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The cultivation practice of running only plain water through cannabis growing media before harvest to remove nutrient residue.
Flushing is the practice of watering cannabis plants with only plain water (no nutrients) for a period before harvest. The goal is to allow the plant to use up stored nutrients in its tissues, which growers believe produces a cleaner, smoother final product with better flavor and a white ash when smoked.
Most growers flush for one to two weeks before harvest, though the exact duration depends on the growing medium. Soil-grown plants may need a longer flush (10 to 14 days) because soil retains nutrients, while hydroponic and coco coir setups can be flushed effectively in 5 to 7 days since there is no nutrient reserve in the medium. During flushing, the plant draws on stored nutrients in its leaves, often causing a yellowing of fan leaves that some growers view as a sign of a successful flush.
Flushing is one of the most debated topics in cannabis cultivation. A 2020 study from RX Green Technologies found no significant difference in mineral content, yield, or potency between flushed and unflushed cannabis. Some experienced growers have moved away from extended flushes based on this research. Others maintain that flushing improves the subjective smoking experience based on years of personal observation. Whether or not you flush aggressively, proper drying and curing have a more documented impact on final product quality.
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