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The Osisko open-pit Au mine in Quebec, Canada, produces low-grade ore at 55 000 t/day and the non-acid generating wastes will eventually cover large surfaces that will need to be reclaimed. Milling wastes will be deposited as thickened tailings to minimise water consumption. Two studies were carried out, the first involving the establishment of plantations on compacted waste rock covered with overburden topsoil or subsoil at two compaction intensities and the second in a glass house to evaluate the capacity of the thickened tailings to sustain the growth of tamarack, jack pine, black spruce, basket willow, hybrid poplars and green alder. Tailings alone or mixed with amendments including overburden soils, vermicomposts from food wastes, chicken manure and peat were tested, and the use of a thin or thick layer of overburden topsoil was also investigated. The results showed that direct planting in the thickened tailings was not suitable for boreal trees, probably due to the high water retention capacity and low macroporosity of the substrate which limited O2 availability required for root respiration. An organic matter-rich amendment increased the macroporosity to levels suitable for tree growth, with peat being the most effective amendment. Composts produced appropriate porosity levels but also increased electrical conductivity to levels which limited broad-leaved species survival and conifer biomass production. No trace metal contamination of the trees occurred in the mixtures, and the presence of underlying alkaline tailings limited Mn, Zn and Al phytotoxicity of the acidic overburden topsoil layer from occurring in tree leaves. Growth was improved with a thin layer compared with a thick layer of overburden soil, although the trees showed Cu accumulation in the fine roots., The Osisko open-pit Au mine in Quebec, Canada, produces low-grade ore at 55 000 t/day and the non-acid generating wastes will eventually cover large surfaces that will need to be reclaimed. Milling wastes will be deposited as thickened tailings to minimise water consumption. Two studies were carried out, the first involving the establishment of plantations on compacted waste rock covered with overburden topsoil or subsoil at two compaction intensities and the second in a glass house to evaluate the capacity of the thickened tailings to sustain the growth of tamarack, jack pine, black spruce, basket willow, hybrid poplars and green alder. Tailings alone or mixed with amendments including overburden soils, vermicomposts from food wastes, chicken manure and peat were tested, and the use of a thin or thick layer of overburden topsoil was also investigated. The results showed that direct planting in the thickened tailings was not suitable for boreal trees, probably due to the high water retention capacity and low macroporosity of the substrate which limited O2 availability required for root respiration. An organic matter-rich amendment increased the macroporosity to levels suitable for tree growth, with peat being the most effective amendment. Composts produced appropriate porosity levels but also increased electrical conductivity to levels which limited broad-leaved species survival and conifer biomass production. No trace metal contamination of the trees occurred in the mixtures, and the presence of underlying alkaline tailings limited Mn, Zn and Al phytotoxicity of the acidic overburden topsoil layer from occurring in tree leaves. Growth was improved with a thin layer compared with a thick layer of overburden soil, although the trees showed Cu accumulation in the fine roots.