There are a few theories why dogs roll in grass but no concrete proof. To watch them roll appears to be pleasing to them regardless if they are rolling in grass or some dead carcass that has been left to rot for days or weeks. For an owner this is sometimes upsetting as well as puzzling. Here are a few theories why dogs roll in grass.
One theory is that it is a built in need to roll in grass or anything that may be available. This is said to come from their cousins the wolf that rolls in grass and dead animals to disguise their own smell. This makes it easier to sneak upon their prey when hunting. Dogs may roll in grass due to this trait.
Rolling off unwanted smells
When you give your dog a bath outside he will immediately head for the grass to have a roll when you release him. Perhaps you think he is trying to get dry faster but maybe he is trying to get rid of the smell of the shampoo you have used to wash him. What smells pleasant to you may not be so pleasant to your best friend.
If you have a yard that extends into a large area you may find your dog choosing a piece of grass that has the worse smell you could imagine. He will roll in this with enthusiasm while you stand there in disbelief. To him he is perhaps reverting back to his ancestry and doing what comes naturally while you are probably thinking of all the clean grass he could have rolled in. For your dog it is the stink that matters.
For the pure joy of it
Dogs will roll in clean grass and do it with abandonment. Maybe they have an itch that cannot be scratched any other way. They will do the same thing in winter when the snow is on the ground. Perhaps they do it for the sheer pleasure or perhaps they are leaving a calling card for any other animal that happens to walk by. When they do roll in grass you can almost feel the pleasure they take in doing this. Perhaps they are doing it for attention. Whatever the reason you have to admit that they are enjoying what they are doing.
Dogs will always be a little perplexing. You may think you know why they do certain things but this only last for a short period of time until they do something totally different to throw you off. Rolling in grass is one of those perplexing actions and you may never know for sure why your dog rolls in grass so enthusiastically.