While I am waiting for this particular rubbish to come my way, I have unearthed another piece of rubbish, or rather two. I have no idea what they are. Someone gave them to me a few years ago, and I have saved them to use as planters.
So first of all I put some air-drying clay into each. White tack would work too. Then I put a drop of glue into each planter and covered with coffee-grounds, for compost. It was just as messy as real planting.
Then I planted the flowers. I don't remember where these come from, most likely a job lot because I wouldn't have bought them for their own sake. I am not good at flowers, so maybe they are wrong for window boxes. Maybe they are climbers or whatever. But it's too late.
Now to the box itself. I considered various models (until I have wrought-iron ones), and I found some bits of angle moulding. Putting two bits together made a perfect window box. I glued on craft sticks on the sides, and for consoles I used bits of fancy coving.
I am not absolutely sure yet which windows will have these boxes. I only have two sets of planters, but then all boxes don't have to be exactly the same, do they? Tentatively, they are on the ground floor.