The heterogeneous crystallization of colloidal suspensions of Yukawa particles on a wall was observed by Bragg microscopy. The growth velocity ν110 of the fluid-crystal interface can be very well described by a Wilson-Frenkel growth law, while the limiting velocity is found to be lower than in previous investigations. Twinned bcc domains in lateral direction (parallel to the wall) and their ripening behavior are for the first time investigated systematically. A strong anisotropic growth behavior is found: in the direction of the shear flow, which shear melts the suspension prior to the crystallization process, the extension of the domains is much larger than perpendicular to that. The increase in domain size for short and intermediate times is found to follow a Lifshitz-Allen-Cahn ripening law, while unexpectedly for long times the ripening halts and the size of the domains remains constant.