We investigate the star formation properties of ~800 sources detected in one of the deepest radio surveys at 1.4 GHz. Our sample spans a wide redshift range (~0.1 - 4) and about four orders of magnitude in star formation rate (SFR). It includes both star forming galaxies (SFGs) and active galactic nuclei (AGNs), further divided into radio-quiet and radio-loud objects. We compare the SFR derived from the far infrared luminosity, as traced by Herschel, with the SFR computed from their radio emission. We find that the radio power is a good SFR tracer not only for pure SFGs but also in the host galaxies of RQ AGNs, with no significant deviation with redshift or specific SFR. Moreover, we quantify the contribution of the starburst activity in the SFGs population and the occurrence of AGNs in sources with different level of star formation. Finally we discuss the possibility of using deep radio survey as a tool to study the cosmic star formation history. ; Comment: 18 pages, 14 figures, 1 table (available in its entirety as ancillary data)