Tatsoi is a low-growing Asian leafy vegetable in the Brassica rapa group, recognizable by its dark green spoon-shaped leaves and compact rosette.
Its appearance can make it seem unusually tolerant. The plant stays close to the substrate, develops thick petioles and often continues looking healthy under cool conditions.
But visual appearance alone does not tell us whether the crop is receiving enough light or producing the desired nutritional quality.
Direct Tatsoi research shows that light intensity can strongly affect:
- biomass,
- nitrate and nitrite accumulation,
- photosynthetic efficiency,
- leaf area,
- protein,
- amino acids,
- and other quality characteristics.
What current research does not establish is one universal stage-by-stage formula such as:
seedling PAR = X
mature PAR = Y
CO₂ = exactly 900 ppm
VPD = exactly 0.9 kPa
for every Tatsoi crop.
A stronger greenhouse strategy is to use the measurements as connected indicators and keep experimental values tied to the conditions in which they were actually tested.
Tatsoi Has unusually Good Direct PPFD Research
One of the most useful Tatsoi studies compared plants at:
100 µmol/m²/s
200 µmol/m²/s
300 µmol/m²/s
400 µmol/m²/s
500 µmol/m²/s
PPFD.
Unlike generic leafy-green recommendations, these were treatments applied directly to Tatsoi.
The results showed that extremely low light created a clear quality problem.
At:
100 µmol/m²/s
the leaves contained approximately:
3.4 times more nitrate
and about:
34 times more nitrite
than plants grown at:
200 µmol/m²/s.
That is a very useful Tatsoi-specific result.
It demonstrates that light deficiency may affect the crop’s internal chemistry before the plant necessarily looks severely unhealthy.
Around 300 µmol/m²/s Performed Particularly Well in That Experiment
In the same controlled-environment study, approximately:
300 µmol/m²/s
produced a favorable combination of high biomass and low nitrate/nitrite content.
The authors identified roughly 300 µmol/m²/s as a useful level for balancing production and nutritional quality under their experimental conditions.
This is one of the rare cases where AquaHorti can give readers a fairly specific crop number based on direct evidence.
But we should still say:
300 µmol/m²/s was a strong experimental reference point, not a universal greenhouse optimum.
The study used controlled artificial lighting, defined spectra and a specific Tatsoi production system.
Natural-light greenhouses behave differently.
More Than 300 µmol/m²/s Did Not Keep Producing the Same Benefit
A useful finding from the same body of research is that Tatsoi biomass and leaf area increased strongly as PPFD increased from very low levels toward approximately 300 µmol/m²/s.
Above that level, further increases produced much smaller growth gains, while photosynthetic efficiency declined.
That means a grower should not interpret the experiment as:
500 µmol/m²/s is better than 300 because 500 is a larger number.
Instead, the evidence suggests diminishing returns.
This is exactly why PAR measurement should be used to identify whether light is limiting — not simply to maximize the meter reading.
PPFD and DLI Still Answer Different Questions
PPFD measures the instantaneous photosynthetic photon flux at the canopy.
DLI measures how many photons accumulate over the entire day.
For example, Tatsoi experiments have successfully used:
200 µmol/m²/s for a 16-hour photoperiod.
That equals approximately:
11.5 mol/m²/day DLI.
If PPFD is increased to:
300 µmol/m²/s for 16 hours
the corresponding DLI is approximately:
17.3 mol/m²/day.
These calculations are useful, but the two treatments are not automatically interchangeable with natural greenhouse light because sunlight continuously changes during the day.
A greenhouse can reach 500 µmol/m²/s briefly around noon and still deliver a relatively modest daily light total.
So for greenhouse Tatsoi:
PPFD tells you how bright it is now.
DLI tells you how much photosynthetic light the crop actually received that day.
200 µmol/m²/s Can Already Support Efficient Photosynthesis
A Tatsoi lighting experiment used:
200 µmol/m²/s PPFD
with:
16 hours of light per day.
