The effect of the extract of Laminaria digitata (Huds.) Lamouroux (industrial waste, TU 10.39.30-025-41669896-2019) collected in the White Sea near the Solovetsky Archipelago on the productivity and nutritional value of rapini Brassica rapa L. subsp. sylvestris L. Janch. var. esculenta Hort. microgreens was studied under controlled environmental conditions. The experiment allowed us to identify the optimal concentration of the extract (10 ml/l) to be used as a nutrient solution for irrigation in order to augment the yield (providing plants with the necessary macro- and micronutrients) and the nutritional value of rapini microgreens, which are recommended as a functional health food. The use of higher concentrations of the extract solution (50 ml/l) resulted in a decreased yield. The results also indicate that the studied kelp extract can improve plant resistance to abiotic environmental factors, particularly low temperatures. Taken together, these finding suggest that according to the EU 2019/1009 regulation the Laminaria extract TU 10.39.30-025-41669896-2019 can be classified as a non-microbial plant biostimulant.