Arugula (Eruca sativa), also called salad rocket, is a fast-growing leafy crop that responds strongly to light.
But there is no scientifically established PAR, CO₂ and VPD recipe that applies to every greenhouse and every growth stage.
For arugula, published research gives us particularly useful evidence about:
- daily light integral (DLI)
- PPFD and photoperiod
- light spectrum
- CO₂ enrichment
- temperature
- nitrate accumulation
- fresh biomass
- polyphenols and other quality traits
The evidence for one precise arugula-specific VPD optimum is much weaker.
That means the better strategy is to measure the greenhouse environment and connect those measurements with crop growth and quality rather than following a rigid stage-by-stage target table.
Quick Reference
| Variable | What It Tells You | What Arugula Research Supports |
|---|---|---|
| PPFD / PAR | Photosynthetic light reaching the crop now | Arugula has been studied across a broad range of light intensities; intensity must be interpreted with photoperiod |
| DLI | Total photosynthetic light accumulated through the day | Direct greenhouse research found growth increased from very low DLI toward roughly 18 mol/m²/day, with slight fresh-weight decline above about 20 in one experiment |
| CO₂ | Carbon available for photosynthesis | Direct research comparing 400 and 800 ppm found higher photosynthetic assimilation and altered dry-matter and nutrient responses |
| VPD | Atmospheric evaporative demand | Useful for monitoring, but no validated stage-specific arugula optimum is established |
| Temperature | Influences growth, nitrate metabolism and water loss | Rocket generally performs as a cool-to-moderate-temperature leafy crop |
| Spectrum | Distribution of wavelengths | Can change biomass and polyphenol accumulation even when all treatments produce usable PAR |
These are research references, not universal crop specifications.
1. PAR and DLI Answer Different Questions
PPFD measures photosynthetic photon flux at one moment.
It is expressed in:
µmol/m²/s
It answers:
How much photosynthetically active light is reaching the arugula canopy right now?
DLI integrates PAR through the whole day.
It is expressed in:
mol/m²/day
It answers:
How much photosynthetic light did the crop receive today?
For constant artificial lighting:
DLI = PPFD × light-hours × 0.0036
For example:
150 µmol/m²/s × 16 h
≈ 8.6 mol/m²/day
200 µmol/m²/s × 16 h
≈ 11.5 mol/m²/day
250 µmol/m²/s × 16 h
≈ 14.4 mol/m²/day
300 µmol/m²/s × 16 h
≈ 17.3 mol/m²/day
In a greenhouse, sunlight changes continuously.
For that reason, logging PAR through the day is more useful than estimating daily light from one noon measurement.
2. Arugula Has Excellent Direct DLI Evidence
One controlled greenhouse experiment grew arugula across DLIs from approximately:
2 to 22 mol/m²/day
using:
- seasonal sunlight
- supplemental HPS lighting
- shade cloth
while maintaining a 16-hour day.
Arugula shoot fresh weight increased substantially as DLI increased from very low levels toward approximately:
18 mol/m²/day.
But the response did not continue indefinitely.
At DLIs above approximately:
20 mol/m²/day
shoot fresh weight began to decline slightly.
This is particularly useful because it directly challenges the idea that:
more daily light is always better.
3. Arugula Was Classified as a Medium-Light Leafy Green
Based on that greenhouse experiment, arugula was classified in approximately the:
10–20 mol/m²/day
DLI category.
This differs from crops such as kale and Swiss chard, which continued increasing in fresh weight across the full tested range.
For arugula:
fresh weight increased toward approximately 18 DLI
but began to diminish slightly above approximately 20 DLI.
This gives us a much stronger practical light reference than the old AquaHorti statement:
“Mature arugula needs 18–22 DLI.”
The research actually suggests that pushing beyond roughly 20 DLI may not continue improving fresh biomass.
4. Does That Mean 18 DLI Is the Universal Arugula Optimum?
No.
The greenhouse experiment provides a strong crop-specific reference.
But it still used one:
- production system
- cultivar environment
- photoperiod
- nutrient program
- harvest schedule
Other arugula systems operate successfully at different DLIs.
Therefore:
10–20 mol/m²/day is a useful research-based comparison region for actively growing arugula.
It should not be treated as a rigid pass/fail specification.
5. Another Greenhouse Arugula Study Averaged About 15.8 DLI
A separate hydroponic greenhouse experiment grew Eruca sativa for:
42 days
under an average DLI of approximately:
15.8 ± 6.9 mol/m²/day
and an average daily temperature of approximately:
25.6 ± 1.6°C.
