Some EU member states allow the use in agriculture of a class of substances, known as plant strengtheners, under national laws. Plant strengtheners (biostimulants) enhance the resistance of plants to harmful organisms and protect plants against non-parasitic impairments. They are “borderline” products because the boundaries between plant protection products and fertilizers are not clear and univocal. There is no European regulatory framework for these substances. This fragmented and contradictory situation can prejudice the fair productive competitiveness of agriculture systems in Europe.