# Ebb and flow

> Ebb and flow (flood and drain) periodically floods a tray of potted plants with nutrient solution, then drains it back to a reservoir, pulling fresh air into the medium.

- Canonical: https://genetixbay.com/knowledge/glossary/ebb-and-flow.html
- Also written: flood and drain, flood-and-drain, ebb & flow, ebb-and-flow, flood table, flood tray
- Glossary category: Systems and media · 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"

Ebb and flow is a [recirculating](https://genetixbay.com/knowledge/glossary/recirculating-system.md) hydroponic system. A timer-controlled pump fills a tray or bed with nutrient solution to a set depth, holds it briefly, and then lets it [drain](https://genetixbay.com/knowledge/glossary/runoff.md) back to the reservoir under gravity. As the solution drains, air is drawn into the medium, so roots get both water and oxygen each cycle.

## In practice

Plants sit in containers of [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md), [clay pebbles](https://genetixbay.com/knowledge/glossary/clay-pebbles.md) or [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) on a flood table. Floods typically last about 10-20 minutes, and the number per day rises from one or two for young plants to several in peak flower, depending on medium and [container size](https://genetixbay.com/knowledge/glossary/pot-size.md). An overflow fitting sets the maximum level and prevents spills if a timer fails. Reservoirs need to be large enough to flood the tray without running dry, and solution is changed regularly because returning runoff carries salts and root exudates.

## Don't confuse with

- **Drip irrigation**: delivers solution to each pot rather than flooding the whole tray.
- **Bottom watering**: a manual version of the same idea, without recirculation.

## Related terms

[Recirculating system](https://genetixbay.com/knowledge/glossary/recirculating-system.md), [Clay pebbles](https://genetixbay.com/knowledge/glossary/clay-pebbles.md), [Rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md), [Reservoir](https://genetixbay.com/knowledge/glossary/reservoir.md), [Wet-dry cycle](https://genetixbay.com/knowledge/glossary/wet-dry-cycle.md)

## Read more

- [Ebb and flow (flood and drain)](https://genetixbay.com/knowledge/systems/ebb-and-flow.md)

## Sources

1. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press. https://doi.org/10.1201/9781003133254