This is from Mandala site ...
A popular method is to flush soil with large amounts of water towards harvest time. Some growers believe this is necessary to rinse out unsavoury minerals or substances which may otherwise negatively influence the flavour of the crop. Whereas flushing substrates with pure water is conducive, and indeed necessary, in hydroponics - it is quite dangerous when applied to containers filled with soil. Hydroponic substrates are very porous and drain quickly so that a high air-to-water ratio is quickly reestablished. But waterlogged soil requires days if not an entire week to dry. It drowns the root zone, thereby completely depleting it of oxygen. Anaerobic bacteria quickly spread leading to a high risk of fusarium. In the meantime, the plant absorbs a large amount of water until the tissues are bloated with water and begin to „sweat". Within the dense buds the internal humidity rises to extremely high levels, so that when you touch the interior your fingers are moist. All factors combined can trigger bud mold within hours of flushing, after which it spreads throughout the flowering colas. We have regularly observed growers reporting bud mold 1-2 days after rinsing their soil based plants. The correct approach to watering cannabis on soil during the last 2 weeks of flowering is to reduce watering as much as possible without interfering with plant health (ie. avoid thoroughly dried up pots and prolonged periods of droopy leaves on plants). Especially if high humidity persists this is one of the most secure methods to avert bud mold. Always water shortly after lights go on. For outdoor, water before noon time. The top layer of the soil should be dry by the time the dark period starts.
