Forgot to mention Sacramento California area. Zone 9B

Euphorbia tirucalli "Sticks on Fire"

Euphorbia lomelli "Slipper Plant"

I used both of these in the LA area. They add texture and color.

There aren't too many things you can plant that aren't going to create constant dirt and maintenance for the pool.

I had similar at a previous home, planted mine with Agapanthus ”Pixie” ( or ”Peter Pan”?) because my planter was narrow, along with a Sago palm in the wider part. I cant tell what your planter’s depth is.

It sounds like you have a great opportunity to create a beautiful and low-maintenance landscape behind your pool wall! There are a variety of evergreen plants that thrive in full sun and require minimal pruning.

One option is to consider using a combination of shrubs and ornamental grasses. Some examples of evergreen shrubs that could work well in your space are the compact varieties of holly, boxwood, or juniper. Pairing them with tall grasses like feather reed grass or blue oat grass can add texture and interest to the space while still keeping maintenance low.

Another option is to consider using vines or climbers to grow up the pool wall. This can create a lush and natural look while still allowing you to utilize the space around the pool. Some evergreen vines to consider are English ivy or Carolina jasmine.