While mixed-species cover crops are gaining worldwide popularity, their utility in the ‘plough-out’ period in tropical sugar cane systems has not been investigated. Field trials investigating weed suppression (one season only), biomass production and nitrogen accumulation of single-species and mixed-species cover crops were conducted over two seasons on a commercial sugarcane farm in the Australian tropics. Mixed-species cover crops showed strong weed suppression, and were among the top treatments for biomass production each year, but did not yield the highest biomass in either season. Sunn hemp (Crotalaria juncea cv. Global sunn) produced the most biomass in the drier-than-average 2016–2017 season (>10 t dry matter ha−1), while soybean (Glycine max cv. Leichardt) produced the most biomass (5.3 t dry matter ha−1) in the wetter-than-average 2018–2019 season, highlighting the influence of seasonal conditions on species’ biomass production. The inclusion of multiple species in a short-term cover crop in the tropics where extreme weather events can occur can thus be seen as a risk mitigation strategy given the risk of failure of any given species in a given season.