Researchers then increased PPFD to:
300 µmol/m²/s
for three days before harvest.
The study found that 300 µmol/m²/s was not superior for all photosynthetic-performance measurements. The authors concluded that approximately 200 µmol/m²/s for 16 hours was already sufficient for efficient Tatsoi photosynthesis under the tested controlled conditions.
This is important because two different production questions are involved.
For photosynthetic efficiency:
200 µmol/m²/s may already be sufficient.
For nitrate reduction and some nutritional-quality objectives:
approximately 300 µmol/m²/s can provide additional benefits.
There is no contradiction.
The “best” light level depends on what you are trying to optimize.
Short-Term Pre-Harvest Lighting Can Reduce Nitrate
The same research tested a practical strategy that is especially relevant to controlled-environment growers.
Tatsoi was initially grown at:
200 µmol/m²/s
and then exposed to:
300 µmol/m²/s
during the final three days before harvest.
Increasing pre-harvest light reduced nitrate concentration.
This suggests an alternative to running the entire crop at very high light intensity.
Instead of using maximum lamp output throughout production, growers may be able to use targeted late-stage lighting to influence crop composition.
However, the response depended on the spectrum used.
Spectrum Matters — Not Just PAR
The 2019 Tatsoi study compared combinations of:
- 660 nm red,
- 640 nm red,
- 445 nm blue,
- and 731 nm far-red light.
Long-term red-only exposure was stressful for Tatsoi productivity.
Adding blue light to the red wavelengths improved several characteristics, including:
- biomass,
- leaf area,
- total protein,
- and essential amino-acid content.
The best-performing spectrum in that experiment combined approximately:
660 nm + 640 nm + 445 nm.
That means two grow lights producing the same PPFD do not necessarily produce identical Tatsoi crops.
Photon quantity and spectral composition both matter.
Far-Red Was Not Automatically Beneficial
Far-red photons are often discussed as a way to promote leaf expansion or modify plant architecture.
But Tatsoi-specific research gives an important warning.
Adding 731 nm far-red to the tested red-and-blue spectrum reduced growth and amino-acid content under the experimental conditions.
So it would be inappropriate to claim:
“Adding far-red improves Tatsoi rosette size.”
The actual response depends on dose, spectrum and crop objective.
For Tatsoi, direct evidence shows that more far-red is not automatically better.
Pre-Harvest Spectrum Can Alter Nitrate and Organic Acids
Another Tatsoi experiment started plants under:
200 µmol/m²/s
and raised total PPFD to:
300 µmol/m²/s
for three days before harvest using different spectral components.
Increasing blue light reduced nitrate and altered organic-acid composition.
Increasing red 640 nm produced a different response and substantially increased nitrite under that treatment.
This gives growers an important lesson:
Changing PPFD and changing spectrum at the same time can produce different biochemical responses.
So if leaf chemistry is the production target, PAR alone is not enough information.
Tatsoi Nutritional Quality Can Respond More Strongly to Light Intensity Than Spectrum
The direct Tatsoi research concluded that light intensity had a particularly strong influence on nitrate assimilation.
In other words, choosing an elaborate spectrum does not compensate for severe light deficiency.
This matters commercially.
A grower might invest substantial effort selecting a specific red/blue ratio while the crop is receiving only 100 µmol/m²/s.
For Tatsoi nitrate management, solving the basic photon shortage may be more important than fine-tuning the spectrum.
Tatsoi Can Be Grown Successfully in Greenhouse Hydroponics
University of Kentucky researchers tested Tatsoi in greenhouse hydroponic ponds under natural light.
Seeds were germinated around:
25°C,
and the production greenhouse used approximately:
16°C as the heating setpoint
and:
24°C as the ventilation setpoint.
The nutrient solution was maintained around:
EC 1.2 dS/m.
After approximately 30 days in the hydroponic production system, researchers reported high-quality Tatsoi plants.
These are useful documented production conditions.
