- Turn lid thickness, channel width and plug size into pot diameter, depth and hole-saw size.
- Choose between net pots, foam collars and slit collars by crop, harvest and cleaning.
- Lay out positions from published lettuce spacing and count pots per channel or raft.
01 / Start from the opening, not the pot
University of Minnesota Extension defines the part: a pot with holes or slits in its sides so roots reach the solution below, sold in a variety of sizes. Which size you need is fixed by the lid or channel, the plug and the plant. Oregon State EM 9457 says NFT channels offer limited rooting space and suit short-lived or small-rooted crops such as herbs and leafy greens; its drawing rests the plant in a plug of growing media above the channel bottom.
SRAC 5007 adds that seedlings sit in holes in the channel, on the bottom or slightly raised, and that hole size depends on whether cubes or net pots are used. The first line of the specification is that choice; diameter follows.
Reading: Small-scale hydroponics ↗ · Hydro hints: Nutrient film technique ↗ · Principles of Small-Scale Aquaponics (SRAC 5007) ↗
02 / Diameter, hole saw and sheet thickness
SRAC 454 says two-inch net pots are generally used for leafy greens and 3-inch pots for larger plants such as tomatoes or okra, that holes of the same size are cut in the polystyrene, and that the lip keeps the pot from falling through. UF/IFAS HS1488 and CTAHR VC-1 both use a 2-inch hole saw for 2-inch pots; VC-1 cuts three-quarters through from one side and finishes from the other so the plug does not stick.
Sheet thickness changes the answer because pots taper. UF/IFAS HS943 calls for a 1¾-inch saw for 2-inch pots in 1½-inch Styrofoam and a 2½-inch saw for 3-inch pots, and says a thicker sheet needs a larger hole. Nominal sizes are lip diameters, so measure a sample at the lip and at sheet depth and test one hole in scrap; UMN’s rule is that the hole passes most of the pot and the lip rests on top. In channels the limit is width: SRAC 454’s NFT troughs are 4 to 6 inches wide.
Reading: Aquaponics—Integrating Fish and Plant Culture (SRAC 454) ↗ · “Set It and Forget It” Hydroponic Lettuce (HS1488) ↗ · A Suspended Net-Pot, Non-Circulating Hydroponic Method for Commercial Production of Leafy, Romaine, and Semi-Head Lettuce (VC-1) ↗ · Building a Floating Hydroponic Garden (HS943) ↗ · Small-scale hydroponics ↗
03 / Net pot, foam collar or slit collar
The cited documents cover net pots and drilled holes; this comparison is original. A net pot holds a plug or loose medium, carries a heavy head and keeps media out of the channel, but roots lock into it. VC-1 describes the cost: after harvest the pots are cleared of roots, debris and medium, soaked in a 10-percent bleach solution, rinsed and dried.
A foam collar grips the stem, not a root ball: roots go straight to the water and there is little to scrub, but a top-heavy plant leans and a plug-raised seedling has nowhere to sit. A slit collar is cut to the centre so a plant is fitted or removed without threading roots through a hole; HS943 accepts a Styrofoam coffee cup with slits cut in the bottom in place of a net pot. UMN’s cleaning list includes net pots and polystyrene boards; count what you will wash.
Reading: A Suspended Net-Pot, Non-Circulating Hydroponic Method for Commercial Production of Leafy, Romaine, and Semi-Head Lettuce (VC-1) ↗ · Building a Floating Hydroponic Garden (HS943) ↗ · Small-scale hydroponics ↗
04 / Pot depth, plug size and the water line
VC-1 places 1–3-week-old seedlings in net pots with medium or grow-plugs, immerses the lower ½–1 inch of each pot so the medium wets by capillary action, and accepts a plug that does not fill the pot. HS943 keeps cups no more than 1/16 inch below the sheet so the root ball wicks without drowning, and packs nothing around it. HS1488 fills its bucket halfway up the net cups; SRAC 454’s raft pots just touch the water.
Those figures belong to a still tank, a floating sheet, a bucket and a raft channel and are not interchangeable; the shared rule is that the plug, not the pot, makes the moisture connection. UMN says cubes are ready when roots have pushed through the bottom and that the pot should be only partially submerged so roots get oxygen. Measure the plug, then buy a pot whose inside depth keeps the plug top below the lip and whose base reaches your water line.
