Fuchsia requires low to medium fertility levels between 100 and 200 ppm N. Optimal substrate pH values for fuchsia range from 5.5 to 6.2. Fuchsias can develop both low and high substrate pH disorders. If the substrate pH drifts lower than 5.5, iron (Fe) and manganese accumulate at toxic levels and are observed as lower leaf black spotting. Substrate pH values above 6.5 inhibit Fe availability and induce interveinal chlorosis and stunted plant growth.
Read more at e-GRO (W. Garrett Owen, Josh Henry, Brian E. Whipker)