This paper presents the results of the preliminary experiments conducted on fly ash and bottom ash samples that were collected from a fluidised-bed boiler after biomass combustion. The purpose of the research was to determine potential possibilities of the introduction of such types of waste to soil, in accordance with the ecological engineering assumptions. The following physical and chemical properties of the analysed waste were determined: particle size distribution, pH, chemical composition, and leaching. The chemical properties of the tested power-generation waste were essentially different, depending on the time of waste sample collection from the installation, despite the fact that other identical sampling conditions were observed: the same installation, the same combustion process, and the same type of fuel. To determine the eco-toxicity of the tested waste samples, the vegetation experiments were conducted that allowed to evaluate the influence of the tested waste samples on selected test plant species. The tests concerned for example the influence of fly ash and bottom ash on such physiological processes as seed germination and plant growth (the growth of both roots and shoots). The experiments indicated certain options of the introduction of the tested waste into soil. However, due to a considerable changeability of the waste composition and structure that presented a risk of the introduction of undesired pollutants into soil, including heavy metals, such use would be possible upon previous regular evaluation of the waste’s physical, chemical, and eco-toxic properties.