Industrial hemp, a variety of the Cannabis sativa L. plant, is legally defined by its low concentration of delta-9-tetrahydrocannabinol (THC), typically below 0.3% on a dry weight basis. This distinction determines its use for fiber, seed, or cannabinoid extraction. The time it takes for hemp to grow from seed to a mature, harvestable crop varies significantly, generally spanning 70 to 140 days. This wide timeline is influenced by the specific end product desired, the variety planted, and the environmental conditions it experiences.
Key Factors Influencing Growth Speed
The speed of hemp growth is largely determined by the plant’s genetic blueprint. Hemp varieties bred for fiber are typically quick-growing, focusing on tall, slender stalks, and reaching harvest maturity faster than other types. Conversely, strains developed for high concentrations of Cannabidiol (CBD) or other cannabinoids are often slower to mature, dedicating more time to flower and resin development. “Autoflower” varieties represent a genetic shortcut, as they are bred to transition to flowering automatically after a set time, maturing in approximately 75 days.
Environmental conditions play a substantial role in maximizing the plant’s genetic potential. Hemp requires long hours of intense sunlight, ideally 12 to 18 hours per day during the early growth phase, and performs best when soil temperatures are consistently above 50°F (10°C). Water availability and nutrient delivery are also crucial, as the plant needs high levels of nitrogen, phosphorus, and potassium. Fluctuations in temperature or inadequate light can slow vegetative growth, extending the overall time to harvest.
The method of cultivation also impacts the time to maturity, particularly concerning light exposure. Hemp is a photoperiod-sensitive plant, meaning its transition from the growth phase to the reproductive (flowering) phase is triggered by decreasing daylight hours in late summer. Outdoor cultivation is thus subject to the seasonal photoperiod. Indoor or greenhouse environments allow growers to manipulate the light cycle, artificially shortening the light period to induce flowering sooner and potentially accelerating the final stage of the growth cycle.
The Hemp Growth Timeline: Stages and Duration
The hemp life cycle begins with germination, the shortest stage, which typically takes between 3 to 7 days under suitable conditions. The seed absorbs water and heat to activate the embryo, developing a taproot and two small cotyledon leaves. This initial phase is highly dependent on consistent moisture and warmth.
Following germination, the plant enters the vegetative growth stage, a period focused on producing stems, leaves, and roots, which can last from 4 to 12 weeks. This is the phase of most vigorous growth, where the plant can grow several inches per day under optimal light and nutrient conditions. Farmers growing for fiber aim for a long vegetative period to maximize stalk height and biomass, often resulting in plants 6 to 7 feet tall.
The flowering, or reproductive, stage is initiated when the days become shorter, typically in late summer or early autumn for outdoor crops. This phase generally lasts between 4 and 6 weeks, though it can extend longer for certain CBD-focused varieties. During this time, vertical growth slows down significantly as the plant diverts its energy into producing flowers, which are the source of seeds and cannabinoids. For CBD production, this period involves the development of trichomes, the sticky, hair-like structures that contain the highest concentration of cannabinoids and terpenes. The timing within the flowering stage is particularly sensitive for CBD growers because cannabinoid levels rise as the flower matures. Harvesting too early means lower potency, but waiting too long risks degradation of the compounds or the THC content rising above the legal limit.
Harvesting and Final Growth Metrics
The final determination of harvest time is dictated by the specific commercial product the hemp is being grown for. Hemp grown for fiber is harvested earliest, often ready in approximately 60 to 90 days after planting, at the onset of flowering. At this point, the stalks have reached their maximum height and the fibers are most pliable, before the stem begins to lignify, or become woody. This early harvest maximizes the yield of soft, high-quality primary fibers.
Hemp grown for seed, which is used for oil and food products, requires a longer time frame to allow the seeds to fully mature. This harvest usually occurs between 105 and 150 days after planting. Farmers typically wait until 70% to 80% of the seeds are mature and firm to the touch, and the bracts surrounding the seeds begin to dry and open.
The longest growth cycle is typically reserved for hemp cultivated for floral material and CBD extraction, with harvest occurring 3 to 4 months after planting. This delay ensures the flowers have fully developed their resin glands, or trichomes, which contain the highest concentration of cannabinoids. Growers monitor the color of the trichomes for a milky-white appearance, signaling the optimal peak of maturity and potency before the compounds begin to degrade.