- Separate the air-gap and air-pump strategies and what each demands of you.
- Size starting water per plant from published lettuce allowances.
- Match method to power, season and crop length, then scale a proven unit.
01 / One root bath, two oxygen strategies
A Kratky vessel and an aerated deep water culture (DWC) vessel look alike; the difference is where oxygen comes from. CTAHR VC-1 describes the non-circulating method as a single initial application of water and nutrients with no electricity, pumps or aerators; as the level falls, roots between the net pot and the surface become “oxygen roots” in the humid air layer under the cover, while roots in the solution act as “water and nutrient roots”. VC-1 notes that oxygen in the solution falls progressively with depth, so the air space is the oxygen supply.
DWC holds the level high and pushes air into the water instead. Oregon State EM 9455 states that with minimal water movement and low air exchange, DWC requires effective aeration through air pumps and air stones or ozone injection. University of Minnesota Extension draws the same line: in a passive deep water system the air gap above the water provides the aeration, so roots should stay only one third to one half submerged once they grow beyond the net pot; where a single container is aerated, it names an airstone as the most common device.
Reading: A Suspended Net-Pot, Non-Circulating Hydroponic Method for Commercial Production of Leafy, Romaine, and Semi-Head Lettuce (VC-1) ↗ · Hydro hints: Deep water culture ↗ · Small-scale hydroponics ↗
02 / Water per plant on day one
Kratky stores the whole crop’s water before transplanting. VC-1 fills tanks with 1.5–2 US gallons of nutrient solution per plant and limits the method to crops needing less than 2 gallons per plant from transplant to harvest. UF/IFAS HS1488 gives a home allowance of 1–1.5 gallons per lettuce plant from seed to harvest; its worked example is a 5-gallon bucket filled until the water sits halfway up the net pots. Two published allowances in two climates, not a universal budget.
DWC sizes the vessel around root space and access, because you replace losses as you go. UMN’s rule is that any added water should carry nutrients at the label concentration, and its note that “set it and forget it” suits only short-lived crops such as lettuce harvested in 6–7 weeks applies to both methods. A Kratky vessel therefore stores more solution per plant at fill than a DWC vessel you top up.
Reading: A Suspended Net-Pot, Non-Circulating Hydroponic Method for Commercial Production of Leafy, Romaine, and Semi-Head Lettuce (VC-1) ↗ · “Set It and Forget It” Hydroponic Lettuce (HS1488) ↗ · Small-scale hydroponics ↗ · Hydro hints: Deep water culture ↗
03 / Temperature, oxygen and season
UF/IFAS HS1422 says the lettuce solution should stay between 65°F and 80°F with dissolved oxygen of 5 mg/L and EC between 1.2 and 1.8 mS/cm. VC-1 gives lettuce’s preferred growing temperature as 60–70°F, the air temperature of Hawai‘i’s upper elevations, and says lettuce tolerates the 80s and low 90s commonly met in rain shelters, at the cost of tip burn and bitter taste. Warm water holds less oxygen, and in a Kratky vessel you cannot add any, so the season is your oxygen control.
Heat also concentrates the solution. VC-1 reports growers adding solution at a lower EC (1.2–1.5 mS) in hot weather, when plants take up more water, and a higher EC (1.6–2.0 mS) in cool weather, around a starting point of 1.5 mS. In DWC the air pump keeps oxygen moving in warm weather, but the same drift shows as rising EC while the level falls.
Reading: Growing Lettuce in Small Hydroponic Systems (HS1422) ↗ · A Suspended Net-Pot, Non-Circulating Hydroponic Method for Commercial Production of Leafy, Romaine, and Semi-Head Lettuce (VC-1) ↗ · “Set It and Forget It” Hydroponic Lettuce (HS1488) ↗
04 / Crop length, labor and checks
Kratky trades daily attention for careful setup. VC-1 gives 4–6 weeks from transplant to harvest for leafy and semi-head lettuce, winter crops taking longer, and says the cover should not be lifted during the crop because roots tear. Consumption peaks late; VC-1’s remedy for a tank about to run dry is about ½–1 inch of water or half-strength solution, and deeper tanks if that recurs.
DWC trades the single fill for routine checks. EM 9455 stresses regular checks on pH, nutrient concentration and aeration equipment. In practice that is level, EC, pH, water temperature, the pump and the diffuser: small per day, never zero.
| Criterion | Kratky (non-circulating) | Aerated DWC |
|---|---|---|
| Oxygen source | Humid air space above a falling level (VC-1). | Air pump and diffuser (EM 9455). |
| Electricity | None (VC-1, HS1488). | Continuous air pump; GFCI/RCD and a drip loop are general practice. |
| Water at fill | 1.5–2 gal per plant (VC-1); 1–1.5 gal (HS1488). | Sized for root space; losses replaced with nutrient water (UMN). |
| Level | Never raise it once oxygen roots form (VC-1). | Hold near the fill line; UMN keeps about half the roots submerged. |
| Heat | Season is the oxygen control; 60–70°F growing temperature preferred (VC-1). | Air helps; solution 65–80°F, DO 5 mg/L (HS1422). |
| Main failure | Flooded air zone, running dry, rainfall (VC-1). | Air or power loss with roots in still water. |
Reading: A Suspended Net-Pot, Non-Circulating Hydroponic Method for Commercial Production of Leafy, Romaine, and Semi-Head Lettuce (VC-1) ↗ · “Set It and Forget It” Hydroponic Lettuce (HS1488) ↗ · Hydro hints: Deep water culture ↗ · Small-scale hydroponics ↗ · Growing Lettuce in Small Hydroponic Systems (HS1422) ↗
05 / What fails, and how fast
The Kratky failure is a level that goes the wrong way. VC-1 is explicit: the level may stay the same or fall but should not be raised, because submerging the oxygen roots will “drown” the plant, which is why it requires shelter from rainfall and recommends outdoor growing only in dry locations. The slower failure is too little water at fill, showing as a tank that empties before harvest.
