surrounding plants look healthy so I'm puzzled. Last year I've given it some slow-release general organic (dry cow-dung) fertilizer, but it didn't give any result.

Any advise will be very much appreciated as I don't want to loose it..