- Explain why the water inventory around the roots decides the rest.
- Predict what each system does when the pump or the power stops.
- Match method to floor, temperature swing, harvest workflow and cleaning time.
01 / Two ways to wet a root
Both are water culture: roots meet solution directly, with no bed of medium. Oregon State EM 9457 describes NFT as a thin, continuous film flowing along a channel; EM 9455 describes DWC as roots submerged in solution kept oxygenated by air pumps and stones. The deciding difference is how much water surrounds the roots and whether it moves.
In NFT that water is shallow and moving; Oklahoma State HLA-6442 notes that constant flow means the pump needs no timer, while UF/IFAS HS1422 says an irrigation timer may be needed for NFT because too much water can cause root rot there. In DWC it is deep and nearly still, which is why EM 9455 says effective aeration is required. University of Minnesota Extension calls DWC the most common small-scale system and the easiest to expand. Both OSU publications list lettuce, spinach, kale and the same four herbs, so crop choice will not settle this; site, supervision, floor and cleaning will.
| Criterion | NFT | DWC |
|---|---|---|
| Water at the root | Thin moving film in a sloped channel (EM 9457) | Still, aerated bath (EM 9455) |
| Pump role | Continuous circulation, no timer (HLA-6442) | Air pump and stones (EM 9455) |
| Power stops | Immediate wilting possible (EM 9457) | Aeration stops; water remains (original reading) |
| Temperature | Follows ambient swings (EM 9457) | Large volume buffers change (EM 9455) |
| Root space | Limited; small-rooted crops (EM 9457) | Roots hang freely, about half submerged (UMN) |
| Weight and scaling | Separate tank; vertical levels add shading (EM 9457) | On the ground; several tanks localise leaks (EM 9455) |
| Emptying | Channels, emitters and lines; clogs (EM 9457) | Bottom bulkhead and valve (EM 9455) |
Reading: Hydro hints: Nutrient film technique ↗ · Hydro hints: Deep water culture ↗ · Hydroponics (HLA-6442) ↗ · Small-scale hydroponics ↗ · Growing Lettuce in Small Hydroponic Systems (HS1422) ↗
02 / What a stopped pump does
EM 9457 states that power loss or pump failure can lead to immediate plant wilting because the film ceases, and calls backups for power and pumps crucial. UMN says pump-dependent systems leave plants unable to reach water after an outage, so they dry out quickly, and that the generators larger growers use are less practical at small scale. UMN also warns that a reservoir falling below the pump can damage it.
A DWC tank does not remove the dependency; it changes what fails first. When the air pump stops, oxygen delivery stops, but the roots stay in solution. No cited publication puts a number on how long a leafy crop tolerates an unaerated bath, and this guide does not either: the stored water is time to respond, not permission to leave the system unattended. How long would a stopped pump go unnoticed at your site? A weekend argues for DWC or a tested NFT backup; minutes narrow the gap.
Reading: Hydro hints: Nutrient film technique ↗ · Small-scale hydroponics ↗
03 / Temperature and oxygen in the root zone
EM 9457 says NFT’s shallow channels are sensitive to ambient temperature changes, which can cause nutrient imbalances and plant stress, and names three mitigations: increase slope, shorten channels and use larger stock tanks. EM 9455 makes the opposite observation for DWC: the large water volume acts as a thermal buffer against day–night and weather fluctuations.
UF/IFAS HS1422 says lettuce solution should stay between 65°F and 80°F with good oxygenation, printing a dissolved-oxygen figure of 5 mg/L; those are that publication’s lettuce figures, not targets for every herb. On oxygen, EM 9457 credits the moving film with a consistent supply of nutrients and oxygen, while EM 9455 says DWC aeration must be built in and UMN keeps roots touching but not fully immersed. Read temperature and dissolved oxygen at the root, not from the pump label.
Reading: Hydro hints: Nutrient film technique ↗ · Hydro hints: Deep water culture ↗ · Growing Lettuce in Small Hydroponic Systems (HS1422) ↗ · Small-scale hydroponics ↗
04 / Footprint, spacing and harvest
EM 9457 notes that storing most of the solution in a separate tank lets NFT fit rooftops or façades without exceeding structural limits, and that vertical stacking adds shading with each level. EM 9455 says DWC uses large volumes of water that should be supported on the ground, levelled within one inch. An upstairs room therefore argues for NFT; a slab is indifferent.
