We combine photometric and spectroscopic data on twelve modes excited in FG Vir to determine their spherical harmonic degrees l, and to obtain constraints on the star model. The effective temperature consistent with the mean colours and the pulsation data is about 7200 K. In six cases, the l identification is unique with above 80% probability. Two modes are identified as radial. Simultaneously with l, we determine a complex parameter f which probes subphotospheric stellar layers. Comparing its values with those derived from models assuming different treatment of convection, we find evidence that convective transport in the envelope of this star is ineffcient.