As part of the Great Green Wall initiative, Senegal has been building circular, drought-resistant gardens to keep the Sahara desert from spreading any further. The Kid Should See This explains how they work:
These Senegalese farmers plant the spiraling gardens with a plan to hold water: Medicinal plants in the inner circle, three rows of vegetables, with fruit and nut trees next. The outer circles are created with large baobab trees and African mahogany trees.