Reading: A Suspended Net-Pot, Non-Circulating Hydroponic Method for Commercial Production of Leafy, Romaine, and Semi-Head Lettuce (VC-1) ↗ · Building a Floating Hydroponic Garden (HS943) ↗ · “Set It and Forget It” Hydroponic Lettuce (HS1488) ↗ · Aquaponics—Integrating Fish and Plant Culture (SRAC 454) ↗ · Small-scale hydroponics ↗
05 / Materials, sunlight and service life
VC-1 prefers ½–1-inch expanded polystyrene of 2 lb/ft³ density or extruded polystyrene because holes cut easily, handles it as 2 × 4 ft pieces because 4 × 8 ft sheets are often broken in handling, says white latex paint on the polystyrene prolongs its life and warns that dark-coloured plastic or plywood covers heat up in direct sunlight. HS943 uses 1½-inch sheet; HS1422’s raft list has a 2-inch Styrofoam surface; UMN rests a board on PVC tubes slightly above the water.
For the pots the cited sheets give no material or lifetime figures, so this is original buying advice: ask whether the plastic is UV-stabilised and food-contact grade, buy one mould so every pot tapers alike, expect outdoor pots to go brittle first, and retire a pot when its lip cracks.
Reading: A Suspended Net-Pot, Non-Circulating Hydroponic Method for Commercial Production of Leafy, Romaine, and Semi-Head Lettuce (VC-1) ↗ · Building a Floating Hydroponic Garden (HS943) ↗ · Growing Lettuce in Small Hydroponic Systems (HS1422) ↗ · Small-scale hydroponics ↗
06 / Spacing as published, then the spec sheet
Each published figure is tied to a crop and system. SRAC 454’s UVI raft design grows green leaf lettuce at 48 plants per 8 × 4 ft sheet, 16 per square metre, on a four-week cycle, cultures Bibb transplants for three weeks at 29.3 per square metre, and sets NFT density by the distance between troughs. VC-1 names two common lettuce densities, 1.5 and 1.9 plants per square foot, 48 and 60 per 4 × 8 ft tank, warns that over two per square foot crowds large head cultivars grown to maturity, and asks for a small trial first; its 1.5 layout puts three staggered rows 8 inches apart with plants 12 inches apart along each row. HS943 suggests 6 inches from the sides and 12 inches apart, 32 holes per 4 × 8 ft sheet. UMN’s home advice is to follow the seed packet.
Fill the middle column from your measurements, then ask each supplier for the same items.
- Fix the crop and harvest stage; whole heads take the lower published densities.
- Measure sheet thickness, flat lid width and usable length.
- Choose the support type and measure your plug.
- Measure lip and body on a sample pot; test-cut one hole in scrap.
- Lay out centres from a published layout and count positions.
- Specify material and one mould; order a pot per position plus spares.
- After the first crop, record crowding, lean and root lock, then revise.
| Criterion | What to write down | Where the figure comes from |
|---|---|---|
| Support type | Net pot, collar or slotted cup, per crop | Original comparison; HS943; SRAC 5007 |
| Pot diameter | Lip and body at sheet depth | SRAC 454: 2-inch greens, 3-inch tomato and okra |
| Hole saw | Saw size; test cut on scrap | HS943 1¾ inch for 2-inch pots in 1½-inch sheet; VC-1, HS1488 2-inch |
| Lid or channel | Sheet thickness; flat lid width | SRAC 454 troughs 4–6 inches; VC-1 ½–1 inch, HS943 1½ inch, HS1422 2 inch |
| Depth and plug | Plug height; inside depth; immersion | VC-1 ½–1 inch; HS943 at most 1/16 inch below sheet; HS1488 halfway; SRAC 454 touching |
| Material | UV stabilisation, food contact, one mould | Original; VC-1 white paint |
| Spacing | Centres and count, with crop | SRAC 454 48 per sheet; VC-1 1.5–1.9/ft²; HS943 12 inches |
| Cleaning and spares | Pots plus spares; wash routine | UMN; VC-1 bleach soak |
FIELD QUESTIONFour 8-foot NFT channels with 4-inch lids and one 4 × 8 ft raft, all green leaf lettuce to whole heads. How many 2-inch net pots?
