- Distinguish a fixed support from a floating raft.
- Budget starting water for a short-cycle crop.
- Preserve root access to both solution and humid air.
01 / Why the falling level matters
A non-circulating system stores its nutrient solution under a fixed plant support. As the level falls, an upper humid air zone develops while lower roots remain in solution. The illustrated uptake path represents water moving into the plant; it is not a pumped loop.
A fixed lid must not be confused with a floating raft that follows the water down. The method depends on how the upper and lower roots access air and water. Treat topping up as a design decision: refilling to the original high level can submerge roots that developed in the air zone.
Reading: “Set It and Forget It” Hydroponic Lettuce (HS1488) ↗
02 / Prepare a complete crop vessel
Choose a small leafy crop and a season in which the solution will stay suitable for it. Size the initial solution for the expected whole crop, including evaporation. UF/IFAS gives 1–1.5 US gallons per lettuce plant for its small-system example, approximately 3.8–5.7 L. This is a source-specific starting allowance, not a guaranteed water budget for every climate or cultivar.
Use an opaque vessel, secure lid, supported net pot, contained plug and a means of inspecting solution level without lifting the entire crop. Keep rain and debris out while retaining the root zone’s intended access to air.
- Mark an initial fill level that brings moisture to the seedling’s existing roots or bottom of the plug. Keep the crown above the solution.
- Prepare a complete hydroponic nutrient solution to final volume. Record the water source, product rate, EC and pH.
- Seat the seedling without crushing roots. Check contact again after the plug has absorbed solution.
- Place the vessel in its final light environment. Block direct light from the solution and shield excessive heat input.
- Record the level as roots extend. If the solution is being exhausted too early, revise the design or use a managed refill that preserves the established air zone; do not simply flood it back to the lid.
Reading: “Set It and Forget It” Hydroponic Lettuce (HS1488) ↗
03 / Concentration is still dynamic
No pump does not mean no chemistry. Water uptake and evaporation change concentration; plants remove different ions at different rates. Do not add a full batch of dry fertilizer every time a small amount of water is replaced.
For its lettuce example, UF/IFAS describes roughly 1.25 mS/cm EC and pH 5.5–6.0. Keep EC in its native unit: the publication’s approximate TDS value is not a universal meter conversion. Check your crop, source water and product instructions. Large fruiting plants require a much larger water budget and closer management than a small lettuce demonstration.
Reading: “Set It and Forget It” Hydroponic Lettuce (HS1488) ↗
04 / Inspect through harvest
Watch seedling moisture closely during establishment, then monitor level, temperature and crop development. A vessel outdoors can gain rainwater as well as lose water. If the level rises, check whether the developing air zone has been lost.
Harvest the crop while it remains healthy and before the root water supply is exhausted. Remove the plant, measure the remaining solution and record usable crop mass. Those two observations help improve the next vessel’s starting volume. Clean the tank and support between crops.
| Symptom | Inspect | Design lesson |
|---|---|---|
| Seedling dry on day one | Root-to-solution contact | Initial moisture cannot depend on future root growth. |
| Decline after topping up | Established air gap submerged | Preserve the upper root air zone. |
| Water exhausted before harvest | Starting volume and heat exposure | Increase crop water allowance or use a managed method. |
| Green water | Light entry through vessel or openings | Use opaque surfaces and fitted covers. |
Parts & buying criteria
Showing non-circulating 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 pump intake or lower roots; freeboard is deliberate.
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.
Supplier links can be added by the publisher. The criteria stand independently.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.
Supplier links can be added by the publisher. The criteria stand independently.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 Florida IFAS Extension“Set It and Forget It” Hydroponic Lettuce (HS1488) ↗
A small non-circulating lettuce example; seasonal and product assumptions apply.
The next useful connections.
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6 min + guided practice →