But they should not become:
25°C germination + 16–24°C greenhouse + EC 1.2 = universal Tatsoi optimum.
The study was testing hydroponic production feasibility, not determining the optimum value of every environmental parameter.
Root-Zone Oxygen Also Matters
The Kentucky work compared aerated and non-aerated hydroponic ponds.
The project demonstrated that Tatsoi can be produced effectively in floating hydroponic systems and highlighted root-zone aeration as an important part of optimizing such production.
This is useful because many environmental articles focus only on:
PAR, CO₂ and VPD.
But a plant does not experience only its shoots.
Poor root-zone oxygen can limit crop performance even when canopy PAR and greenhouse climate appear normal.
For hydroponic Tatsoi, growers should therefore monitor:
- nutrient-solution EC,
- pH,
- temperature,
- dissolved oxygen or aeration,
- and root condition,
alongside canopy measurements.
Tatsoi Performs Well in Protected Greenhouse Culture
A Texas study compared numerous Asian leafy vegetables under greenhouse production.
In two greenhouse container trials, standard Tatsoi produced approximately:
148 g/plant
and:
139 g/plant
fresh shoot weight.
Tatsoi Savoy produced approximately:
159 g/plant
and:
112 g/plant.
Leaf Brix also varied between trials and cultivars, with Tatsoi Savoy reaching 5.52% in the second trial.
This is a useful reminder:
cultivar and growing environment can change both yield and composition.
So one environmental recipe should not be assumed to produce identical results in Tatsoi and Tatsoi Savoy.
Growing Season Changes Yield and Nutritional Composition
A two-year study in Poland compared Tatsoi and another Brassica rapa var. narinosa cultivar across different planting periods.
Changing the production period affected:
- total yield,
- marketable yield,
- rosette mass,
- dry matter,
- soluble sugars,
- carotenoids,
- vitamin C,
- and crude fibre.
The earlier production period produced greater total and marketable yield and higher vitamin C, while the later production period produced petioles with more dry matter and soluble sugars.
This is a particularly useful result for greenhouse growers.
Even if the crop variety and fertilizer remain the same, changing seasonal light and temperature can change both yield and quality.
This Is Why “Leaf Tenderness = VPD” Is Too Simple
The old Tatsoi article attributes rosette shape and leaf tenderness very directly to PAR, CO₂ and VPD.
Current direct evidence does not justify that level of certainty.
Tatsoi texture and leaf development can change with:
- cultivar,
- crop age,
- light intensity,
- spectrum,
- temperature,
- water availability,
- nutrient concentration,
- and seasonal conditions.
VPD may affect transpiration and tissue water status, but there is currently no strong Tatsoi experiment proving that:
0.7 kPa produces tender leaves
while:
1.2 kPa produces tough leaves.
Those statements should be removed.
There Is No Scientifically Established Tatsoi VPD Target
Direct Tatsoi controlled-environment studies have often been conducted around:
21°C day / 17°C night
and approximately:
55–65% relative humidity.
Those conditions demonstrate that Tatsoi can perform successfully in a moderate-humidity environment.
But the researchers were primarily testing lighting, not VPD.
Therefore those RH and temperature combinations should not be converted into a statement such as:
“The ideal Tatsoi VPD is X kPa.”
Current evidence is not strong enough for that conclusion.
What VPD Is Actually Useful For
VPD is still a useful greenhouse measurement because it describes atmospheric water demand.
When temperature rises or humidity falls, VPD generally rises.
That can increase potential leaf water loss.
But whether Tatsoi actually becomes stressed depends on:
- root-zone moisture,
- salinity,
- root oxygen,
- PPFD,
- airflow,
- temperature,
- and crop size.
So use VPD to answer:
“How strongly is the air demanding water from the plant?”
Then compare that with:
“Can the roots supply that water?”
That is much more defensible than treating VPD as a direct control for rosette shape.
