This document specifies a method for determination of the content of mercury (Hg) in plant biostimulants using (cold) vapour generation apparatus coupled to an atomic absorption spectrophotometer and a method using a direct amalgamation technique. It is applicable to aqua regia digests prepared according to EN 17701-1: 1. NOTE It is also possible to use other suitable methods for the determination of mercury described in Annex A if users prove that the method gives the same results as the methods described in this document. This document is also applicable to the blends of fertilizing products where plant biostimulants are the main part of the blend. Otherwise, the method for the main part of the blend applies.