  We extend the usual notion of Petersson inner product on the space of
cuspidal Jacobi forms to include non-cuspidal forms as well. This is done by
examining carefully the relation between certain "growth-killing" invariant
differential operators on $\mathbf H_2$ and those on $\mathbf{H}_1 \times
\mathbf{C}$ (here $\mathbf H_n$ denotes the Siegel upper half space of degree
$n$). As applications, we can understand better the growth of Petersson norms
of Fourier Jacobi coefficients of Klingen Eisenstein series, which in turn has
applications to finer issues about representation numbers of quadratic forms,
and as a by-product we also show that \textit{any} Siegel modular form of
degree $2$ is determined by its `fundamental' Fourier coefficients.
