No Dead Grass Involved in a Grass Widow

A reference to a woman as a "grass widow" has nothing to do with grass and, actually, usually nothing to do with being a widow either.

While the definitions can vary regionally, a grass widow can be a woman whose husband is absent for long periods of time, a woman who is completely separated from her husband, or a woman who was never married to a now absent boyfriend (or father of her child). 

It does not mean her husband is dead.

And it does not mean she was married to a now-deceased man whose last name was Grass.