This article presents the results of laboratory tests of the use of organic additives, i.e. lignite and sewage sludge to the mineral volcanic soil substrate and their effect on the biomass production of red fescue (Festuca rubra L. 'Dipper'). In the pots lined with geotextile fabric and filled with volcanic mineral substrate soil with the addition (by volume) of 0%, 10%, 20% and 30% lignite or sewage sludge (SS), grass was sown and regularly watered with distilled water every 10 days. The green matter and the dry matter of the yield was determined. The analysis of physicochemical properties of samples of mineral substrate, lignite and sewage sludge was carried out. On average, the dry matter of red fescue (Festuca rubra L. 'Dipper') harvested from the control substrate was 14.205 g/m2. In the variation with the addition of 10%, 20% and 30% sewage sludge, the dry matter of red fescue (Festuca rubra L. 'Dipper') was 27.636 g/m2, 23.299 g/m2, and 9.873 g/m2, respectively. The dry matter of red fescue (Festuca rubra L. 'Dipper') harvested from the substrate with 10%, 20% and 30% lignite was 16.609 g/m2, 13.149 g/m2, and 14.348 g/m2, respectively. The enrichment of the volcanic mineral substrate for green roofs with a 10% and 20% addition of sewage sludge contributed to an increase in the biomass yield of red fescue (Festuca rubra L. 'Dipper') by 94.6% and 64.0% of dry matter, respectively. The addition of lignite to the volcanic mineral substrate for green roofs contributed to a decrease in the yield of red fescue (Festuca rubra L. 'Dipper'), where, as the dose of lignite increased, the yield decreased relative to the control (by -1.5% (10%L), -20.0% (20%L), -24.2% (30%L)), most likely due to the unfavourable ratio of C:N recorded in the applied lignite (102.1:1).