There's an area in our backyard that is mostly rocks, trees and weeds.

Perhaps a few pots with flowers and or vegetables growing in them could add color and some greenery. Just make sure the pots have good drainage You could do a grouping of two or three together. I recently got some old oil barrels cut them in half with a metal grinder and planted in them this summer. I had to drill the bottoms for drainage. The plants are doing well and the barrels have a rusty used look that is a little different. And the barrels were free. So look at upcycling some old barrel, washtub etc

Hello Linda, When in Rome . . . Try adding more rocks maybe even in groupings or around a bird bath. Also you could use the trees to hang things from. Maybe a wind chime, or hanging pots with flowers and greenery hanging over the sides. Or maybe a swing (or a swing bed). Hope this helps you. Good luck.

hello, if you can get onto pinterest they have some great garden ideas (Rock Garden). maybe you could create a fairy garden if you want to create something different.

https://www.pinterest.com/explore/landscaping-a-slope/?lp=true

Maybe working towards a terraced garden that you could develop over time. See what kinds of perennials grow well in your area, plant them in a row or group and see how you like it. Do some research on terraced gardening to see the what style will work with your home and surrounding landscape. Good luck!