Every year, a large amount of waste is generated throughout the food chain; about 13% of it comes from large retailers, originating from products that are not sold and are thrown away. In recent years, research has focused on the valorisation of food waste by transforming it into new products, but there is a lack of research into these products' use as biostimulants. The use of biostimulants from food waste would be a viable alternative to synthetic fertilisers, making agriculture less impactful. The aim of this study was to evaluate the use of fermented food waste as a biostimulant using a multidisciplinary approach. The fermentation process was studied and optimised with an experimental design (DoE). Lettuce was fermented with Lactiplantibacillus plantarum and tested in a greenhouse with strawberry plants at different concentrations. A morpho-physiological characterisation of the plants during vegetative development and harvest was performed, revealing that the application of the biostimulant increased the number of fruits and the chlorophyll content. The soil microbial community was studied with Biolog EcoPlate to understand changes in relation to treatment. Using this system, changes in the metabolic activity of the microbial soil community in relation to the phase of the plant cycle were highlighted.