Hot and Dry Conditions Are Not Ideal for Tatsoi
Commercial production guidance from SARE/Cornell describes Tatsoi as a crop that performs poorly under hot, dry conditions.
Their greenhouse transplant guidance uses approximately:
65–75°F / 18–24°C
for germination and growth.
Again, that is practical production guidance rather than an exact physiological optimum.
But it supports the broader conclusion that Tatsoi is better treated as a cool-to-moderate-temperature leafy crop rather than a heat-loving vegetable.
Temperature and Light Should Be Interpreted Together
A sunny greenhouse afternoon can increase both:
PPFD
and:
leaf temperature.
If the crop begins showing stress, the PAR reading alone cannot tell you whether the problem is:
- excessive photon load,
- elevated leaf temperature,
- insufficient water supply,
- or some combination.
Similarly, during winter the same greenhouse may have suitable air temperatures but very low DLI.
That is why recording PAR/DLI alongside temperature gives much more useful information than interpreting either value alone.
What About CO₂?
This is an area where the scientific evidence is much weaker than the old article suggests.
There is currently no strong body of Tatsoi-specific research showing that:
600 ppm is ideal for young plants
then:
800 ppm is ideal during rosette expansion
and:
1,000 ppm is ideal before harvest.
Those numbers create false precision.
Tatsoi is a C3 crop, so CO₂ availability can influence photosynthesis, but the magnitude of benefit depends on light, temperature, nutrition, canopy development and other factors.
Without Tatsoi-specific dose-response experiments, we should not present one exact enrichment range as established science.
The First CO₂ Question Should Be: Is There Actually a Deficit?
In a dense greenhouse crop, CO₂ may decrease during bright periods when ventilation is limited.
But that should be measured, not assumed.
A better workflow is:
- measure PPFD,
- measure canopy CO₂ during strong photosynthesis,
- determine whether CO₂ is falling below the surrounding outdoor or greenhouse baseline,
- then decide whether enrichment is likely to solve a real limitation.
If Tatsoi is receiving very little light, CO₂ enrichment may provide much less benefit because photon supply is already limiting photosynthesis.
CO₂ Cannot Correct Low DLI
Suppose winter Tatsoi receives very low daily light.
The crop may be photon-limited for much of the day.
Raising CO₂ substantially does not create photons.
This is why PAR/DLI measurements should normally be interpreted before assuming that CO₂ is the primary limiting variable.
For Tatsoi specifically, the strongest direct evidence currently relates to light quantity and quality, not to exact CO₂ enrichment targets.
Rosette Shape Is Not Controlled by One PAR Number
The characteristic flat Tatsoi rosette is strongly influenced by genetics.
Environmental conditions can modify leaf size, petiole elongation and overall architecture, but current evidence does not establish a simple relationship such as:
low PAR = open rosette
and:
high PAR = perfect compact rosette.
Light spectrum also modifies morphology, and long-term red-only or far-red-containing treatments can produce responses that are different from mixed red-and-blue light.
So rosette structure should be evaluated using:
- cultivar,
- spacing,
- PPFD,
- spectrum,
- temperature,
- and crop age,
rather than PAR alone.
More Compact Does Not Automatically Mean Better Quality
A crop can look compact because growth is well balanced.
But it can also remain small because light, root-zone conditions or nutrition are limiting.
Similarly, larger leaves can indicate productive growth or excessive stretching depending on context.
That is why Tatsoi quality should be evaluated with more than visual architecture.
Useful measurements include:
- fresh mass,
- dry matter,
- leaf area,
- nitrate level,
- Brix,
- color,
- marketability,
- and harvest consistency.
Nitrate Is One of Tatsoi’s Most Useful Quality Indicators
Tatsoi is particularly interesting for controlled-environment research because its nitrate content responds strongly to light intensity.
The direct comparison between 100 and 200 µmol/m²/s demonstrates how dramatic the difference can be under deficient light.
For commercial production, this means winter lighting decisions can affect more than harvest weight.
They may also influence leaf composition.
