Home gardens have been vital to human societies for thousands of years: from clusters of beneficial trees and shrubs planted on forest edges in pre-historic times, to the lush edible gardens grown traditionally in many tropical regions, to the tiny, densely planted backyards that dot cities worldwide.

Roughly 24% of the world’s land area is degrading, including more than a fifth of the cropland and nearly a third of the forests – yet 1.5 billion people directly depend on degraded areas....