Flushing cannabis plants means running pH-adjusted water through the growing medium to carry out leftover nutrient salts before harvest. The water itself matters: tap water at the wrong pH can leave residue behind and stall the flush, so most growers set the pH first and measure the runoff as they go. This guide covers the target ranges, how much water to use, and how to tell when the job is done.
Flush vs No Flush Marijuana: Comparing Effects
Key Features
- Target range of 6.0 to 6.5 for soil grows and 5.8 to 6.2 for coco coir and hydroponic media
- Adjust pH after mixing, since additives and calmag shift the reading
- Plan on roughly two to three times the pot volume in water for a full flush
- Use clean, room-temperature water; let chlorinated tap water sit out first
- Check runoff pH and EC to confirm salts are actually leaving the medium
- Pair with a stop in feeding about 7 to 14 days before harvest
- Works with hand watering, drip lines, or a dedicated flushing solution
What is pH water made of?
In practice, flushing water is just clean water plus a pH adjuster. Reverse-osmosis or filtered water gives you a blank starting point near neutral, which makes the adjustment predictable; hard tap water works too but usually needs more acid to come down. Most growers use a phosphoric- or citric-acid based pH down, add it a few drops at a time, stir, and re-check with a calibrated meter or drop kit. Never trust a reading taken before all additives are in the container, and recalibrate your meter between runs so the numbers you are chasing are real.
How much water should I run through?
A common approach is two to three times the volume of the container, poured slowly in stages so the medium actually absorbs it rather than channelling down the sides. Collect the runoff and test it.
flushing cannabis in hydroponic system before harvest
Can I flush with plain tap water?
Yes, as long as you pH it first and the water is not excessively hard. If your tap sits above roughly 250 ppm, filtered or reverse-osmosis water gives you tighter control.
comparison of flush vs no flush marijuana effect
How do I know the flush is finished?
Runoff pH should land inside your target range and runoff EC should be close to the input water. If EC is still climbing out high, keep going in smaller volumes.
Orders ship discreetly in plain packaging with no product names on the outside, and everything is packed to state compliance rules. Unopened items can be returned within 30 days, and if a pH meter or kit arrives damaged, contact us and we will replace it.