Maybe some sort of succulent? Cactus?

Best bet is to move the planter into part shade.

Sprengeri fern? It's pretty tough...

I thought the flowers blooming in the head looked quite good for having made it through the summer! I second the Sprengeri fern. But for bloomers...

Have you tried filling the head with water and setting a pot of trailing-type bloomer in it?

I've had success with setting bloomers in water all summer, grouping them in a bowl (6" deep black plastic salad bowl repurposed from a catered meal) sitting in a pottery pot which is on a wood stump). Easy enough to tip the plastic container, dump and refresh the water to avoid growing mosquitoes.

If I had a pottery head and wanted blooming in hot summer, I would find or make-to-fit a container with drainage holes, fill the head with water, and set the planted container in it. No dumping needed, just checking water level now and then.

If I had duplicate containers, I would plant each with a different type plant and rotate the best looking one into the head.

But, I like to fiddle and rearrange, and maybe you don't!