The large DLI variation reflects an important greenhouse reality.
Natural sunlight does not deliver the same light every day.
That is exactly why DLI logging is valuable.
The crop experiences:
- bright days
- cloudy days
- seasonal change
rather than one fixed daily number.
6. Commercial Baby-Leaf Arugula Has Also Been Produced Around 17 DLI
Cornell and USDA research on:
Eruca sativa ‘Astro’
used greenhouse supplemental lighting and light-control algorithms to maintain approximately:
17 mol/m²/day.
Plants were grown hydroponically for approximately:
11–14 days
after germination.
This provides another successful production reference in the upper-mid teens.
Again:
17 DLI is a research environment, not a universal requirement.
7. A 2024 Study Compared 8.64 and 17.28 DLI
A controlled baby-green experiment compared arugula under:
8.64 mol/m²/day
and:
17.28 mol/m²/day.
Doubling DLI increased arugula shoot fresh mass by approximately:
38–73%
depending on the light-pattern treatment.
Shoot dry mass also increased.
This provides further evidence that moving from relatively low DLI toward the upper teens can strongly improve arugula growth.
8. But Photoperiod Pattern Did Not Affect Arugula as Strongly as Some Other Crops
The same study compared:
- conventional diurnal lighting
- alternating day/night light
- continuous light
while maintaining the same DLI.
Interestingly, arugula was less responsive to the temporal light pattern than lettuce or kale.
In other words:
DLI had a strong effect on arugula growth
while redistributing the same daily photons across the day and night had relatively limited effects on most arugula growth parameters in that experiment.
This is useful evidence that:
total daily light can sometimes matter more than the exact timing of those photons.
But this should not be generalized to every arugula production system.
9. Light Intensity and Photoperiod Still Matter
DLI is extremely useful.
But DLI does not describe everything.
Consider:
200 µmol/m²/s × 12 h
= 8.64 mol/m²/day
100 µmol/m²/s × 24 h
= 8.64 mol/m²/day
The total photon dose is the same.
The plant experiences a very different light pattern.
Research therefore still evaluates:
- PPFD
- photoperiod
- spectrum
- DLI
separately.
10. Direct Arugula Research Tested 100–350 PPFD
A hydroponic arugula experiment tested:
100 µmol/m²/s
200 µmol/m²/s
and:
350 µmol/m²/s
combined with photoperiods of:
3, 6, 12 and 24 hours.
This created DLIs ranging from only:
1.08
to more than:
30 mol/m²/day.
The experiment showed clearly that:
light intensity and duration are not simply “the higher, the better.”
11. 350 PPFD × 12 h Increased Fresh Weight
During the arugula harvest period, the treatment:
350 µmol/m²/s × 12 hours
produced average fresh weight around:
30.06 g
which was approximately:
38.5% higher
than the dark control used in that particular experiment.
But when the photoperiod was extended to:
24 hours
fresh weight declined.
This is another example of why arugula should not be managed by:
maximum PPFD + maximum photoperiod.
12. Nitrate Response Was Different From Fresh-Weight Response
Arugula is notable for its ability to accumulate nitrate.
Light strongly affects nitrate metabolism.
In the same experiment, stronger or properly timed lighting generally reduced nitrate accumulation compared with darkness.
For some parts of the experiment:
200 µmol/m²/s × 12 h
was particularly effective at limiting nitrate accumulation.
At other measurement points:
350 µmol/m²/s × 12 h
produced low nitrate levels.
This tells us something important:
The lighting treatment that produces the highest fresh weight is not necessarily the same treatment that optimizes nitrate concentration.
13. Therefore “Best Light” Depends on the Quality Goal
A grower may be optimizing for:
- maximum fresh biomass
- low nitrate
- tender texture
- high polyphenols
- short production time
- low electricity cost
Those are different objectives.
One light treatment may maximize fresh weight.
Another may produce a better nitrate profile.
Another may provide the best economic return.
That is why one universal PPFD recommendation is misleading.
14. A New 2026 Arugula Study Provides More Direct Lighting Evidence
A 2026 vertical NFT experiment tested arugula using:
- white LEDs
- red + blue LEDs
at two different distances from the canopy.
Actual PPFD ranged approximately:
193–258 µmol/m²/s
with DLIs around:
11.1–14.9 mol/m²/day
under a:
16-hour photoperiod.
