Studies on histone lysine methylation in Arabidopsis thaliana and rice ( Oryza sativa) have notably progressed in recent years. Despite these advances in knowledge, the function of histone lysine methylation in maize ( Zea mays L .) remains poorly characterized. To better understand the function of histone lysine methylation in maize, SDG102, a maize H3 lysine 36 (H3K36) methylation gene, was chosen to study functional characterization using overexpressed and knockout transgenic plants. SDG102-deficiency in maize caused multiple phenotypes, including yellow leaves in seedling, late-flowering, and increased adult plant height, while overexpression of SDG102 led to reduced adult plant height. The key flowering genes, ZCN8/ZCN7 and MADS4/MADA67, were downregulated in SDG102-deficient plants. Chromatin immunoprecipitation (ChIP) experiments showed that H3 lysine 36 trimethylation (H3K36me3) levels were reduced at these loci. Perturbation of SDG102 expression caused misexpression of multiple genes. Interestingly, overexpression or knockout of SDG102 also led to genome-wide decreases or increases in H3K36me3 levels respectively. Together, our results suggest that SDG102 is a methyltransferase in maize that catalyzes trimethylation of H3K36 of many genes across the genome, which are involved in multiple biological processes including those controlling flowering time.