The DWC failure is the pump. With the level held rather than falling, a stopped air pump leaves the submerged roots in still water with no falling level to grow oxygen roots into. None of the cited publications says how long lettuce roots tolerate that, so treat it as an outage to end quickly, not a number to plan around: keep a spare pump and diffuser and check air first when many plants wilt together.
Reading: A Suspended Net-Pot, Non-Circulating Hydroponic Method for Commercial Production of Leafy, Romaine, and Semi-Head Lettuce (VC-1) ↗ · Hydro hints: Deep water culture ↗
06 / Decide, then scale one unit at a time
Answer the questions below in order. Power, solution temperature in season and whether you need to open the lid usually settle it.
- Check power. No reliable outlet, or an outage that could go unnoticed for a day, points to Kratky.
- Check the season against the published ranges: VC-1’s 60–70°F preferred growing temperature and HS1422’s 65–80°F for the solution.
- Decide whether the lid opens. Repeated cuts or mixed plantings favor DWC; a whole-head harvest favors Kratky.
- Size the water. Kratky: plant count × a published allowance (HS1488 1–1.5 gal; VC-1 1.5–2 gal), filled so the solution reaches partway up the net pots (HS1488 halfway; VC-1 the lower ½ inch). DWC: root space, diffuser access and top-up water.
- Plan the failure. Kratky: rain shelter and a marked fill line. DWC: spare pump and diffuser.
- Run one crop, record remaining or top-up volume, peak water temperature and usable heads, then copy the unit.
FIELD QUESTIONYou have one 5-gallon bucket, no outlet nearby and a cool-season window of about six weeks. How many lettuce plants should the bucket carry as a Kratky vessel?
No power makes it Kratky. HS1488 allows 1–1.5 gallons per plant: 5 ÷ 1.5 ≈ 3.3 and 5 ÷ 1 = 5 plants. The bucket is filled only to halfway up the net pots, so usable volume is under 5 gallons; three plants sits at the cautious end of HS1488 (5 ÷ 3 ≈ 1.7 gallons each) and meets VC-1’s 1.5–2 gallons per plant only if the bucket really holds close to 5 gallons. Plant three and measure what is left at harvest.
Reading: A Suspended Net-Pot, Non-Circulating Hydroponic Method for Commercial Production of Leafy, Romaine, and Semi-Head Lettuce (VC-1) ↗ · “Set It and Forget It” Hydroponic Lettuce (HS1488) ↗ · Growing Lettuce in Small Hydroponic Systems (HS1422) ↗
Parts & buying criteria
Build your own parts & cost worksheet →
Showing aerated deep water culture. Quantities describe the teaching model. Specify real working volume, support, fittings and instruments for your installation.
01Nutrient reservoir1 · illustrated quantity+
Stores the measured nutrient solution beneath or beside the growing area.
Inspect: Compare the surface with the diffuser and the lower roots; freeboard is deliberate. There is no pump intake in this single-vessel example.
Maintain: Record level before refilling, keep light out and verify temperature, EC and pH.
Opaque, cleanable, intended-use container with volume marks and service access.
Check size, materials and operating conditions with your chosen supplier before ordering.02Lid & root support1 · illustrated quantity+
Holds the plant above the chamber or reservoir without pinching its crown.
Inspect: Separate the cover and inspect the basket or collar opening.
Maintain: Check fit as plants grow and keep unused openings covered.
Rigid compatible support with removable, correctly fitted baskets or collars.
Check size, materials and operating conditions with your chosen supplier before ordering.03Air pump & diffuser1 · illustrated quantity+
Delivers air below the water surface in this aerated DWC example.
Inspect: Trace the thin line from the dry pump to the diffuser. Bubbles are illustrative.
Maintain: Check actual delivery and dissolved oxygen; preserve backup air and prevent back-siphoning.
Rated output at the installed depth and diffuser resistance; accessible replaceable parts. Power it through ground-fault protection (GFCI/RCD) and keep the pump and its plug above the water line.
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 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.
- Oregon State University ExtensionHydro hints: Deep water culture ↗
Aerated water culture layout and operation.
- University of Minnesota ExtensionSmall-scale hydroponics ↗
Root support, transplanting, light, aeration and cleaning.
- 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 Florida IFAS ExtensionGrowing Lettuce in Small Hydroponic Systems (HS1422) ↗
Lettuce system choice and management.
The next useful connections.
Deep 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 →Growing methodsKratky: manage the water and the air gap
Grow a short-cycle crop without circulation, with enough starting solution and a fixed support that preserves the developing air zone.
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 →