California’s cannabis harvest season for outdoor-grown plants is dictated by the plant’s sensitivity to light cycles. As a photoperiod-sensitive crop, its transition from vegetative growth to flowering is triggered by the decreasing hours of daylight after the summer solstice. This natural response sets the annual cultivation schedule, culminating in the harvest, which generally runs from spring planting through the fall.
The Outdoor Harvest Calendar
The typical outdoor harvest window in California spans from late September through November. This timing is governed by the plant’s initiation of flowering, which begins as the days shorten and the nights lengthen in late summer. This shift signals to the plant that the growing season is ending and it is time to produce flowers.
Flowering initiation generally occurs in late July or early August across most of the state. Once flowering begins, the plant requires an average of eight to eleven weeks to fully mature its flower clusters, depending on the specific genetics of the strain. Indica-dominant strains often mature faster, allowing for harvest as early as late September or early October.
Sativa-dominant strains, which have longer flowering periods, typically require more time and are often harvested in late October or even into November. This staggered maturation allows farmers to manage the labor-intensive harvest process over several weeks. The goal is to time the harvest precisely when the glandular trichomes on the buds have reached peak cannabinoid and terpene concentration, indicated by their transition from clear to milky-white and then to amber.
Geographic and Climatic Variations
California’s vast and varied geography means the standard harvest calendar is not uniform across all cultivation sites. Distinct microclimates throughout the state significantly influence the exact timing of maturation and the specific risks growers face. Elevation and proximity to the Pacific Ocean are two major factors that create these regional differences.
In the northern coastal regions, such as the famed Emerald Triangle, the combination of cooler temperatures and higher humidity can accelerate the risk of mold and mildew, particularly late in the season. Growers in these areas often aim for an earlier harvest, sometimes by mid-October, to avoid the heavy fall rains that can damage mature buds. The cooler climate can also slightly prolong the overall maturation period for some strains.
Conversely, Southern California’s inland areas and the Central Valley experience a much drier and warmer fall. These conditions are more forgiving, allowing growers to let their plants mature longer, often into November, without the threat of early-season mold or frost damage. The extended warm, dry period is particularly beneficial for late-flowering Sativa varieties to reach their full potential.
Elevation also plays a role, with higher-altitude farms experiencing cooler nighttime temperatures sooner than those at sea level. These lower temperatures can sometimes speed up the plant’s transition to flowering or change the coloration and resin production of the flowers. However, they also bring the threat of frost earlier, which necessitates a more compressed harvest timeline.
Indoor Cultivation and Year-Round Supply
While outdoor harvesting is strictly limited to the fall, a significant portion of California’s total cannabis supply comes from indoor and greenhouse operations, which operate outside of the natural season. These controlled environments ensure a consistent, year-round product availability for consumers.
Indoor cultivators manipulate the photoperiod by using artificial lighting systems that mimic the natural decrease in daylight hours. Growers intentionally switch the light cycle to 12 hours of light and 12 hours of uninterrupted darkness to trigger the flowering stage on demand. This allows for continuous production scheduling.
By managing the environment, these facilities can complete multiple harvest cycles annually, typically achieving between four and six harvests each year. Greenhouse operations often use supplemental lighting and light deprivation techniques, where opaque covers are mechanically deployed to force darkness. This allows for precise control over the flowering cycle even with some natural sunlight, decoupling the supply chain from the seasonal outdoor harvest.