The biomass of grass-based Pennisetum hybrid commonly use for a biogas production via anaerobic digestion. However, it is necessary to determine a method to optimize the plant harvest time for high biogas production. Moreover, ensiling of biomass in the presence of diverse microbes may offer a solution to improve biogas production. In this study, whole plant of Pennisetum biomass (including stems and leaves) was collected at different harvesting time (plant heights of 70, 100, 150 cm), and then comparatively assessed for further ensiling and biogas production. Compared to leaves, stems exhibited a significant linear relationship (R-2 = 0.99) with whole plants in terms of ensiling quality (i.e. pH and NH3-N). Microbial analysis further revealed that Lactobacillus was the dominant bacterial genus during ensiling of stems and whole plants, with the highest relative abundance of 50.08% obtained at the height of 100 cm. Ensiling of biomass at a height of 100 cm achieved the best digestion performance, with the methane yields of 316 +/- 20 mL/g VS for leaves, 361 +/- 43 mL/g VS for stems, and 356 +/- 28 mL/g VS for whole plants. A harvesting time at the plant height of 100 cm was the optimal from the silage quality and anaerobic digestion performance. (C) 2019 Published by Elsevier Ltd.