Yellowing leaves on a Japanese Snowbell

Hello all, I just came home from an extended holiday to find my snowbell in poor condition, I am guessing it needs some fertilizer can anyone suggest the best way to deal with the yellowing leaves? The surrounding trees which includes a 2nd snowbell are all doing fine.

 

Check soil moisture.

 

My husband has it on a timer...too much? Aside from lowering the flow or letting it dry out should I fertilize? Thank you so much.