Grass-widower?

Norwegian has lots of interesting words. One of the big bookstore chains, Norli, has as its motto "Ord: sukkertøy i munnen" ("Words: candy in your mouth"), and I've always liked the sound of that. Every now and then I meet a new word that intrigues or amuses me. Tomorrow night I'm going over to a friend's to have our second annual Christmas beer tasting; we had it last year when Inki was on a girls' shopping trip to London. This time it's the other two tasters, Ole Kristian and Hein, who are "gressenkemenn," literally "grass-widowers" but actually temporary bachelors since their wives are out of town. So, I ask, where does the "grass" come from? How does grass temporarily deprive someone of their spouse? Is it like being a football widow on NFL Sundays?

Just wondering...