Mature fine tailings (MFT) are a by-product of oil sands mining that must be reclaimed through capping or use as a reclamation substrate. Some chemical and physical properties of MFT make it inhospitable for plant growth, such as high concentrations of sodium, sulfate, chloride, and hydrocarbons. A greenhouse study assessed whether substrates of various mixes of dry MFT, overburden sand, and peat mineral soil mix (PMM) and caps of forest floor organic material (LFH) and PMM would support the emergence and growth of three native grass species commonly used in land reclamation. Select vegetation properties were monitored for 16 wk in the greenhouse; select chemical and physical substrate properties were determined in the laboratory. Elymus trachycaulus was more tolerant of dry MFT than Agrostis scabra and Festuca saximontana. Mean aboveground and belowground biomass were more than twice as high on substrates with <60% MFT than on 100% MFT. Aboveground biomass was two to four times greater with capping than without and 30% greater on LFH than PMM caps. Cover and density followed similar trends. Belowground biomass on capped substrates was at least double that on uncapped substrates. Aboveground biomass was almost doubled with the use of fertilizer. High concentrations of hydrocarbons and exchangeable ions were associated with reduced plant growth and health. Results from this study show that capping, amendments, and fertilizer may improve the reclamation potential of dry MFT.