These are particularly useful modern CEA reference conditions.
15. One White-Light Configuration Produced the Highest Fresh Biomass
In the 2026 experiment, the white-light treatment positioned:
20 cm from the canopy
produced the greatest fresh biomass.
Fresh mass reached approximately:
42.6 g/plant
in the first experiment
and:
70.9 g/plant
in the second experiment.
The same treatment also produced the highest measured total polyphenol concentration:
38.4 mg GAE/100 g fresh weight.
16. But the Study Does Not Prove “White Light Is Better”
The researchers specifically warned against making that conclusion.
The white and red-blue treatments differed not only in:
spectrum
but also in:
- lamp distance
- PPFD
- DLI
- overall radiation environment
Therefore, the result should be interpreted as:
one lighting configuration performed best
rather than:
white light is universally superior to red-blue light.
This is exactly the kind of methodological caution AquaHorti should preserve.
17. Nitrate Did Not Change Significantly in the 2026 Lighting Experiment
Interestingly, nitrate concentration in the 2026 NFT study did not differ significantly among the four lighting configurations.
Total polyphenols did.
This again demonstrates that crop-quality responses are trait-specific.
A lighting change can affect:
polyphenols
without producing a statistically significant change in:
nitrate.
18. Light Spectrum Matters — but the Response Is Context-Dependent
Previous arugula research has reported favorable responses to red-blue combinations.
The 2026 study did not reproduce a simple “red-blue is best” result.
Instead, the overall white-light configuration performed better for several measured traits.
The researchers concluded that arugula responses to lighting depend on the combined effects of:
- spectrum
- PPFD
- DLI
- lamp position
This is a much more defensible conclusion than recommending one universal spectrum.
19. CO₂ Has Direct Arugula-Specific Evidence
Arugula also has useful direct CO₂ research.
A controlled study grew two arugula varieties under:
400 ppm
and:
800 ppm CO₂.
Researchers simultaneously compared different nitrogen forms.
At 800 ppm, arugula showed a clear CO₂ fertilization response in physiological measurements.
Elevated CO₂ increased:
- internal leaf CO₂
- photosynthetic CO₂ assimilation
- water-use efficiency
and affected dry-matter accumulation.
20. But 800 ppm Did Not Simply Increase Every Yield Metric
This is where the study becomes particularly useful.
Higher CO₂ improved photosynthetic assimilation.
But fresh biomass, leaf area and other yield responses did not increase uniformly in the same way.
The crop accumulated additional assimilated carbon differently.
The researchers also observed changes in mineral concentration associated partly with increased dry matter.
This demonstrates:
Higher photosynthetic rate does not automatically translate proportionally into more fresh marketable biomass.
21. CO₂ Can Also Create Nutritional Tradeoffs
When plants accumulate more carbon and dry matter under elevated CO₂, concentrations of some mineral nutrients can decrease through a dilution effect.
This is important for leafy vegetables.
A greenhouse grower should not evaluate elevated CO₂ only by:
photosynthetic rate
or:
plant size.
Nutritional composition may also change.
22. Does Arugula Therefore Need 800 ppm CO₂?
No.
The experiment compared:
400 vs 800 ppm.
It demonstrated that elevated CO₂ changes arugula physiology.
It did not establish:
800 ppm as the universal commercial optimum.
Therefore, a defensible statement is:
800 ppm is a well-studied arugula CO₂ enrichment treatment that increased photosynthetic assimilation and water-use efficiency under controlled conditions.
It is not:
the required greenhouse CO₂ level.
23. CO₂ May Also Affect Disease Response
There is another reason not to treat elevated CO₂ as a purely positive variable.
Rocket plants exposed to:
800 ppm CO₂
have also been studied for disease response.
Under controlled conditions, elevated CO₂ increased the severity of some diseases such as:
Alternaria leaf spot
relative to standard CO₂ conditions.
Temperature interacted with this response.
This does not mean:
CO₂ enrichment causes disease.
It means greenhouse management must consider:
- crop growth
- plant physiology
- pathogens
- temperature
- humidity
together.
24. Temperature Is Particularly Important for Arugula
Arugula is generally considered a cool-to-moderate-temperature leafy vegetable.
Recent greenhouse literature synthesis indicates that approximately:
15–22°C
supports balanced rocket growth and nitrate metabolism in many systems.
When temperatures rise above approximately:
24–25°C
salad rocket can show:
- increased nitrate accumulation
- greater respiration
- increased water loss
- faster wilting
depending on cultivar and production conditions.
