Ok, here’s the plant shelf done with the stuff I had on hand: a piece of plywood, faux stone spray paint, paracord (for hanging). I already had two hooks in the ceiling so I didn’t bother to make them align with the edges of the shelf. I drilled holes in the four corners of the board and put the paracord through, then tied an overhand knot below to keep it in.
This works okay, but it’s very unstable and I’m not happy with it as a long-term solution. If it’s bumped just slightly, it sways dangerously. If it were bumped a little harder, it could easily dump these three plants onto the countertop. (And that quartz countertop is hard stuff, so the pots would shatter.) So I’m still looking for a better solution for raising my plants off the counter, but still in front of this window.