A grower measuring only plant size could miss this quality dimension.
Short-Term Lighting Before Harvest May Be More Efficient Than Running High Light All Cycle
The pre-harvest experiment provides a useful production concept.
Instead of maintaining:
300 µmol/m²/s
for the entire cycle, Tatsoi was grown at:
200 µmol/m²/s
and moved to stronger light near harvest.
The increased final-stage light reduced nitrate, although some photosynthetic indices suggested mild stress under the stronger treatment.
This suggests that lighting strategy can be dynamic.
The objective does not always need to be:
one fixed PPFD from transplant to harvest.
A Research-Based Tatsoi Reference Table
The following values come from actual Tatsoi experiments or greenhouse production studies.
They should remain tied to their original context.
| Research situation | Conditions | What it actually shows |
|---|---|---|
| PPFD experiment | 100–500 µmol/m²/s | Low light greatly increased nitrate/nitrite; ~300 performed well for biomass and nutritional quality |
| Photosynthesis experiment | 200 µmol/m²/s, 16 h | Efficient Tatsoi photosynthesis under controlled light |
| Pre-harvest lighting | 200 → 300 µmol/m²/s for final 3 days | Stronger pre-harvest light reduced nitrate |
| Spectrum study | 640/660 nm red + 445 nm blue | Mixed spectrum improved biomass, leaf area, protein and amino acids |
| Far-red treatment | +731 nm | Reduced growth and amino-acid content under the tested treatment |
| Greenhouse hydroponics | Heat ~16°C; vent ~24°C; EC ~1.2 dS/m | High-quality Tatsoi produced in about 30 days |
| Field seasonal comparison | Two summer–autumn production periods | Yield, vitamin C, sugars and dry matter changed with season |
| Texas greenhouse trials | Tatsoi and Tatsoi Savoy | Cultivar and production period changed fresh weight and Brix |
No study has demonstrated that these numbers can simply be combined into:
300 PPFD + 17 DLI + 900 ppm CO₂ + 0.9 kPa VPD = perfect Tatsoi.
That formula would be artificial.
A Better Greenhouse Tatsoi Monitoring Strategy
1. Measure PPFD at rosette height
Tatsoi grows very close to the substrate.
A PAR sensor positioned far above the plants may not represent the photon environment at leaf level.
Measure where the active leaves actually are.
2. Track DLI
A strong noon reading does not necessarily mean Tatsoi received enough daily light.
This is especially important during cloudy winter production.
3. Pay attention when PPFD stays below approximately 200 µmol/m²/s
Direct Tatsoi research shows that severe light deficiency can substantially increase nitrate and nitrite accumulation.
That does not mean every instant below 200 is harmful.
It means prolonged low-light production deserves attention.
4. Treat ~300 µmol/m²/s as a useful research reference, not a command
Under controlled conditions, approximately 300 µmol/m²/s provided a strong balance between biomass and nitrate quality.
Use it as a reference when evaluating your own system.
5. Record photoperiod
PPFD without photoperiod cannot tell you DLI.
A crop receiving 200 µmol/m²/s for 8 hours experiences a very different light environment from one receiving the same PPFD for 16 hours.
6. Monitor temperature and humidity together
Use VPD to understand atmospheric water demand.
Do not assume one VPD number controls Tatsoi tenderness or rosette shape.
7. Check CO₂ during bright periods
Determine whether depletion actually exists before deciding to enrich.
8. Monitor root-zone conditions
For hydroponics, measure:
- EC,
- pH,
- solution temperature,
- and root-zone oxygen/aeration.
Good canopy numbers cannot compensate for poor root-zone function.
9. Consider pre-harvest lighting separately
If nitrate quality is an important objective, a short increase in PPFD before harvest may deserve testing rather than increasing light throughout the whole crop cycle.
10. Record cultivar
Standard Tatsoi and Tatsoi Savoy can differ in fresh weight, Brix and appearance.
Environmental records are much more useful when cultivar identity is preserved.
