This paper investigates the spatial behavior of the solutions of the
double-diffusive Darcy plane flow in a semi-infinite channel. Using the
energy estimate method and the differential inequality technology, a
differential inequality about the solutions is derived. By solving this
differential inequality, it is proved that the solutions grow
polynomially or decay exponentially with spatial variable. In the case
of decay, we obtain the upper bound for the total energy. We also give
some remarks to generalize the results of this paper.