These values should be treated as literature references rather than rigid temperature specifications.
25. Temperature Changes How We Interpret PAR
Consider a bright arugula crop under:
18°C
and another under the same PPFD at:
29°C.
The PAR reading is identical.
But:
- respiration
- transpiration
- nitrate metabolism
- leaf temperature
- water demand
can be very different.
Therefore:
PAR should always be interpreted together with temperature.
26. What About VPD?
This is where the old AquaHorti article was far too precise.
It claimed stage-specific ranges such as:
0.8–1.3 kPa
1.0–1.8 kPa
and:
1.2–1.8 kPa
based on supposed repeated greenhouse measurements.
Current arugula-specific literature does not provide enough direct evidence to validate these as universal stage-specific optimum ranges.
Those numbers should therefore be removed.
27. VPD Is Still Useful
VPD describes atmospheric evaporative demand.
It is derived from:
- temperature
- relative humidity
When air becomes warmer or drier, VPD generally rises.
That can increase:
- transpiration
- water demand
- root-zone drying
- wilting risk
For a soft leafy crop such as arugula, this information is useful.
But VPD should be interpreted as:
an environmental diagnostic
rather than:
a universal crop setpoint.
28. What to Check When VPD Rises
If arugula VPD rises sharply, ask:
- Did temperature increase?
- Did humidity decrease?
- Did greenhouse vents open?
- Is root-zone water sufficient?
- Are leaves beginning to lose turgor?
- Is the condition temporary or sustained?
This is more useful than saying:
“1.8 kPa is good but 2.0 kPa is bad.”
Current arugula research does not justify that precision.
29. Very Low VPD Is Not Automatically Better
Low VPD usually means humid air.
That reduces atmospheric evaporative demand.
But persistently humid greenhouse conditions can also contribute to:
- condensation
- slow canopy drying
- disease-favorable conditions
The goal should not be:
minimum VPD.
The goal should be to understand and avoid persistent environmental extremes.
30. Seedling and Early Growth
Young arugula plants should not automatically receive the same environmental conditions as mature baby-leaf production.
During establishment, focus on:
- uniform emergence
- canopy light distribution
- temperature
- root-zone moisture
- compact early growth
Measure PPFD at the actual young canopy.
Avoid copying a mature-crop PPFD or DLI into the seedling stage without evidence.
31. Active Vegetative Growth
As arugula develops rapidly:
- leaf area increases
- carbon demand increases
- self-shading develops
- water demand rises
This is when DLI becomes especially valuable.
Direct greenhouse research shows that increasing daily light from very low levels toward the upper teens can substantially improve:
- fresh biomass
- dry biomass
- leaf development
But the response begins to flatten or decline when DLI becomes excessive for the system.
32. Pre-Harvest Quality
Near harvest, the production goal is no longer simply rapid growth.
Quality traits may include:
- fresh mass
- leaf tenderness
- nitrate concentration
- polyphenols
- color
- water content
- shelf life
Light treatments can affect these characteristics differently.
Therefore, do not assume:
the treatment producing the largest plant automatically produces the best marketable arugula.
33. Pre-Harvest and Post-Harvest Light Are Different Questions
A 2023 study examined light during the arugula harvesting/storage period.
It found that moderate red-blue LED treatments could help maintain:
- water content
- chlorophyll
- soluble sugars
- sensory quality
and reduce excessive nitrate accumulation compared with darkness.
For some sensory and storage objectives, approximately:
200 µmol/m²/s
with relatively short photoperiod treatments performed well.
These results apply to a specific harvesting/storage treatment.
They should not be turned into mature-production PPFD recommendations.
34. A Practical Greenhouse Monitoring Workflow
Step 1 — Measure PPFD at the Canopy
Measure where the leaves actually receive light.
Step 2 — Check Several Locations
Compare:
- greenhouse center
- edges
- structurally shaded areas
- dense canopy positions
Step 3 — Record DLI
Log PAR throughout the day.
Compare:
- sunny and cloudy days
- seasons
- greenhouse zones
- supplemental-light schedules
Step 4 — Track Temperature
Arugula quality and nitrate metabolism respond strongly to temperature.
Step 5 — Monitor CO₂
Compare crop-zone CO₂ with PAR during active photosynthesis.
Step 6 — Track Humidity and VPD
Use VPD to understand atmospheric water demand.
Step 7 — Check Root-Zone Water
High light and high atmospheric demand mean little without adequate water supply.
