This study evaluates different hydrothermal pretreatment conditions for the tomato plant. Since these plants produce abundant waste due to their lignocellulosic content, biodegradation through anaerobic digestion is difficult. Hydrothermal pretreatment of the tomato plant was carried out at different times (0, 10, 15, 20, 30, and 60 min), with pressure and temperature conditions maintained at 394 K and 202,650 total Pa. In addition, acid and base were added to determine if they favored the hydrolysis of the lignocellulosic material. After determining the most appropriate pretreatment time for the different options (with or without chemical reagent), aerobic biodegradability was evaluated, as well as the structural changes caused by the pretreatment. From this stage of pretreatment evaluation, it was concluded that the conditions of greatest interest were 15 min (t15) hydrothermal pretreatment without the addition of chemical reagents (TPWH (t15)). The anaerobic digestion process was subsequently evaluated by comparing TPWH (t15) with the untreated tomato plant, obtaining a mean value of 0.125 ± 0.006 and 0.097 ± 0.010 m3STP CH4/kg TVS (total volatile solids) (STP standard temperature and pressure conditions, 273 K and 101,325 Pa), respectively, once the methane production is stabilized.