We have measured the saturation temperature, Ts, for growth of ( YEu ) 3 ( FeGa ) 5 O 12 films in a PbO ‐ B 2 O 3 flux over a wide range of oxide concentrations and over the temperature range 850 – 1050°C. This temperature range is of the most practical interest in film growth by liquid phase epitaxy (LPE). We have also studied the ( YGdTm ) 3 ( FeGa ) 5 O 12 system less extensively. Ts, as expected, increases with increasing total garnet oxide concentration. It increases sixteen times more rapidly with increasing rare earth oxide concentration than with increasing iron oxide concentration. However, neither the rare earth oxide nor the iron oxide concentrations separately limit growth even for large iron oxide to rare earth oxide molar ratios, R 1 . We have found that the garnet phase exists from R 1 = 12 to at least R 1 = 66 . We shall present an empirical binary phase diagram which specifies Ts as a function of both iron and rare earth oxide molar concentrations and discuss its implications for LPE garnet film growth.