Most veterinarians (including myself) recommend feeding adult dogs twice a day. Some people feed their dogs once a day, but dogs that are only fed once a day can get hungry and also sometimes can be prone to bilious vomiting (vomiting caused by an empty stomach).
No one really knows why dogs eat grass. The majority of experts agree that it is not a cause for concern. Many dog parents will notice that their dogs occasionally graze on grass while out on a walk or in the backyard. Most of the time, there is very little cause for concern for this behavior. Wild canids are frequently seen eating grass in their natural habitat.