Two grass species, Festuca rubra (sown) and Calamagrostis epigejos (naturally recolonised), were studied at two fly ash deposit lagoons, weathered 5 (L1) and 13 years (L2). Both species were assessed in terms of their invasive ability, photosynthetic efficiency, trace elements accumulation, and damage symptoms, while the characteristics of the habitat were assessed in terms of trace element content, and the pH and EC of the ash. In the ash weathered for 5 and 13 years, B and Mn concentrations fell within the normal range for soils, while there was an As, Mo and Cu excess, and Se and Zn deficit. There was no difference in the photosynthetic efficiency (ns) of the C. epigejos populations at the different-aged ash lagoons, but differences were found between the populations of F. rubra (P<0.001). F. rubra displayed damage symptoms, in the form of leaf tip chlorosis and necrosis, and wilting seedlings--a result of B accumulation in toxic concentrations and a Cu and Mn deficit. After 13 years the sown F. rubra remained over 9.5% of the ash lagoon's area (L2), while over the same period the naturally recolonised C. epigejos had overgrown 87.5% of the area. The greater colonisation and survival potential of C. epigejos is a result of multiple tolerance to the conditions at ash deposits and of the competitive ability of this species to dominate the colonised habitat. Therefore, characteristics of naturally colonised species can be used for modelling future actions of biological restoration of fly ash deposits aimed at binding the ash with minimal investment (the short-term aim), and for providing conditions for revegetation, and shortening the successive phases in the revegetation of ash deposits after the closure of thermal plants (the long-term aim).