This article is about a decoding algorithm for error-correcting subspace codes. A version of this algorithm was previously described by Rosenthal, Silberstein and Trautmann. The decoding algorithm requires the code to be defined as the intersection of the Plücker embedding of the Grassmannian and an algebraic variety. We call such codes \emph{geometric subspace codes}. Complexity is substantially improved compared to the algorithm by Rosenthal, Silberstein and Trautmann and connections to finite geometry are given. The decoding algorithm is applied to Desarguesian spread codes, which are known to be defined as the intersection of the Plücker embedding of the Grassmannian with a linear space.