This document specifies general rules for the aerobic preparation of the initial suspension and of dilutions for microbiological examinations of microbial plant biostimulants. This horizontal method might not be applicable in very detail for certain products. In this case, different methods which are specific to these products can be used if necessary, for justified technical reasons. This document is applicable to the blends of fertilizing products where a blend is a mix of at least two of the following component EU fertilizing products categories: Fertilizers, Liming Materials, Soil Improvers, Growing Media, Plant Biostimulant and where the following category Plant Biostimulants is the highest % in the blend by mass or volume, or in the case of liquid form by dry mass. If Plant Biostimulants is not the highest % in the blend, the European Standard for the highest % of the blend applies. In case a blend of fertilizing products is composed of components in equal quantity or in case the component EU fertilising products used for the blend have identical formulations, the user decides which standard to apply.