EM 9455 describes conveyor-belt production: transplants start at one end of the tank and rafts are pushed toward the other as plants grow. NFT is replanted channel by channel. HS1422 says short-term crops of 50–60 days such as lettuce suit a wide range of systems, while crops beyond 60 days are harder in NFT or floating-bed systems. EM 9455 and UMN both warn against letting solution drip from lifted roots onto growing plants.
Reading: Hydro hints: Nutrient film technique ↗ · Hydro hints: Deep water culture ↗ · Small-scale hydroponics ↗ · Growing Lettuce in Small Hydroponic Systems (HS1422) ↗
05 / Cleaning and turnover between crops
UMN’s between-plantings routine for a container is to drain, wash with detergent and a brush, rinse with potable water, then sanitise, with one household example of 1 tablespoon of bleach per gallon, roughly 150–200 ppm, left to air dry. Its NFT section changes the last step: the same 150–200 ppm bleach solution is run through the reservoir and lines for up to 3 hours and then flushed with a 2–3 hour rinse cycle of municipal water. An NFT unit has channels, emitters, supply and drain lines, and EM 9457 asks for regular monitoring to prevent clogs. A DWC tank has walls, a raft or lid and an air line, and EM 9455 recommends a bottom bulkhead fitting and valve for draining.
Turnover is another point where the sources differ. UMN’s NFT maintenance list says change the reservoir after every crop cycle, while its answer on how often to change the solution says fast-maturing leafy greens rarely need a change-out; decide with your own EC and pH records. EM 9455 adds two DWC measures against algae: cover the water surface with opaque material and size rafts to the tank so gaps are minimal. One tank is one vessel to scrub; six channels and their fittings are not.
Reading: Small-scale hydroponics ↗ · Hydro hints: Nutrient film technique ↗ · Hydro hints: Deep water culture ↗
06 / Decide for your site
These steps are original guidance and do not rank one method as better; a grower with a concrete floor and constant supervision and one with an upstairs room who travels can reasonably choose differently. The exercise shows what a catalogue photograph hides: where the reservoir sits and what the floor carries.
- Write down the crop and its cycle. HS1422’s 50–60 day lettuce fits either; anything kept beyond 60 days argues against both.
- Estimate how long a stopped pump would go unnoticed; hours or days call for a tested NFT backup, as EM 9457 advises, or for a DWC bath.
- Check the floor and the room’s daily temperature swing. An upper floor favours EM 9457’s separate-tank NFT; a ground slab and a large swing favour a tank’s buffering volume.
- Choose the harvest workflow and count the surfaces, lines and fittings you will wash, rinse and sanitise by UMN’s routine.
- Build one unit, run it with water only, switch the pump off and watch, then record root-zone temperature and dissolved oxygen before planting.
FIELD QUESTIONYou have a 1.5 m × 1.5 m corner on an upper floor and want about 36 lettuce positions. What does UMN’s table-top NFT example tell you, and what must you check before choosing a DWC tank instead?
UMN’s example is six 4-foot channels in a 55 × 55 × 31 inch unit holding 36 plants. 55 in × 2.54 = 139.7 cm, so the table takes about 1.4 m each way and leaves roughly 5 cm a side. UMN lists a reservoir among the required parts and does not say whether that footprint includes it, so allow space for one. Footprint: 55 × 55 = 3,025 in² ÷ 144 = 21.0 ft², so 36 ÷ 21 ≈ 1.7 positions per square foot in that one layout, not a design density. For a DWC tank, EM 9455 wants it on the ground and level within one inch, so resolve the upper floor first; the position count then depends on the raft spacing you choose.
Reading: Small-scale hydroponics ↗ · Hydro hints: Deep water culture ↗ · Growing Lettuce in Small Hydroponic Systems (HS1422) ↗ · Hydro hints: Nutrient film technique ↗
Parts & buying criteria
Build your own parts & cost worksheet →
Showing nutrient film technique. Quantities describe the teaching model. Specify real working volume, support, fittings and instruments for your installation.
01Reservoir1 · illustrated quantity+
Holds the recirculating nutrient solution. This is the common sampling and refill point for both channels.
Inspect: In cutaway view, compare the water surface with the pump intake. The drawing leaves room above the water; it does not specify a working volume.
Maintain: Record the level before adding water. Inspect the cover, clean accessible deposits and keep the intake submerged during use.
Opaque, cleanable container rated by its manufacturer for the intended use; accessible lid and drain.
