Nairobi, June 8 -- If Margarita Nyambura could speak to her 12-year-old self, the girl who used to stop by a prison fence each morning to pick orange and yellow flowers, she would tell her to keep going.

Growing up in Embu, where her father was the auditor in charge of Eastern Province, Margarita lived a relatively privileged life. The family compound was tended by gardeners who maintained tidy, traditional plantings. The grass was always neatly trimmed, and her mother planted flowers, too-the common types that filled most homes those days.

What intrigued her even more were the improvised gardens created by police officers nearby. Old bathtubs had been transformed into planters, teaching her an early lesson that would stay with her for ...