# Root-zone flush

> Running a large volume of low-EC water or mild solution through the medium to wash out accumulated salts; it treats the medium, not the plant, and suits any stage.

- Canonical: https://genetixbay.com/knowledge/glossary/root-zone-flush.html
- Also written: root zone flush, salt flush, medium flush, leach, flush the medium, salt build-up flush, reset flush
- Glossary category: Harvest, drying and curing · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

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](https://genetixbay.com/knowledge/glossary/runoff.md) [EC](https://genetixbay.com/knowledge/glossary/ec.md) and [pH](https://genetixbay.com/knowledge/glossary/ph.md) 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](https://genetixbay.com/knowledge/glossary/ms-cm.md) 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](https://genetixbay.com/knowledge/glossary/pot-size.md), pH-adjusted to the medium. In coco, [flush](https://genetixbay.com/knowledge/glossary/flushing.md) with a mild, balanced solution (around 0.5-1.0 mS/cm) rather than pure [RO](https://genetixbay.com/knowledge/glossary/ro-water.md) 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.

## Related terms

[Flushing](https://genetixbay.com/knowledge/glossary/flushing.md), [Runoff](https://genetixbay.com/knowledge/glossary/runoff.md), [EC](https://genetixbay.com/knowledge/glossary/ec.md), [Nutrient lockout](https://genetixbay.com/knowledge/glossary/nutrient-lockout.md)

## Read more

- [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md)
- [Pre-harvest flushing: a myth that costs you yield and resin](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)

## Sources

1. Alden MJ, Faust JE. 2025. Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis. HortScience 60(10):1818-1825. https://doi.org/10.21273/HORTSCI18752-25
2. Hershkowitz JA. 2024. Nutrient management of cannabis in controlled environments. MS thesis, Utah State University (Bugbee lab). https://digitalcommons.usu.edu/etd2023/178