- Distinguish tipburn observations from bolting.
- Investigate calcium delivery, roots and canopy conditions together.
- Measure correction results using comparable crop cohorts.
01 / Two different problems can share one crop
Tipburn describes damage at leaf margins, often on young inner leaves of a developing head. Bolting is the transition toward a flower stalk. Neither term should be assigned to every brown or stretched lettuce plant: pests, root disease and chemical injury can produce overlapping symptoms.
Photograph the youngest and oldest leaves, inspect undersides for insects, and check the center for stem elongation. Record cultivar, sowing and transplant dates, first symptom date and the fraction of plants affected. Illinois Extension links seedstalk development with temperature, daylength and plant age; these are different clues from a damaged leaf margin.
Reading: Lettuce: Home Vegetable Gardening ↗
02 / Tipburn is a delivery question, not an automatic supplement order
Calcium supply to rapidly growing tissue can be inadequate even when a solution contains calcium. The Cornell lettuce handbook connects tipburn management with air movement and growth conditions. That does not establish that all cases have adequate nutrition: check the actual fertilizer recipe, source water and roots as well.
An EC reading cannot isolate calcium. Additional calcium changes the formulation and may add other ions, depending on the product. Diagnose a real shortage before supplementing. Brown tissue will not become healthy again, so judge a correction from subsequent growth or a comparable new crop rather than expecting old margins to recover.
Reading: Cornell Controlled Environment Agriculture Hydroponic Lettuce Handbook (2013) ↗ · Hydroponic Nutrient Solutions (G6984) ↗
03 / Measure where the leaves grow
Place temperature and humidity sensors near the canopy without letting a lamp or splash dominate the reading. Compare crowded centers with open edges. Confirm that circulation reaches the crop without creating excessive drying, and distinguish air recirculation from replacing warm, moist room air.
Record daily light integral as well as timer hours. For constant light, DLI equals PPFD × hours × 0.0036. For example, 250 micromoles per square meter per second for 16 hours supplies 14.4 moles per square meter per day. This arithmetic describes light received; it is not a universal lettuce prescription. Sunlight and changing dimmer output require integration over time.
Cornell’s lighting and airflow results apply to its tested cultivars and production setup. Do not scale a commercial airflow figure directly into a small enclosure or infer canopy conditions from a fan’s maximum box rating. Use the light chapter to compare a measured grid and crop-specific targets.
Reading: Measuring Daily Light Integral in a Greenhouse (HO-238-W) ↗ · Cornell Controlled Environment Agriculture Hydroponic Lettuce Handbook (2013) ↗
04 / Manage bolting through timing and cultivar choice
Virginia Cooperative Extension recommends slow-bolting or heat-resistant cultivars to extend the lettuce season. This is relative tolerance, not immunity. Choose seed for the intended season and production system, then compare actual harvest timing and quality in your space.
Air and solution temperatures are separate measurements. Cooling the reservoir alone does not demonstrate that the shoot is in a suitable climate. Record warm periods at the canopy, seasonal daylength or lighting schedule, and whether harvest was delayed beyond the desired stage. A flowering plant will not reliably return to its original marketable head because nutrients changed.
| Observation | Investigate | Avoid assuming |
|---|---|---|
| Inner margins brown; crowded heads | Calcium delivery, roots, recipe and canopy airflow | That more calcium is always the remedy |
| Center extends into a seedstalk | Cultivar, age, canopy heat and daylength | That low EC caused the stalk |
| Margins damaged across exposed leaves | Salt injury, root condition and localized drying | That all edge damage is tipburn |
| Distorted leaves with insects underneath | Pest identification and crop-appropriate management | That fertilizer will remove the cause |
Reading: Leafy Green Vegetables (426-408 / SPES-785P) ↗ · Lettuce: Home Vegetable Gardening ↗
05 / Run a small, interpretable correction trial
Start by repairing any clear delivery or measurement fault. Then change one practical variable at a time where crop welfare permits, documenting the new setting and date. Keep a comparison cohort only if doing so does not knowingly prolong a damaging condition. Avoid judging airflow, lighting, cultivar and nutrition after changing all four together.
Record the number of affected plants over the total inspected, the location of damage and the harvest stage. Twelve affected heads out of forty is 30%; three out of ten is also 30%, but a much smaller observation. Compare like ages and cultivars rather than presenting one favorable tray as proof.
- Verify pH, EC, recipe, roots and actual water delivery.
- Log canopy temperature, humidity, lighting and observed air movement.
- Choose the first correction from a documented fault or crop-specific guidance.
- Mark plants or cohorts and use the same inspection method each time.
- Track new damage and harvest quality; seek extension diagnosis when the pattern is unclear.
Reading: Cornell Controlled Environment Agriculture Hydroponic Lettuce Handbook (2013) ↗
06 / Worked case: acceptable meters, damaged hearts
Suppose the recorded pH and EC match a lettuce program, but inner margins brown as the canopy closes. This supports investigating the canopy and calcium delivery; it does not rule out a mixing error, root problem or individual nutrient shortage. Inspect those causes before modifying the formula.
FIELD QUESTIONWill adding calcium or lowering light immediately identify the cause?
No. Each changes a different part of the system, and old damage persists. Verify nutrition and roots, measure the canopy, document a justified correction and assess new growth. Obtain diagnostic help for unexplained or spreading injury.
Reading: Hydroponic Nutrient Solutions (G6984) ↗ · Cornell Controlled Environment Agriculture Hydroponic Lettuce Handbook (2013) ↗
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 Illinois ExtensionLettuce: Home Vegetable Gardening ↗
Tipburn symptoms, pests, heat, daylength and seedstalk development.
- Cornell University CEA Program (M. Brechner and A. J. Both)Cornell Controlled Environment Agriculture Hydroponic Lettuce Handbook (2013) ↗
Pond-stage lighting: supplemental 100–200 µmol/m²/s at plant level for a total of 17 mol/m²/d of natural plus supplemental light; the 17 mol/m²/d target having to be matched with downward airflow to prevent tip burn, and the statement that without that airflow the authors were not able to go over 12 mol/m²/d, with the caveat that the data are for cultivar Ostinata only.
- University of Missouri ExtensionHydroponic Nutrient Solutions (G6984) ↗
Solution preparation, elemental nutrition and measurement.
- Purdue University ExtensionMeasuring Daily Light Integral in a Greenhouse (HO-238-W) ↗
DLI, PPFD and light measurement.
- Virginia Cooperative ExtensionLeafy Green Vegetables (426-408 / SPES-785P) ↗
Lettuce climate, bolting, cultivar selection and cultural problems. Soil fertilizer rates are not applied to hydroponics.
The next useful connections.
Light, temperature and humidity
Measure the growing environment at the canopy and root zone, then adjust one limiting condition at a time.
Interactive tool · 6 min + guided practice →Nutrients & mixingNutrient deficiency symptoms in hydroponics: narrow the possibilities, then test
Leaf position and symptom patterns guide an investigation. Meter readings, the mixing record and laboratory results determine the correction.
6 min + guided practice →Buying guidesChoosing grow lights for leafy greens: buy the DLI, not the watts
A grow light is bought against the daily light integral your greens need at canopy height; photon flux and efficacy get you there, watts do not.
Interactive tool · 8 min + guided practice →Crops & environmentHydroponic lettuce from seed to harvest: EC, pH, timing and spacing
A lettuce-only crop plan: published germination, transplant, solution, temperature, light and harvest figures, and the calendar that ties them together.
7 min + guided practice →