  We study the non-minimal supersymmetric heterotically deformed
$\mathcal{N}=(0,2)$ sigma model with the Grassmannian target space
$\mathcal{G}_{M,N}$. To develop the appropriate superfield formalism, we begin
with a simplified model with flat target space, find its beta function up to
two loops, and prove a non-renormalization theorem. Then we generalize the
results to the full model with the Grassmannian target space. Using the
geometric formulation, we calculate the beta functions and discuss the 't Hooft
and Veneziano limits.
