The final stage of plant cultivation before harvest is known as “flushing,” a process designed to improve the quality of the final product. Flushing involves substituting the nutrient solution with plain, pH-balanced water for a specific period. This practice forces the plant to metabolize and consume stored mineral salts and excess nutrients within its tissues. The primary goal is to ensure a cleaner, smoother, and better-tasting harvest by preventing harshness from residual compounds.
Defining the Flushing Phase and Timing
Flushing aims to deplete nutrient reserves accumulated over the growth cycle. Plants naturally store mineral salts, which can negatively affect the final product’s flavor and smoothness. By withholding external nutrients, the plant enters a catabolic state, drawing on internal storage to complete maturation.
The timing of the flush is determined by the plant’s anticipated harvest window, typically beginning when the plant is close to peak ripeness. This phase is initiated between 7 and 14 days before the expected harvest date for most cultivated plants. The exact duration depends on the specific plant strain, its overall health, and the type of growing medium used. Growers often monitor the plant’s trichomes, beginning the flush when these structures start transitioning from clear to a milky color.
Establishing the Watering Frequency During the Flush
The act of flushing involves both withholding nutrients and actively washing the growing medium. Therefore, watering frequency is not based on a strict daily schedule, but rather on achieving high-volume saturation. Flushing requires irrigating with a significantly larger volume of plain water than a typical feeding, often three to five times the usual amount. This heavy application facilitates maximum runoff, which should be between 20 to 30 percent of the total volume applied.
This high-volume approach physically washes accumulated mineral salts from the root zone, effectively resetting the medium’s composition. The frequency of saturation is determined by how quickly the medium dries out after the flush. Growers must monitor the pot’s weight or check the substrate one to two inches deep to confirm it is sufficiently dry before the next watering. Waiting for the medium to dry slightly encourages the plant to continue pulling water and utilizing its internal nutrient stores.
This differs significantly from the nutrient-rich schedule, where the goal was steady, consistent feeding and growth. During the flush, cycles of saturation and drying are used strategically to leach out salts and stimulate the plant’s internal consumption. If the medium remains saturated for too long, the roots can be deprived of oxygen, leading to stress. The goal is to allow the root zone to dry just enough to stimulate water uptake without causing the plant to wilt.
Medium-Specific Watering Adjustments
The physical properties of the growing medium dictate the specific frequency and overall duration of the flush. Soil-based substrates naturally retain a greater volume of water and nutrients due to their density and organic matter content. For plants in soil, the flush generally lasts longer, typically between 10 to 14 days, with watering occurring less often. Watering is often required only every two to four days, allowing the soil to nearly dry out between applications to prevent over-saturation.
In contrast, inert media such as coco coir and rockwool have excellent drainage and hold less water, meaning salts are removed faster. Plants in these substrates require a shorter flush, often lasting only four to seven days. The watering frequency is much higher, typically daily or every other day, to maintain consistent moisture and rapidly leach the salts. This frequent, high-runoff watering ensures the quick replacement of the nutrient solution with pure water.
Hydroponic Systems
Hydroponic systems, including Deep Water Culture (DWC) or recirculating setups, require the most immediate adjustment. The flushing process is typically very short, lasting only one to two days. This involves draining the reservoir and refilling it with plain, pH-adjusted water to immediately cut off the nutrient supply. For these systems, flushing is a continuous process of the roots drawing from a pure water bath for the final 24 to 48 hours before harvest.