Lactic acid bacteria (LAB) can be used as silage additives to ensure rapid and vigorous fermentation at early stages of ensiling. We predicted that the optimal LAB inoculation dosage for forage at ambient temperature (15–38°C) would be different from that at cold temperature (4°C). In this study, Lactobacillus plantarum QZ227, isolated from a wheat landrace in alpine regions of Qinghai, China, and commercial L. plantarum FG1 were used as inoculum, with sterile water as control. The effects of inoculum dosage on the fermentation quality of oat (Avena sativa L. cv. Qinghai) and wheat (Triticum aestivum L. cv. Yumai No. 1) silage at ambient temperature (15–38°C) and at 4°C were investigated in laboratory experiments. Little or no improvement in silage quality occurred upon increasing the inoculum dosage at ambient temperature. By contrast, a lower pH and NH₃-N content, and a higher LAB count and lactic acid content, were observed at 4°C. Furthermore, the growth of Escherichia coli was inhibited effectively at the lower temperature, and silage quality was positively correlated with increasing inoculum dosage (P < 0.05). These results suggest that increasing the inoculum dosage could improve the quality of silage at lower temperatures of 4°C, whereas an appropriate dosage was a key factor for silage at ambient temperature. In this study, oat forage could be used as raw materials for ensiling only at low temperature but was not suitable for ensiling at ambient temperature without wilting due to the high moisture content (86.55%). QZ227 isolated from the roots of wheat in alpine regions displayed superior antimicrobial properties against yeast at ambient temperature and E. coli at 4°C compared with commercial strain FG1. This is the first study to explore the effects of inoculum dosage on silage quality at low temperatures, and provides a basis for low-temperature silage technologies.