Channels: borrowing the 12-inch in-row spacing from VC-1’s 1.5 per square foot tank layout (a raft figure, not an NFT one), 96 ÷ 12 = 8 per 8-foot channel and 32 for four; SRAC 454 says the distance between troughs then sets density. Raft: 4 × 8 = 32 ft². VC-1’s 1.5 gives 32 × 1.5 = 48, matching SRAC 454’s 48 per sheet. VC-1’s 1.9 gives 32 × 1.9 ≈ 61, laid out as 60; HS943’s 12-inch grid gives 32. Whole heads argue for 48. Total 32 + 48 = 80 pots; order about 90 for breakage. These are published lettuce layouts, not a rule for your cultivar.
Reading: Aquaponics—Integrating Fish and Plant Culture (SRAC 454) ↗ · A Suspended Net-Pot, Non-Circulating Hydroponic Method for Commercial Production of Leafy, Romaine, and Semi-Head Lettuce (VC-1) ↗ · Building a Floating Hydroponic Garden (HS943) ↗ · Small-scale hydroponics ↗
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.
- University of Minnesota ExtensionSmall-scale hydroponics ↗
Root support, transplanting, light, aeration and cleaning.
- Oregon State University ExtensionHydro hints: Nutrient film technique ↗
Channel slope, root space and flow continuity.
- Southern Regional Aquaculture Center · hosted by OSU ExtensionPrinciples of Small-Scale Aquaponics (SRAC 5007) ↗
Design, media-bed depth, biofilter sizing and aeration, potassium/calcium/iron supplementation and the UVI feed-to-area rule restated in ounces per square foot; applicability depends on system.
- Southern Regional Aquaculture Center · hosted by OSU ExtensionAquaponics—Integrating Fish and Plant Culture (SRAC 454) ↗
Tank-to-treatment-to-growing-to-sump layout and production tradeoffs.
- University of Florida IFAS Extension“Set It and Forget It” Hydroponic Lettuce (HS1488) ↗
A small non-circulating lettuce example; seasonal and product assumptions apply.
- University of Hawai‘i at Mānoa, CTAHR (B. A. Kratky)A Suspended Net-Pot, Non-Circulating Hydroponic Method for Commercial Production of Leafy, Romaine, and Semi-Head Lettuce (VC-1) ↗
Originating description of the suspended net-pot method: single initial fill, falling level and the expanding moist air space in which upper roots develop; tank covers of ½–1-inch expanded (2 lb/ft³) or extruded polystyrene handled as 2 × 4 ft pieces and painted white; 2-inch hole-saw technique; lettuce densities of 1.5 and 1.9 plants/ft² (48 and 60 per 4 × 8 ft tank) with staggered layouts; 1–3-week-old seedlings with the lower ½–1 inch of the net pot immersed; 10-percent bleach soak of net pots after harvest.
- University of Florida IFAS ExtensionBuilding a Floating Hydroponic Garden (HS943) ↗
The 4 × 8 ft floating garden build: 1½-inch Styrofoam sheet; a 1¾-inch hole saw for 2-inch net pots and a 2½-inch hole saw for 3-inch net pots or slotted Styrofoam cups, with a larger hole needed in thicker sheet; cup bottoms level with the underside of the sheet and not more than 1/16 inch below it; the transplant root ball sitting alone in the cup with no added media; a suggested spacing of 6 inches from the sides and 12 inches apart giving 32 holes; a minimum 5 inches of solution.
- 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 →System designsFish. Filters. Roots.
Explore the living system between a fish tank and a growing bed. Separate water movement from waste handling, biological filtration, and the needs of the plants.
14 min + model exploration →Media & propagationFrom seed to a working root system
Start consistent seedlings, establish root contact and transplant without importing avoidable problems.
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 →ComparisonsNFT or DWC for leafy greens: flowing film or still bath
Compare a sloped channel carrying a thin film with an aerated tank of standing solution: outage behaviour, root temperature and oxygen, footprint, harvest and cleaning.
8 min + guided practice →