When Esther Hayden moved into her Seven Oaks home in 1990, the hillside in her backyard — similar to many found throughout Rancho Bernardo — had mostly ground cover and was spotted with a few trees.

Planting on any sloped land is more difficult than flat-ground planting because: 1.) it’s harder to walk and work on a slope; and 2.) the soil is usually poor and thin from erosion. Toughest of all is ...