A root-zone flush is a corrective leach: you pass several times the container volume of low-EC, pH-adjusted water (or a dilute nutrient solution) through the medium to dissolve and wash out salts that have built up. It resets runoff EC and pH so the roots see a predictable solution again.
In practice
When it's justified:
- runoff EC well above input, for example 1.0 mS/cm or more higher, and rising;
- suspected lockout or salt burn with pH and root health checked;
- after a feeding error or a switch of nutrient line.
How growers usually do it: run about 2-3 times the pot volume, pH-adjusted to the medium. In coco, flush with a mild, balanced solution (around 0.5-1.0 mS/cm) rather than pure RO to keep the buffer stable. Then check runoff EC and pH and resume normal feeding.
House position: this is the one valid use of "flushing". It treats the medium, not the plant, and can be done at any stage. It is not a pre-harvest ritual.
Don't confuse with
- Pre-harvest flushing: plain water before harvest to "clean" the plant (Myth, harmful).
- Watering to runoff: routine practice, not a reset.
- Reservoir change: swapping hydro solution, not leaching a medium.
Runoff is the water or nutrient solution that drains out of the bottom of a container after irrigation; growers test it to see what is happening in the root zone.EC (electrical conductivity) measures how well a solution conducts electricity, a proxy for total dissolved salts; growers read it in mS/cm to gauge nutrient strength.pH measures how acidic or alkaline a solution is on a 0–14 scale; in growing it controls nutrient uptake, with soil best near 6.0–7.0 and hydro 5.5–6.5.mS/cm (millisiemens per centimetre) is the standard unit of EC for nutrient solutions; 1 mS/cm equals 1 dS/m and 1,000 µS/cm.Pot size is the volume of medium a plant roots into; bigger pots give bigger plants within reason, but feeding frequency can let small pots punch well above their size.Feeding only plain water for days or weeks before harvest to "clean" the plant; GenetixBay rates it a Myth that harms yield, unlike a root-zone salt flush.RO water is water stripped of most dissolved salts by reverse osmosis; it has near-zero EC and little buffering, so pH moves easily and Ca and Mg must be added.Watering to runoff means applying enough water or solution that some drains from the bottom of the container, typically 10-20% of the volume applied.Nutrient lockout is when plants show deficiency symptoms although nutrients are present, because pH, salt build-up, ion antagonism or damaged roots stop uptake.
