The degradation of urban soil quality is an emerging issue caused by rapid urbanisation, poor land management practices and pollution. These factors lead to reduced soil fertility and diminished vegetation in certain areas. Biomass ash, a byproduct of the biomass combustion process, proved to be an effective soil amendment due to the high levels of major soil nutrients, most notably calcium, potassium, and phosphorus. However, managing the fine particle size of biomass ash is problematic because wind could disperse particles into the air and migrate them to unwanted places, possibly causing wastewater pollution or even respiratory health hazards. To address these challenges and produce effective urban soil fertilisation techniques, this study explores pelletisation of biomass ash with gypsum as a stabilisation technique and its application on degraded soil using various application rates ranging from 1 t/ha to 7 t/ha. A series of controlled experiments were conducted to determine the ash pellets impacts on soil pH, nutrient availability, and plant biomass growth. The findings show that pellets of biomass ash to gypsum of ratio 5:1 with 12 % water addition were the most optimal to minimise binder usage and produce pellets durable enough for transportation and field distribution. Biomass ash considerably improves soil quality by increasing nutrient content in soil with a potassium increase in soil from an initial 1.2450 ± 0.00225 % concentration up to 1.4889 ± 0.0268 % and a calcium increase from an initial 1.8016 ± 0.0213 % concentration up to 2.3438 ± 0.0230 % depending on the fertilisation rate. Research has revealed that soil fertilisation using ash pellets with a rate of 1 t/ha showed no significant increase in biomass yield; however, higher fertilisation rates can increase ryegrass biomass yield by 9–38 % with the highest increase in biomass yield with biomass ash addition of 7 t/ha. The study underlines the potential of biomass ash pellets as an environmentally sound and sustainable solution to urban soil remediation as well as the reduction of waste. © 2025 Norbertas Eigelis et al.