someting plastic

I'm sorry, but "something plastic" might be your only hope. The rooftop will be very hot and windy. The boxes are not wide or deep enough to withhold enough moisture to get much of anything through the day.

I can't think of anything cat proof. Maybe plant something for the cat instead? there is a cat grass you can get seeds for at a pet store.

i have that size on my deck railing with stawberries growing in them for the last 5 years. lots of pruning and i get a few berries.

Have you tried Sedums or Artemesias? Both of them are virtually heat-proof and are very tough. There are many, many different varieties of each so you could design a good-looking display. I used to live in Wyoming where winters are very cold and lots of wind to dry things out and both of these survived very well.

Thanks for the comments. Yes, it sure does get hot up there, but not so windy given that the planters are on the ground and have some sort of wind break somewhere around them.

Today I planted some cute little amazon mist sedge in 3 of the planters. We'll see how they do. Im hopeful since they say "full sun" and they are pretty small so I could get dirt all around them.... they were cheap at Lowes and returnable if/ when I kill them. I cant find them on any list as toxic to cats. Apparently my cats approve as they ran right over to them and started munching before I even got them outside.

For the other planter, Im thinking of some sweet potato vines crawling up on a trellis behind the planter. I think Sweet potato can handle full sun? From what I know, they are pretty easy to grow...

Sedums are a last resort as I was really looking for a plant that moves in the breeze like a grass does. Pretty much whatever I plant I have to assume will die in the winter as there will be no way to keep the soil from freezing solid.

Someone mentioned planting something for the cats specifically. Yes, I will certainly do that in smaller containers. Also, I have made them a patch of grass (sod) to lay in in a 7'x 3' container, so they pretty much got it made!

Happy 4th everyone!