|Known as the “Queen of Forages,” alfalfa (Medicago sativa L.) is regarded for its high protein content and palatability, making it the preferred feedstuff for high-producing dairy cows. The introduction in (2005) of transgenic, reduced-lignin alfalfa as feed to dairy cows has been found to increase milk, a result of reduced lignin and increased digestibility. Simultaneously, the use of plant growth regulators and biostimulants in alfalfa production has become a topic of interest. However, there has been very limited research conducted on the yield and quality effects of plant growth regulators and biostimulants on reduced-lignin alfalfa. The objective of this experiment was to determine effects of application of indolebutyric acid (IBA), gibberellic acid (GA), kinetin, or seaweed extracts, with and without sulfur and boron, on regrowth and quality of established reduced-lignin alfalfa. Fifteen treatments with five replications and a minimum of 2-cuttings per field were applied, harvested, and analyzed for yield and quality across three fields of reduced-lignin alfalfa in Wisconsin, Illinois, and Missouri. Quality measurements included crude protein (CP), acid detergent fiber (ADF), acid detergent lignin (ADL), neutral detergent fiber (NDF), neutral detergent fiber digestibility (NDFD), relative feed quality (RFQ), and total digestible nutrients (TDN). None of the applied plant growth regulators or biostimulants consistently increased or decreased yield or quality of alfalfa with the reduced lignin trait. Overall, there were no effects of applied growth regulators on transgenic alfalfa yield or quality. At one location, the addition of sulfur and boron sometimes increased alfalfa yield, but never quality.