GenetixBayEST. 2009
Systems · Intermediate · 2 min read

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.

Supported
Draft: awaiting expert review Updated
VegFlowerDrip

Being reviewed. Our editors are double-checking a few figures in this article against primary sources. Marked passages may change.

Short answer. Drip emitters (typically 2–4 per plant, 2–8 L/h each) feed pots of coco, rockwool 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) being reviewed
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 scalebeing reviewed.
  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. Pre-harvest flushing is a Myth that costs you yield and resin: it starves the plant while it packs on its final weight, trichomes and resin. Feed through to harvest at stage strength. The only valid flush is a root-zone flush to clear salt build-up, at any stage (see the flush debate). 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.

Evidence

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

Questions this article answers

How many drip emitters per plant?

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.

Should I recirculate drip runoff?

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.

How often should I change a recirculating reservoir?

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.

What shot size for drip irrigation in coco?

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.

Sources

  1. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press (closed vs open systems). doi.org/10.1201/9781003133254
  2. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems (recirculation spreads pathogens). planttalk.colostate.edu/topics/miscellaneous/2043-root-disea
  3. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. doi.org/10.1016/C2015-0-01807-5
  4. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins)..

Related

Harvest and cureMythIntermediate · Draft

Pre-harvest flushing: a myth that costs you yield and resin

Pre-harvest flushing is a myth, and a harmful one. Starving the plant of nutrients in its last weeks takes food away during the phase when it is packing on most of its final weight, trichomes and resin, so it costs yield and resin and gives nothing back: controlled studies found no gain in flower quality, minerals or cannabinoids, and longer nutrient withdrawal tended to cut dry mass and cannabinoid yield. Cannabis stores what it takes up in its tissue, and plain water at the end does not wash it out. Feed through to harvest at stage-appropriate strength; taste and ash are made by plant health, not overfeeding, and slow drying and proper curing. The one valid flush treats the medium, not the plant: a root-zone flush to wash out accumulated salts, at any stage.

Grower practiceAdvanced · Draft

Drain-to-waste drip and crop steering (generative vs vegetative dryback)

Drain-to-waste drip sends fresh solution every shot and discards runoff, so you control the root zone by irrigation timing, shot size and substrate EC measured with a VWC/EC probe. Vegetative steering uses earlier first shots, larger shots and small overnight drybacks (about 10–15 % VWC); generative steering delays the first shot, uses smaller shots, longer P3 and larger drybacks (about 20–35 %) with higher substrate EC. The ranges are grower practice; one cannabis study found controlled late-flower drought raised cannabinoid concentration.

SupportedIntermediate · Draft

Growing in coco coir

Coco coir is a hydroponic substrate that looks like soil: inert-ish, airy, and fed every irrigation with a complete mineral solution at pH 5.8–6.2 and EC 1.2–2.4 mS/cm with 10–20 % runoff. Use pre-washed, buffered coco or buffer it yourself with a calcium/magnesium solution, because raw coir holds potassium and sodium and grabs calcium and magnesium.

SupportedAdvanced · Draft

Growing in rockwool (stonewool cubes and slabs)

Rockwool is an inert, unbuffered mineral fibre that holds a lot of water and air and gives precise control over the root zone. Pre-soak at pH about 5.5, run pH 5.5–6.0 and EC 1.8–3.0 mS/cm in flower, and manage it by volumetric water content and slab EC. It is the native medium of crop steering, and it punishes neglect quickly because nothing buffers mistakes.

SupportedIntermediate · Draft

Ebb and flow (flood and drain)

A pump floods a table or tray of pots to a standpipe height, then the solution drains back to the reservoir. Each flood refreshes water and pulls fresh air into the medium as it drains. Typical schedules: clay pebbles 3–6 floods per light period of 10–15 minutes, coco or rockwool 1–3. It is robust because the media buffer pump failures for days, but salts can build up at the top of the medium.

Grower practiceBeginner · Draft

Choosing your growing system: soil, coco, rockwool or hydro

Choose by how much attention and measurement you can give, not by yield claims. Soil and living soil forgive mistakes for days; coco and drip need daily feeding; DWC, NFT and aeroponics grow fast but can lose roots within hours if a pump or air supply fails. No controlled study shows one system out-yielding the others when light and climate are equal.

Was this helpful?

Tell us by joining the waitlist: Founding Members shape what the Professor writes next.

Yes, keep them comingNot quite: I want more
Professor Greenleaf

Grow with the Professor.

The GenetixBay community is coming: honest grow journals, permanent GB-IDs for genetics, and a Professor who answers with citations. Founding Members get first access and the lowest numbers in the archive.

Join the waitlistFund the Bay