This bill, titled the Plant Biostimulant Act of 2025, aims to amend the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) to provide a clear and consistent definition for plant biostimulants. It explicitly excludes plant biostimulants from the definitions of "plant regulator" and "pesticide" under FIFRA, clarifying their regulatory status. The bill defines a plant biostimulant as a substance or microorganism that, when applied, supports a plant's natural processes independently of its nutrient content, thereby improving nutrient availability, stress tolerance, and overall growth or yield. The legislation further defines "nutritional chemicals" and "vitamin hormone products" to differentiate them from other regulated substances. Following enactment, the Administrator of the Environmental Protection Agency is mandated to revise existing regulations within 120 days to incorporate these new definitions and exclusions. Additionally, the bill directs the Secretary of Agriculture to conduct a comprehensive study on plant biostimulant practices that enhance soil health, increase organic matter, reduce nutrient runoff, and support carbon sequestration and agricultural sustainability. The findings of this study must be publicly reported to Congress within two years of funding.