SANTA YNEZ VALLEY, Calif. — It is the fall harvest here in this fertile stretch of oaks and hills that produces some of the country’s best wine. This season, though, workers also are plucking the sticky, fragrant flowers of a new crop.

Marijuana is emerging among the vineyards, not as a rival to the valley’s grapes but as a high-value commodity that could help reinvigorate a fading agricultural tradition along the state’s Central Coast. Brushed by ocean breeze, cannabis has taken root, offering promise and prompting the age-old question of whether there can be too much of a good thing.