Check size, materials and operating conditions with your chosen supplier before ordering.02Pump & supply1 · illustrated quantity+
Lifts solution from the reservoir to the channel inlets. Cyan packets indicate the direction of delivery.
Inspect: Follow the rising supply pipe and its branch to each channel. Both inlets need an observable supply.
Maintain: Disconnect power before opening the pump. Inspect its inlet screen and confirm both branches flow after reassembly.
Compare the pump curve at the installed lift and pipe resistance; include service access and replacement availability. Supply the pump, timer and any air pump through ground-fault protection (GFCI/RCD), keep plugs and cord connections above the water line with a drip loop, and switch off and unplug before reaching into the solution.
Check size, materials and operating conditions with your chosen supplier before ordering.03Growing channels1 · illustrated quantity+
Contain the shallow stream beneath the plants and guide it toward the return.
Inspect: Open the cutaway to find the channel floor beneath the roots. The slope is exaggerated for reading.
Maintain: Look along each channel for ponding, debris or an obstructing root mat; inspect the outlet before changing the pump.
Removable covers, supported slope, smooth cleanable surfaces and outlets accessible with plants in place.
Check size, materials and operating conditions with your chosen supplier before ordering.04Plant baskets6 illustrated · illustrated quantity+
Bridge the opening in the channel cover while allowing roots to pass through.
Inspect: In exploded view, the baskets lift above the channels. The open slats reveal the relationship between support and roots.
Maintain: Check that each rim sits securely and that roots are not pinched at transplanting or inspection.
Match the basket rim and hole diameter; allow removal without damaging adjacent plants.
Check size, materials and operating conditions with your chosen supplier before ordering.05Support mediumFor 6 baskets · illustrated quantity+
The illustrated expanded clay supports the seedling in its basket. The channels are not filled with aggregate.
Inspect: Select the brown pebbles and separate the basket in exploded view. Media texture is simplified.
Maintain: Remove loose particles before installation. Inspect whether the starter plug stays appropriately moist.
Select a stable grade that stays in the basket; compare water retention, dust and cleaning requirements.
Check size, materials and operating conditions with your chosen supplier before ordering.06Gravity return1 · illustrated quantity+
Collects channel outflow and brings it back to the reservoir without a second pump.
Inspect: Trace the low ends of both channels into the common return. Inspect the full path before assuming the circuit is clear.
Maintain: Remove obstructions and check for leaks. Test drainage with the pump off during commissioning.
Removable unions, supported pipe and sufficient drain capacity under the actual installation conditions.
Check size, materials and operating conditions with your chosen supplier before ordering.Evidence beside the lesson.
Source checks: September 2026. The geometry, inspection exercises and worksheets are original teaching material. The named organizations have not endorsed or reviewed this site.
Published recipe rates and planning ranges retain their source context. Calculator equations are accounting tools; they do not predict uptake, yield, toxicity or safe stocking. Model dimensions, water speeds, roots and fish counts are illustrative. Verify species, crop, source water and product labels for a real system.
- Oregon State University ExtensionHydro hints: Nutrient film technique ↗
Channel slope, root space and flow continuity.
- Oregon State University ExtensionHydro hints: Deep water culture ↗
Aerated water culture layout and operation.
- Oklahoma State University ExtensionHydroponics (HLA-6442) ↗
System categories and recirculating nutrient delivery.
- University of Minnesota ExtensionSmall-scale hydroponics ↗
Root support, transplanting, light, aeration and cleaning.
- University of Florida IFAS ExtensionGrowing Lettuce in Small Hydroponic Systems (HS1422) ↗
Lettuce system choice and management.
The next useful connections.
From reservoir to roots.
Follow a nutrient film system from its first inlet to its last root. Learn what each part does, what to inspect, and how the pieces work together.
12 min + model exploration →Growing methodsDeep water culture: build an aerated root bath
A complete single-vessel DWC workflow, from water level and air delivery to nutrient management and harvest.
6 min + guided practice →Crops & environmentLeafy greens and herbs: plan a repeatable crop
Choose a first crop, manage spacing and harvest timing, and avoid forcing every herb into lettuce conditions.
6 min + guided practice →ComparisonsKratky vs DWC for lettuce: pick by power, season and scale
Both methods hang lettuce roots in stored nutrient solution; they differ in where oxygen comes from, how much water each plant needs on day one and what fails first.
7 min + guided practice →