# Bottom watering

> Bottom watering lets a pot absorb water or solution from a tray beneath it, so the medium wets from the base upward by capillary action.

- Canonical: https://genetixbay.com/knowledge/glossary/bottom-watering.html
- Also written: bottom-watering, bottom feeding, sub-irrigation, subirrigation, watering from below, tray watering
- 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"

Bottom watering (sub-irrigation) means standing a container in a shallow tray of water or nutrient solution and letting it soak up through the [drainage](https://genetixbay.com/knowledge/glossary/runoff.md) holes. Water moves upward by capillarity until the medium is moist, and the excess is then removed. [Ebb-and-flow](https://genetixbay.com/knowledge/glossary/ebb-and-flow.md) tables automate the same process.

## In practice

It wets dry [peat](https://genetixbay.com/knowledge/glossary/peat.md) and [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) that repel water from above, keeps the surface drier (which discourages [fungus gnats](https://genetixbay.com/knowledge/glossary/fungus-gnat.md)), and avoids splashing. Leave the pot in the tray for about 15-30 minutes, then empty what remains; leaving a pot standing in water for hours waterlogs the base. Because water moves only upward and does not drain through, salts build up near the surface over time, so top-water to runoff now and then to clear them.

Commercial nurseries use sub-irrigation widely for potted plants.

## Don't confuse with

- **Wick system**: continuous capillary feed through a cord.
- **Ebb and flow**: automated, [recirculating](https://genetixbay.com/knowledge/glossary/recirculating-system.md) flood-and-drain.

## Related terms

[Wick system](https://genetixbay.com/knowledge/glossary/wick-system.md), [Ebb and flow](https://genetixbay.com/knowledge/glossary/ebb-and-flow.md), [Overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md), [Ceramic sensor watering](https://genetixbay.com/knowledge/glossary/ceramic-sensor-watering.md)

## Read more

- [Bottom-watering, soak trays and wick (self-watering) systems](https://genetixbay.com/knowledge/systems/bottom-watering-wick.md)

## Sources

1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5