# Flushing

> 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.

- Canonical: https://genetixbay.com/knowledge/glossary/flushing.html
- Also written: flush, pre-harvest flush, preharvest flush, flushing before harvest, final flush, plain water flush, flushed
- Glossary category: Harvest, drying and curing · Evidence: Myth
- 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"

Flushing, in cannabis lore, means stopping all nutrients and giving only plain water (often large volumes) for the last one to three weeks before harvest. The claim is that it removes stored nutrients, improves taste and gives white ash. The plant doesn't work that way. Cannabis is a bioaccumulator: what it takes up is built into tissue, and plain water in the final days doesn't wash it out.

## In practice

House position (Myth): flushing is for toilets. Pre-harvest flushing is actively harmful, not just useless. It starves the plant in its most critical phase, when it's packing on most of its final weight, [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) and resin. Controlled studies found no taste or quality benefit (Alden & Faust 2025; Hershkowitz 2024). Losses grow with how long and hard the plant is starved; some elements even rise in flower tissue after a flush, a concentration effect.

What to do instead:
- **Taper nitrogen**: cut N back toward zero near the finish while feeding P, K, Ca, Mg, S and [micros](https://genetixbay.com/knowledge/glossary/micronutrient.md).
- **Dry and cure properly**: that's where taste and smooth smoke come from.
- **Root-zone flush only for salts**: that treats the medium, at any stage.

## Don't confuse with

- **Root-zone flush**: washing [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md) out of the medium, valid at any stage.
- **Nitrogen taper**: the GenetixBay alternative.
- **Leaching**: routine [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) in [drain-to-waste](https://genetixbay.com/knowledge/glossary/drain-to-waste.md).

## Myth check

Myth, and harmful. Full evidence in [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md); see also [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md).

## Related terms

[Root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md), [Nitrogen taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md), [Harvest window](https://genetixbay.com/knowledge/glossary/harvest-window.md), [Senescence](https://genetixbay.com/knowledge/glossary/senescence.md)

## Read more

- [Pre-harvest flushing: a myth that costs you yield and resin](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)
- [Flushing before harvest: myth (summary)](https://genetixbay.com/knowledge/nutrients/flushing.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
3. Saloner A, Bernstein N. 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516