Autoflowering plants are defined by their independence from external light cycles for initiating the flowering phase. Unlike traditional photoperiod strains, which require reduced light hours to flower, autoflowers possess genetics that automatically trigger the transition from vegetative growth to flowering after a specific time period. This self-timing mechanism is inherited from Cannabis ruderalis. The result is a highly predictable and generally much shorter life cycle, making autoflowers an appealing choice for growers seeking a fast turnaround.
The Standard Autoflower Lifecycle Timeline
The autoflower life cycle is largely predetermined by genetics, meaning the answer to how long they grow is time-based. Most strains progress from seed germination to final harvest within 8 to 12 weeks.
The total duration includes a short seedling stage and a vegetative phase lasting three to five weeks. After this age-based threshold, the plant automatically enters the flowering phase, which usually lasts four to seven weeks. While this timeline is reliable for planning, the exact harvest day depends on the plant’s visual maturity rather than the calendar alone.
Key Variables That Impact Growth Duration
Genetics and Strain Type
Although the autoflower timeline is fixed by age, genetic and environmental factors influence the final harvest date. Subspecies dominance determines the overall duration. Sativa-dominant autoflowers generally take longer to mature, sometimes requiring 12 to 15 weeks, while Indica-dominant varieties tend to finish faster, often closer to 8 to 10 weeks.
Environmental Stress
Environmental stress can extend the growth period by slowing down development. Issues like severe temperature fluctuations, nutrient lockouts, or transplant shock can temporarily stall vegetative growth, delaying the onset of flowering. Early-life stress results in a smaller final size and potentially a slightly longer overall cycle to reach full maturity.
Light Intensity and Schedule
The light schedule affects the speed of growth and the plant’s ultimate size, even though it does not trigger flowering. Autoflowers perform optimally under long light periods, such as 18/6 or 20/4. Providing high light intensity maximizes the rate of photosynthesis, allowing the plant to reach its potential size and maturity quickly. Lower light intensity may result in slower development and prolong the time needed to produce mature flowers.
Identifying Peak Maturity for Harvest
Harvest timing depends on observing specific visual indicators, which are more accurate than the general time frame. The most accurate measure of maturity involves inspecting the trichomes, the tiny, mushroom-shaped resin glands covering the flowers. These structures contain the cannabinoids and terpenes that define the final product’s potency and effects.
Trichomes change appearance as they mature, shifting from translucent (clear) to opaque (milky or cloudy), and finally to amber. Clear trichomes indicate the plant is immature and cannabinoid production has not peaked. The milky stage signifies the highest concentration of tetrahydrocannabinol (THC) and is associated with potent, cerebral effects.
The decision of when to harvest is based on the desired effects. Many growers aim to harvest when trichomes are predominantly milky, with 20 to 30 percent having transitioned to amber. The amber appearance signals that THC is degrading into cannabinol (CBN), which is desired for its more sedative and body-focused qualities.
Secondary indicators support that the plant is nearing its end of life. The white, hair-like pistils on the flowers will recede and change color to a dark red or brown. Additionally, the large fan leaves often begin to yellow and drop off, a natural process known as senescence, as the plant pulls stored nutrients to complete the final ripening.
Effects of Delaying the Harvest
Allowing the autoflower to continue growing past its peak harvest window initiates the natural degradation of compounds within the resin glands. The most significant consequence of delaying harvest is the conversion of THC into CBN. This transformation occurs through oxidation, where the THC molecule breaks down when exposed to light and air.
When a high percentage of trichomes turn amber, the resulting flowers exhibit increased levels of CBN, leading to a noticeable shift in effects. This over-ripeness generally reduces perceived potency and produces a more relaxing or sedating experience. Furthermore, leaving the mature plant standing too long, especially in humid conditions, increases the risk of mold or bud rot developing.