Ongoing losses to mangrove forests globally have prompted increased interest in restoration programs that seek to restore vital ecosystem functions and services. In many cases, data on local-scale environmental tolerances of mangrove species used in reforestation efforts is lacking, and failure of restoration projects has been attributed to incorrect species selection in plantations. Here, we assess the impact of soil salinity on the early establishment success of monospecific red mangrove Rhizophora mangle reforestation projects in the Saloum Delta, Senegal, a region where widespread mangrove restoration efforts are ongoing. At soil salinities >60 ppt, stomatal conductance, photosystem II operating efficiency, and growth of planted R. mangle seedlings were severely reduced. Similarly, after 1–3 years, survival of mangrove seedlings decreased in soil salinities of >60 ppt. In contrast, we recorded naturally occurring black mangrove Avicennia germinans growing in exceptionally hypersaline conditions (90 ppt), representing some of the most saline vegetated ecosystems on Earth. The findings reported herein can be used to inform species choice in reforestation projects and help improve success rates of coastal wetland restoration projects in semiarid regions.