Grass-legume mixtures may increase dry matter (DM) yield and forage N concentration due to biological N₂ fixation. A study was conducted to evaluate yield and botanical composition in different cool season grass-legume mixtures in Gainesville, FL from 4 February to 14 May 2014 (4 harvests). Treatments were allocated in a split-plot arrangement in a completely randomized block design with 4 replicates. Main plots were formed by annual ryegrass (Lolium multiflorum Lam.) or a rye (Secale cereal L.)-annual ryegrass mixture. The subplot was the combination of cool-season legumes or presence/absence of N fertilizer in grass monocultures, as follows: (1) hairy vetch (Vicia villosa ssp.), (2) crimson clover (Trifolium incarnatum L.), (3) red clover (Trifolium pratense L.), (4) ball clover (Trifolium nigrescens Viv.), (5) hairy vetch-red clover-ball clover, (6) crimson clover-red clover-ball clover, (7) N-fertilized grass (50 kg N·ha⁻¹·cut⁻¹), and (8) unfertilized grass. Total DM yield was greater for N-fertilized grass in the 2nd and 3rd harvests (660 and 1360 kg DM·ha⁻¹). Mixtures containing subplot-Treatments 3 and 6 increased total DM yield in the 4th harvest (1250 and 1280 kg DM·ha⁻¹, respectively) and did not differ from N-fertilized grass in this harvest. Legume DM yields were minimal in Harvests 1 and 2. In the 3rd and 4th harvests, the crimson clover-red clover-ball clover mixture had the greatest legume DM yield (330 and 730 kg DM·ha⁻¹), followed by crimson clover (320 kg DM·ha⁻¹) in the 3rd harvest, and by red clover (660 kg DM·ha⁻¹) in the 4th harvest, whereas hairy vetch presented the lowest productivity in both harvests (33 and 31 kg DM·ha⁻¹). Dry matter yield of annual ryegrass and rye-annual ryegrass did not differ among harvests. Grass DM yield was greater for N-fertilized grass in the 2nd and subsequent harvests (660, 1360, and 1220 kg DM·ha⁻¹). Red clover and the crimson clover-red clover-ball clover mixture were not different in DM yield than N-fertilized grass in the last harvest, while the other mixtures did not differ from the unfertilized grass.