What to do to cover a block wall?

Could you grow a heat loving vine on the wall? It would absorb lots of the heat. :)

Yup, I have 2 slumpstone walls in my back yard and once they warm up and get hot, they retain the heat and it just radiates. Paint will peal sooner rather than later and look ticky tacky. Best you can do is choose plants that can withstand the heat. If you can, bring the bed a bit further out into the yard (as long as it will not interfere with any irrigation lines) and choose plants that can withstand intense summer heat. I am in zone 9 and vinca plants or vines will do well as long as they get watered often. At my house it is 100°+ in the shade for months on end so you know how hot it can get in direct sun.

Using a soil that holds water will help your plant do better. A trellis against the wall with jasmine, climbing roses, kiwi or grapes will thrive with the heat. As will a vertical garden attached to the wall of heat loving succulents.

Look ok for plants that handle heat and do well with less watering-zeriscaping. I have a concrete wall and attached a decorative wall fountain with a half circle pond. It has worked for me.

A drip irrigation system to water once or twice a day should keep your garden going.

Could you build a lattice or arbor out from the wall?

I live in low Desert Southwest and have cinder block fence/walls can't get any hotter than this 100-120 degrees in AZ---‎Bougainvillea vines,Climbing Roses,Jasmine,Trumpet vines all work well on the walls & are drought tolerant. Do you want to protect the plants/flowers or just stop the heat coming off the walls or the sunglare? water thoroughly early in the mornings use a good soaking to get ground wet the flowers should love the sun-or maybe you've planted the wrong kind? for your area you are trying to grow them in. I have year round blossoms on mine in full all day sun surrounded by 2 cinder block walls. Where do you live? you don't tell us.let me know for some suggestions on which ones will do best in your situation