Why does my dog sneeze near plants? Is it allergies? What can I do?

Hello and welcome to Petco Pet Education Center, formerly Petcoach. The sneezing could be caused by allergies to the plants, just like people. Removing the plants or having them up high where KoKo can't smell them is an option. If you remove the plants and KoKo is still aggressively sneezing, then he might have something stuck in his nose. In this case I would have him seen by a vet right away to check him over, as foreign objects and grass seeds in the nose can cause severe damage if not removed early. If the sneezing goes away with moving the plants away, then just try to keep plants away in the future. Best of luck with KoKo.