Europeans have window boxes everywhere! They are pros.

You would put screws through the bottom of the box into the ledge. If the ledge is brick or cement you would need to use masonry anchors. I’d recommend securing the wooden window box and then dropping in a plastic liner or pots if the window box doesn’t come with one. That way you can remove the plants and soil easily if needed to check/fix the attachments.

We have a second floor window with a 7 inch ledge (about 45 inches long). I wanted to get a window box but don't see an any way to secure it. It's directly above a basement door so I wouldn't want to risk it ever falling off. Anyone know of boxes that I could get or different ways of securing them?