This document specifies the method for the digestion of different plant biostimulants with aqua regia to enable a subsequent determination of arsenic (As), cadmium (Cd), copper (Cu), chromium (Cr), mercury (Hg), nickel (Ni), lead (Pb) and zinc (Zn). The method can be also applied for determination of other elements. The method is applicable for all solid and/or liquid plant biostimulants. This document is also applicable to the blends of fertilizing products where plant biostimulants are the main part of the blend. Otherwise, the Technical Specification for the main part of the blend applies. The extracts are suitable for analysis using CEN/TS 17701-2 (ICP-AES) and CEN/TS 17701-3 (Hg analysis). NOTE – Alternatively, inductively coupled plasma mass spectrometry (ICP-MS) can be used for the measurement if the user proves that the method gives the same results.