This paper analyzes the effects of substrate properties and environmental conditions on spontaneous vegetation of soil and sludges from a dismantled steel plant moderately polluted by heavy metals and polycyclic aromatic hydrocarbons. Plant colonization was monitored in presence or absence of acidic peat for five years both inside the degraded brownfield site and after transferral into a nearby Oak Park environment. Overall, 57 plant species grew healthily on the substrates, with peat enhancing plant growth in the unfavorable brownfield site. Most of the species were found in the park (91%), showing plant colonization was mainly affected by the immediate environment rather than by substrate properties. Restricted metal uptake and tissue accumulation by selected plants was measured, with only Daucus carota showing a higher ability to translocate metals to shoots (shoot/root metal concentration quotient >1 with peat). Phytostabilization with native plants represents an economically more realistic and cost effective option than excavation, soil washing and sludge disposal, especially for vast industrial sites. Addition of organic matter and planting strategically-selected vegetation islands could facilitate the spontaneous recovery of such highly degraded environments.