  We present results on the semileptonic decays $B^0 \to \rho^- \ell^+
\nu_\ell$ and $B^+ \to \rho^0 \ell^+ \nu_\ell$ in a sample corresponding to
189.9/fb of Belle II data at the SuperKEKB $e^- e^+$ collider. Signal decays
are identified using full reconstruction of the recoil $B$ meson in hadronic
final states. We determine the total branching fractions via fits to the
distributions of the square of the "missing" mass in the event and the dipion
mass in the signal candidate and find ${\mathcal{B}(B^0\to\rho^-\ell^+
\nu_\ell) = (4.12 \pm 0.64(\mathrm{stat}) \pm 1.16(\mathrm{syst})) \times
10^{-4}}$ and ${\mathcal{B}({B^+\to\rho^0\ell^+\nu_\ell}) = (1.77 \pm 0.23
(\mathrm{stat}) \pm 0.36 (\mathrm{syst})) \times 10^{-4}}$ where the dominant
systematic uncertainty comes from modeling the nonresonant $B\to
(\pi\pi)\ell^+\nu_\ell$ contribution.
