Technical Abstract: Crosses between Medicago sativa subsp. sativa and subsp. falcata produce progeny exhibiting heterosis for biomass yield. The purpose of this study was to determine which subsp. falcata germplasm produced the best hybrids in testcrosses with elite subsp. sativa material in order to guide future breeding efforts. Over 100 falcata genotypes from 40 populations were test crossed to four elite sativa populations. Testcross progeny and parental clones were grown for two years in two locations and harvested three times per year to determine biomass yield. A broad range of testcross performance was observed, with mean heterosis values approximately zero. The highest yielding sativa-falcata hybrids were derived from European falcata germplasm. North American semi-improved falcata germplasm performed well in hybrid testcrosses. Pre-selection of parental falcata genotypes for autumn growth was associated with higher yielding testcross progeny. Positive heterosis was seen during the first harvest, but negative heterosis was often observed during second and, to a smaller extent, third harvests. Superior sativa-falcata hybrids were observed that showed good biomass yield and heterosis during all three harvests. Parental yield was least predictive of hybrid progeny yield during first harvest (h2 = 0.12). Heritability increased during second and third harvest to 0.31 and 0.33, respectively. Expected genetic gain per selection cycle is greater using progeny testing compared to simple recurrent phenotypic selection.