Microwave Assisted Extraction (MAE) was used to obtain aqueous extracts of Baltic seaweeds. Three different temperatures: 25, 40, 60°C were examined. Algal extracts were characterized in terms of polyphenols, micro- and macroelements, lipids content and antibacterial properties. This is the first study that examines the effect of algal extract obtained by MAE in plant cultivation. The utilitarian properties were checked in the germination tests on Lepidium sativum for three dilutions of extract (0.5, 2.5 and 10%). Results showed that the content of polyphenols in extracts decreased with temperature, whereas the content of micro- and macroalements increased with temperature. The aqueous extracts did not contain fatty acids and did not show inhibitory effect on Escherichia coli and Staphylococcus aureus. Germination tests showed that plants in the experimental groups with an optimal concentration of extract had a higher height, weight, chlorophyll and micro- and macroelement content than plants in the control group. The algal extracts did not significantly influence the morphology of plants as shown in SEM pictures. Results show that algal extracts obtained by MAE have the highest potential applied in agriculture as biostimulants.