The final stage of cannabis cultivation involves nutrient cessation, often called “flushing.” This technique requires growers to completely stop feeding the plant synthetic or organic nutrient solutions. Instead, the plant receives only pure, pH-balanced water for a defined period immediately before harvest. The primary goal of this intentional deprivation is to improve the finished product’s quality, enhancing the flavor, aroma, and overall smoothness of the final flower.
The Purpose of Nutrient Cessation
Stopping the nutrient supply forces the plant to undergo a metabolic shift in its final days. Throughout the flowering cycle, mineral salts and other chemicals from nutrient solutions can accumulate within the plant’s tissues and growing medium. When the external nutrient source is removed, the plant begins to draw upon and metabolize these stored reserves to complete its maturation process. This internal consumption of stored compounds, particularly nitrogen, helps to break down residual salts and excess chlorophyll. The removal of these residual compounds results in a cleaner, less harsh smoke or vapor when the flower is consumed. Successfully flushed buds often produce a light gray or white ash, which many cultivators associate with a purer product, as opposed to the dark, black ash seen from products with high mineral residue.
Determining the Cessation Timeline by Medium
The precise moment to stop feeding depends heavily on the type of material used to grow the plant. The growing medium’s ability to hold onto nutrients, known as its nutrient retention capacity, dictates the length of the flushing period. A longer flushing window is required for mediums that naturally retain more mineral salts, while shorter periods are necessary for inert systems.
Hydroponics
For plants grown in hydroponic systems, such as Deep Water Culture (DWC) or Nutrient Film Technique (NFT), the cessation timeline is the shortest, ranging from 48 hours to seven days. These systems use inert media or no media, meaning the plant feeds directly from the water reservoir. Because the roots are constantly bathed in a fresh, low-nutrient solution, the concentration can be quickly reduced, allowing for a rapid cleanse of the plant’s system.
Coco Coir
Coco coir requires an intermediate flushing period, typically lasting seven to ten days. Although considered inert, coco coir retains some residual nutrients, particularly calcium and magnesium, more than a pure water hydroponic setup. The excellent drainage allows for a faster flush than traditional soil, but the slightly higher nutrient retention capacity means a slightly longer period is needed.
Soil
The longest duration is required for plants grown in true soil or organic soil mixes, with a recommended cessation period of 10 to 14 days or sometimes longer. Natural soil mixes contain living biological activity and possess the highest nutrient retention capacity. The organic matter and clay particles in soil bind to nutrient ions, requiring a more extended period of plain water application to fully exhaust these internal reserves. Attempting a shorter flush risks leaving behind significant amounts of mineral residue, which can negatively impact the final product quality.
Monitoring Plant Readiness Through Visual Cues
While a calendar-based timeline provides a good starting point, visual observation of the plant confirms the success of the nutrient cessation. The most apparent sign the plant is consuming its internal stores is leaf senescence, the natural process of leaf tissue degradation. This process begins with the large, older fan leaves at the bottom of the plant, which will start to yellow and fade as the plant mobilizes stored nutrients like nitrogen and moves them to the developing flowers. A successful flush should produce a beautiful fade across the entire plant. However, it is important not to start the cessation too early, which can prematurely starve the flowers and stunt final development.
Trichome Maturity
The most precise indicator is the maturity of the trichomes, the tiny, resinous glands covering the flowers. Growers use a jeweler’s loupe or a microscope to examine the color of these trichome heads, which transition through three distinct stages.
Initially, they appear clear, indicating immaturity and low cannabinoid content. They then turn cloudy or milky white, signaling the peak concentration of active compounds, including THC. Finally, they turn amber, which indicates that THC is beginning to degrade into other compounds, leading to a more sedative effect. Most cultivators aim to harvest when the trichomes are predominantly cloudy, often a ratio of 70% cloudy to 30% amber, confirming the cessation period has aligned with the flower’s peak maturity.