The final two weeks of the flowering cycle represent a sensitive and important period that directly determines the finished quality of the harvest. During this time, the plant shifts its energy entirely toward the ripening of its flowers, intensifying the production of cannabinoids and aromatic terpenes. Management decisions regarding nutrients, environment, and timing are critical to maximizing the plant’s genetic potential just before harvest.
Visual Changes and Maturation Signs
The most obvious signs of approaching maturity are physical transformations occurring in the floral structures. Buds undergo a final period of significant swelling, increasing their density and mass. This fattening stage clearly indicates the plant is nearing the end of its life cycle.
A highly noticeable change involves the pistils, the delicate, hair-like structures emerging from the buds. Initially white, these pistils begin to darken, curling inward and changing color to shades of red, orange, or brown. When roughly 50 to 70 percent of the pistils have changed color, it signals the final ripening phase.
Simultaneously, the large fan leaves will begin to yellow and fade, a process known as senescence. This occurs as the plant mobilizes stored nutrients, particularly nitrogen, from the leaves back into the developing flowers. This fading is a desirable and healthy sign in the final weeks, showing the plant is drawing down its internal reserves in preparation for harvest.
Nutrient Management and Flushing
The practice of “flushing” involves replacing the nutrient solution with plain, pH-balanced water during the last 7 to 14 days before harvest. The rationale is to encourage the plant to consume residual mineral salts and stored nutrients from its tissues. This process is believed to result in a cleaner, smoother final product with a less harsh taste and improved aroma.
The duration of the flush varies; soilless media like coco coir or hydroponics often require 7 to 10 days, compared to soil, which may need up to two weeks. To ensure effectiveness, the volume of water used should be substantial, typically two to three times the container size, allowing the water to fully saturate the medium and drain out.
Monitoring the effectiveness of the flush involves measuring the electrical conductivity (EC) or parts per million (PPM) of the runoff water. Using a handheld meter, the runoff value should be monitored until it drops significantly, ideally near the PPM of the plain water input. A decreasing runoff PPM confirms that the concentration of dissolved nutrient salts in the root zone is successfully reduced.
Environmental Control During Final Ripening
Adjusting the environmental conditions in the grow space significantly influences the final characteristics of the flowers. Lowering the relative humidity (RH) is important during the final two weeks to prevent mold and bud rot in the dense floral clusters. Maintaining the RH between 30 and 40 percent minimizes the risk of pathogen development.
Lowering the temperature is a common tactic used to enhance resin production and encourage color expression. In the final weeks, daytime temperatures can be reduced to 18–24°C (64–75°F), with a further drop during the dark cycle. These cooler conditions mimic the natural onset of autumn, which stresses the plant slightly to increase terpene and resin synthesis.
Some growers implement a final 24- to 48-hour period of complete darkness immediately before harvest. While scientific evidence is not conclusive, this practice is theorized to cause a final spike in resin production as the plant attempts to protect itself from perceived environmental stress. If this technique is employed, temperature and humidity must remain stable and cool to avoid creating conditions favorable for mold.
Determining the Precise Harvest Window
While the visual cues of darkening pistils and yellowing leaves offer a good estimation, the definitive method for determining the optimal harvest time is by inspecting the trichomes. These resin glands are the factories where cannabinoids and terpenes are synthesized. A magnification device, such as a jeweler’s loupe or a digital microscope, is required to accurately assess their maturity.
Trichomes progress through three main stages of development, indicated by their clarity. They begin as clear, indicating that cannabinoid content, particularly tetrahydrocannabinol (THC), is still low. They then transition to a cloudy or milky white color, which signals the peak concentration of THC. Harvesting when most trichomes are cloudy typically yields a more potent and energetic effect.
The final stage involves the cloudy trichomes turning amber or brown. This coloration indicates that THC is beginning to degrade into cannabinol (CBN), a cannabinoid associated with more sedative or relaxing effects. The preferred ratio of cloudy to amber trichomes is a matter of personal preference. Many growers aim for a mix, often around 70 percent cloudy and 30 percent amber, to achieve a balance of potency and body effect.