  Ongoing and future redshift surveys have the capability to measure the growth
rate of large scale structure at the percent level over a broad range of
redshifts, tightly constraining cosmological parameters. Beyond general
relativity, however, the growth rate in the linear density perturbation regime
can be not only redshift dependent but scale dependent, revealing important
clues to modified gravity. We demonstrate that a fully model independent
approach of binning the gravitational strength $G_{\rm eff}(k,z)$ matches
scalar-tensor results for the growth rate $f\sigma_8(k,z)$ to $0.02\%$-$0.27\%$
rms accuracy. For data of the quality of the Dark Energy Spectroscopic
Instrument (DESI) we find the bin values can be constrained to 1.4\%-28\%. We
also explore the general scalar-tensor form, constraining the amplitude and
past and future scalaron mass/shape parameters. Perhaps most interesting is the
strong complementarity of low redshift peculiar velocity data with DESI-like
redshift space distortion measurements, enabling improvements up to a factor
6-7 on 2D joint confidence contour areas. Finally, we quantify some issues with
gravity parametrizations that do not include all the key physics.
