A seed treatment method, using a composition obtained extemporaneously by mixing at least one powder substance and an aqueous medium, comprising the steps consisting of: producing the mixture in an automatic and cyclic manner, in at least one first vessel (10 10′), by introducing into same first at least a portion of the aqueous medium and next the powder substance, the latter being sucked into the aqueous medium in the vessel by means of a vacuum created in the vessel, at least partially draining the content of the vessel, by means of at least one blast of compressed gas in the vessel, to a seed treatment device where the mixture is brought into contact with the seeds.
