Abstract Studies were conducted on the effect of additives on microbial succession and silage fermentation of two alfalfa cuttings, each harvested at three maturities, and three whole-plant corn hybrids. The alfalfas were treated with dextrose at 2% (DM basis), Biomate ® inoculant ( Lactobacillus plantarum and Pediococcus cerevisiae ), a combination of dextrose and Biomate ® , or left untreated (control). The corn hybrids were treated with 1174 ® inoculant ( L. plantarum and Enterococcus faecium ) or left untreated (control). Counts of the lactobacilli, pediococci, and leuconostocs group were higher for the alfalfa silages treated with Biomate ® than for the control silage and the silage treated with dextrose only at d 1 of the ensiling period. Addition of 1174 ® inoculant to the corn silages did not influence the counts of the group that includes lactobacilli, pediococci, and leuconostocs. The numbers of other microorganisms were not affected by additive treatment for either crop. Alfalfa silages treated with the combination had the highest lactic acid and the lowest pH, acetic acid, ethanol, and ammonia N throughout the ensiling period. The pH of fourth-cutting silages treated with dextrose was lower than that of controls, and dextrose reduced acetic acid content in the second-cutting, 90-d silages. The 1174 ® inoculant did not influence fermentation characteristics of the corn silages at any time, regardless of the hybrid.