There is currently no agreed-upon regulatory framework or legal definition for biostimulants in the United States.
In the 2018 Farm Bill, the US Department of Agriculture (USDA) uses the following definition of plant biostimulants:
"A substance or microorganism that, when applied to seeds, plants or the rhizosphere, stimulates natural processes to enhance or benefit nutrient uptake, nutrient efficiency, tolerance to abiotic stress, or crop quality and yield."
In May 2025, the Plant Biostimulant Act was reintroduced to the House and Senate with the goal of creating a uniform federal definition for plant biostimulants, establishing a consistent regulatory pathway to market, and promoting additional research into the benefits of biostimulant products on soil health and crop production.