Current trends in agricultural intensification lead to degraded grasslands, requiring their restoration through native species reintroduction. Various techniques are available for harvesting seeds from donor sites. However, little is known about their performance in South American C3/C4 mixed grasslands, where studies are scarce. Their particular species composition and phenology, with different flowering periods, require specific harvest strategies. We evaluated mechanical seed harvest in a northern Uruguay grassland, part of Río de la Plata grasslands. Performance of two mechanical harvest methods (seed‐stripper and dry hay) was compared in two harvest seasons (late‐spring and mid‐summer). The evaluation considered the quantity and identity of harvested seeds, and their germination in a greenhouse. Hand collections were made to assess standing seed yield. For each seed mixture, efficiency of mechanical harvests (number of seeds and seedlings compared to hand collection), proportion of germinated seeds, species transfer relative to donor site, and composition were calculated. Results revealed trade‐offs between harvests: seed‐stripper in late‐spring presented low seed collection efficiency (2% for seeds, 5% for seedlings) and species richness (43% transfer), but high seed germination (64%), showing selectivity toward winter species; seed‐stripper in mid‐summer and dry hay in both seasons showed high seed collection efficiency (42–154% for seeds, 26–50% for seedlings) and species richness (65–80% transfer), resembling donor site, albeit lower seed germination (9–20%). Seed‐stripper performance varied between seasons, while dry hay remained consistently effective. These results are pioneering for grassland restoration in Uruguay, encouraging future studies to focus on establishment in the field.