What Should Growers Actually Optimize?
Current Tatsoi research supports several clear priorities.
Avoid prolonged severe light deficiency.
At 100 µmol/m²/s, nitrate and nitrite accumulation increased dramatically compared with 200 µmol/m²/s.
Do not assume PPFD above 300 µmol/m²/s keeps producing proportional benefits.
Growth responses showed diminishing returns beyond this region under controlled conditions.
Consider DLI as well as instantaneous PPFD.
200 µmol/m²/s for 16 hours provides approximately 11.5 mol/m²/day, while 300 µmol/m²/s over the same period provides about 17.3 mol/m²/day.
Use spectrum as a quality variable.
Mixed red and blue light performed better than long-term red-only light in direct Tatsoi research.
Do not make unsupported CO₂ claims.
There is not enough Tatsoi-specific research to establish a universal 800-, 900- or 1,000-ppm optimum.
Do not turn VPD into a leaf-tenderness control knob.
VPD describes atmospheric water demand; texture and architecture depend on many additional factors.
And:
remember that the crop has roots.
Hydroponic nutrient concentration, oxygenation and water availability remain part of the same production system.
Key Takeaway
Tatsoi is actually one of the better-researched Asian leafy greens for controlled-environment lighting.
Direct experiments have compared 100, 200, 300, 400 and 500 µmol/m²/s PPFD.
At 100 µmol/m²/s, Tatsoi accumulated approximately 3.4 times more nitrate and 34 times more nitrite than at 200 µmol/m²/s.
Around 300 µmol/m²/s produced a strong combination of biomass and nutritional quality under the controlled conditions tested, while further increases showed diminishing benefits.
Separate research found that 200 µmol/m²/s for a 16-hour photoperiod was already sufficient for efficient photosynthesis, while increasing PPFD to 300 µmol/m²/s for the final three days could reduce nitrate content.
Light spectrum also matters: mixed red and blue performed better than long-term red-only light, while the tested far-red supplementation reduced growth and amino-acid content.
For greenhouse growers, the stronger strategy is therefore to:
measure PPFD at rosette height, track DLI, monitor temperature and humidity, measure CO₂ before assuming enrichment is necessary, maintain a healthy root zone, and evaluate nutritional quality as well as biomass.
That provides a far more defensible picture of Tatsoi production than a fixed stage-by-stage PAR / CO₂ / VPD recipe.
References
Viršilė, A., Brazaitytė, A., Vaštakaitė-Kairienė, V., Jankauskienė, J., Miliauskienė, J., Samuolienė, G., Novičkovas, A., & Duchovskis, P. (2019). Nitrate, nitrite, protein, amino acid contents, and photosynthetic and growth characteristics of tatsoi cultivated under various photon flux densities and spectral light compositions. Scientia Horticulturae, 258, 108781. DOI: 10.1016/j.scienta.2019.108781.
Simanavičius, L., & Viršilė, A. (2018). The effects of LED lighting on nitrates, nitrites and organic acids in tatsoi. Research for Rural Development, 24. DOI: 10.22616/rrd.24.2018.057.
Viršilė, A. et al. (2018). LED lighting for reduced nitrate contents in green vegetables. Acta Horticulturae, 1227. DOI: 10.17660/ActaHortic.2018.1227.85.
Kalisz, A., Sękara, A., Gil, J., Grabowska, A., & Cebula, S. (2013). Effect of Growing Period and Cultivar on the Yield and Biological Value of Brassica rapa var. narinosa. Notulae Botanicae Horti Agrobotanici Cluj-Napoca, 41(2), 546–552.
Anderson, R. G. Yield of Brassica ‘Mei Qing Choi’ and ‘Tatsoi’ in Hydroponic Greenhouse Production. University of Kentucky Agricultural Experiment Station.
Niu, G. et al. (2021). The Performance of Representative Asian Vegetables in Different Production Systems in Texas. Agronomy, 11, 1874.