Flushing is a common technique in horticulture that involves supplying a plant with pure water or a non-nutritive solution in the final days before harvest. This process is intended to deplete the nutrient reservoir within the growing medium and the plant itself. When growing in coco coir, this final preparation step is modified due to the medium’s distinct characteristics. The goal is to encourage the plant to consume its stored nutrients, resulting in a cleaner, smoother final product.
Understanding the Purpose of Flushing in Coco Coir
The primary reason for flushing is to remove accumulated mineral salts from the root zone and encourage the plant to use its internal nutrient reserves. Mineral salts build up in the coco coir medium throughout the growth cycle, which can lead to a harsh taste if not addressed before harvest. Flushing essentially starves the plant of external nutrition, forcing it to mobilize and consume compounds stored in its leaves and tissues.
Coco coir functions more like a hydroponic medium than traditional soil. It is relatively inert, providing little inherent nutrition, and has a lower buffering capacity. This allows for rapid changes in the root zone’s nutrient concentration. The medium’s high cation exchange capacity (CEC) allows it to hold onto nutrients efficiently, but also requires specific attention to salt removal. Because of these properties, flushing in coco coir is generally faster and more effective than in soil.
Determining the Ideal Time to Start Flushing
The decision of when to begin flushing is based on visual cues and a planned harvest date. Growers must estimate the time remaining until peak maturity to avoid flushing too early, which can reduce final yield and quality.
A common visual indicator is observing the plant’s maturity through the development of trichomes on the flowers. When the majority of trichomes have turned cloudy and a small percentage (5% to 15%) have turned amber, the plant is typically entering its final harvest window. Furthermore, a natural yellowing or senescence of the fan leaves suggests the plant is nearing its natural end. This occurs as the plant draws stored nutrients, like nitrogen, from the foliage, indicating it is ready to be deprived of external feed.
The Critical Duration: How Long to Flush in Coco
The recommended duration for flushing plants in coco coir is typically 5 to 7 days, though some growers may extend this to 10 days. This compressed timeframe is possible because coco coir is a soilless medium. Its rapid drainage and minimal organic matter allow pure water to quickly leach salts from the root zone.
The specific duration is influenced by several variables, including the plant’s strain and the concentration of nutrients used during the flowering cycle. A plant that received a heavier feeding regimen may benefit from a longer flush to ensure all accumulated salts are cleared. Conversely, a plant fed more lightly may only require five days. Environmental conditions, such as temperature and humidity, also affect how quickly the plant metabolizes its reserves, impacting the overall flush duration.
Practical Methods for Monitoring Flush Effectiveness in Coco
The most reliable way to confirm the flush is effectively removing mineral salts is by measuring the Electrical Conductivity (EC) or Parts Per Million (PPM) of the runoff water. EC measures the concentration of dissolved salts in the solution, providing an objective metric of the nutrient level in the medium. This requires using an EC meter to test the water draining from the pot.
To initiate the flush, use a large volume of plain, pH-balanced water to thoroughly saturate the medium, aiming for 20% to 30% runoff. The runoff EC should be tested and compared to the EC of the input water. A successful flush aims to bring the runoff EC down to a level very close to the pure water used for irrigation. For most growers, this target is around an EC of 0.2 to 0.4 mS/cm, or a PPM of 100 to 200, which confirms the medium is relatively free of nutrient salts.