# Recirculating drip (top-feed, runoff returns)

> A pump pushes nutrient solution through drip emitters into pots of coco, rockwool or clay pebbles and the runoff returns to the reservoir. It saves water and nutrients but the reservoir slowly drifts as runoff brings back salts and root exudates, so monitor runoff and refresh when reservoir chemistry diverges. Typical shots are 2–6 % of pot volume, first shot 1–2 h after lights-on, none in the dark.

- Canonical: https://genetixbay.com/knowledge/systems/recirculating-drip.html
- Category: Systems · Level: Intermediate
- Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked)
- Stage: Veg, Flower · Systems: Drip
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Questions and answers

**How many drip emitters per plant?** Most cannabis drip setups use 2–4 emitters per plant, each delivering about 2–8 litres per hour, spread around the pot so the medium wets evenly. Use pressure-compensating emitters on long lines and a filter of at least 120 mesh before the manifold. Calibrate weekly by collecting one emitter's output for one minute, since a clogged emitter can leave one plant dry.

**Should I recirculate drip [runoff](https://genetixbay.com/knowledge/glossary/runoff.md)?** Recirculating drip runoff saves water and fertiliser, but it comes with two costs. The reservoir drifts as plants take up ions unevenly and runoff returns salts and root exudates, and recirculation spreads any root pathogen to every plant. Recirculate only if you will monitor runoff and reservoir EC, refresh on schedule, and never return runoff from a diseased plant.

**How often should I change a recirculating reservoir?** Change a recirculating drip reservoir every 7–14 days, or sooner when runoff and input [EC](https://genetixbay.com/knowledge/glossary/ec.md) diverge by more than about 0.5 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md). Rising reservoir EC with a steady feed is another refresh trigger. Between changes, top off with plain water or weak feed, and remember 'it's recirculating, it's fine' is a common mistake that lets chemistry drift.

**What shot size for drip irrigation in [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md)?** Drip shots in coco typically run about 2–6% of the [pot volume](https://genetixbay.com/knowledge/glossary/pot-size.md) per shot in veg, a grower starting point to verify for your setup. Give the first shot 1–2 hours after lights-on and the last 2–4 hours before lights-off, with no shots in the dark by default. Aim for 10–30% runoff overall and keep coco input [pH](https://genetixbay.com/knowledge/glossary/ph.md) at 5.8–6.2.

**Short answer.** Drip emitters (typically **2–4 per plant, 2–8 L/h each**) feed pots of coco, [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) or clay; runoff drains back to the reservoir [4]. You reuse water and fertiliser, but the reservoir drifts: plants take up ions unevenly and runoff returns salts and exudates. Watch reservoir vs runoff EC and **refresh when they diverge by more than ~0.5 mS/cm** (Jardin rule) [4]. Recirculation also spreads root pathogens to every plant [2].

## Numbers that matter

| Parameter | Target | Notes |
|---|---|---|
| Emitters | 2–4 per plant, 2–8 L/h | Spread around the pot to wet it evenly |
| Shot size | 2–6 % of pot volume per shot (veg) | |
| First shot | 1–2 h after lights-on | |
| Last shot | 2–4 h before lights-off | |
| Night shots | None by default | |
| Runoff | 10–30 % of applied, returned | |
| Refresh trigger | Runoff/input EC divergence > 0.5 mS/cm, or every 7–14 days | [4] |
| pH / EC | Per medium (coco 5.8–6.2, rockwool 5.5–6.0) | |

## How to run it

1. Size the pump for all emitters at pressure; use pressure-compensating emitters on long lines.
2. Filter (≥ 120 mesh) before the manifold; emitters clog.
3. Calibrate: collect one emitter for 1 minute and confirm flow; repeat weekly.
4. Return runoff through a screen; consider UV or slow-sand filtration at commercial scale.
5. Top off with plain water or weak feed; full refresh on trigger.

## Failure modes

| Problem | Sign | Jardin response [4] |
|---|---|---|
| Emitter clog | One plant dry, shot volume low | Raise shot time up to +50 %; alert at −40 % |
| Line split | Shot volume high, reservoir mass drops without return | Close zone |
| Runoff tray overflow | Float trips | Pump off |
| Pump dead | No current | Alert; media buy 12–36 h |
| Reservoir EC creeping | Rising EC with steady feed | Refresh |

## Jardin notes

Jardin method "Drip, recirculating": flow meter per manifold, reservoir mass, runoff tray float required; one VWC probe per zone turns it into a steered system. Time-to-harm 12–36 h. Automation level 3 [4].

## Common mistakes

- **[Flushing before harvest](https://genetixbay.com/knowledge/glossary/flushing.md).** Pre-harvest flushing is a *Myth* that costs you yield and resin: it starves the plant while it packs on its final weight, [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) and resin. Feed through to harvest at stage strength. The only valid flush is a [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) to clear [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md), at any stage (see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)). In recirculating systems the reset is a fresh reservoir plus a light-solution flush of the pots.
- No filter → clogged emitters → one dead plant.
- Never refreshing ("it's recirculating, it's fine").
- Recirculating from a plant with [root disease](https://genetixbay.com/knowledge/glossary/root-rot.md).

## Evidence

Closed-system drift and pathogen spread are *Established* hydroponic knowledge [1][2][3]. Cannabis-specific shot sizes and timing are *Grower practice*.

## Sources

1. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press (closed vs open systems). https://doi.org/10.1201/9781003133254
2. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems (recirculation spreads pathogens). https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/
3. 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
4. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins).