Use the dropdown “notifications” button on the top righthand side of the group page to select “turn off notifications.”
This means that when you visit the group’s page, you’ll see all the posts, but none will be appear in your feed, except when Facebook acts a little wonky. You also will NOT get pinged every time someone posts something new to the group.
We highly recommend that you protect your work (and rest) hours by turning off notifications for all Facebook groups! This slideshow shows you how to do it (and provides a few more timesavers, as well.)