Step 8 — Record Crop Response
Track:
- fresh biomass
- leaf number
- leaf size
- crop uniformity
- harvest timing
If quality matters, also consider:
- nitrate
- polyphenols
- sensory quality
35. Practical Research-Based Reference Points
DLI
Arugula has unusually useful crop-specific evidence.
A greenhouse experiment covering approximately:
2–22 mol/m²/day
found fresh biomass increased toward approximately:
18 mol/m²/day
and began to decline slightly above:
20 mol/m²/day.
Therefore:
approximately 10–20 mol/m²/day
is a defensible research-based reference region for actively growing arugula.
It is not a universal optimum.
PPFD
Recent controlled arugula systems have successfully operated around:
190–260 µmol/m²/s
with a 16-hour photoperiod.
Other experiments have tested:
100–350 µmol/m²/s
with substantially different photoperiods.
Always interpret PPFD together with DLI.
CO₂
Direct research at:
400 vs 800 ppm CO₂
shows that elevated CO₂ can increase photosynthetic assimilation and water-use efficiency.
But growth and nutritional responses are more complicated than simply:
800 ppm = higher marketable yield.
Use 800 ppm as a research reference, not a universal setpoint.
VPD
There is currently insufficient arugula-specific evidence to publish one universal stage-specific VPD target.
Use VPD to understand atmospheric water demand and environmental changes.
Temperature
Approximately:
15–22°C
is a useful literature-based reference region for many salad-rocket production systems.
Higher temperatures can increase nitrate accumulation and water-loss risk.
Again, cultivar and system matter.
36. A Better Way to Think About Arugula Measurements
Instead of asking:
What PPFD does arugula require?
ask:
Is light limiting growth, and is that light evenly distributed?
Instead of:
What DLI is ideal?
ask:
How much light accumulated today, and are additional photons still increasing marketable biomass?
Instead of:
What CO₂ level should arugula have?
ask:
Does crop-zone CO₂ remain available while PAR is high, and does enrichment actually improve the production trait that matters?
Instead of:
What is the ideal VPD?
ask:
How strong is atmospheric water demand, and can the root zone support it?
Then ask:
Am I optimizing fresh biomass, nitrate, polyphenols, tenderness or production cost?
Those goals can lead to different environmental decisions.
Final Takeaway
Greenhouse arugula does not have one scientifically established PAR, CO₂ and VPD recipe for every growth stage.
But arugula has unusually strong crop-specific DLI evidence.
A direct greenhouse experiment spanning approximately:
2–22 mol/m²/day
found that shoot fresh weight increased as DLI rose toward approximately:
18 mol/m²/day
but began to decline slightly above:
20 mol/m²/day.
This supports approximately:
10–20 mol/m²/day
as a useful arugula light-reference region — not as a rigid requirement.
A separate 2024 controlled experiment found that increasing DLI from:
8.64 to 17.28 mol/m²/day
increased arugula fresh biomass by approximately:
38–73%.
Recent 2026 vertical NFT research also successfully produced arugula at approximately:
193–258 µmol/m²/s
and:
11.1–14.9 mol/m²/day.
One lighting configuration produced both the highest fresh biomass and highest polyphenol concentration, but the researchers correctly cautioned that spectrum, PPFD, DLI and lamp distance changed together.
CO₂ also matters.
Direct arugula research comparing:
400 and 800 ppm
found increased photosynthetic CO₂ assimilation and water-use efficiency under elevated CO₂, while fresh biomass and nutritional responses were more complex.
For VPD, current arugula-specific evidence does not justify the rigid stage-specific kPa ranges previously used in generic greenhouse guides.
The better strategy is therefore:
Measure PAR at the actual crop canopy.
Record DLI across the entire day.
Track temperature.
Monitor CO₂ during active photosynthesis.
Measure temperature, humidity and VPD together.
Then compare those measurements with the production trait that actually matters:
fresh biomass, nitrate level, polyphenols, tenderness or crop-cycle economics.
That provides a much stronger basis for greenhouse arugula production than unsupported stage-by-stage environmental targets.
References
Currey & Yost. Managing the Daily Light Integral for Leafy Greens. Greenhouse Product News, 2020.
Meng & Severin. Continuous Light Can Promote Growth of Baby Greens over Diurnal Light under a High Daily Light Integral. Environmental and Experimental Botany, 2024.
Mattson et al. Response of Hydroponic Baby Leaf Greens to LED and HPS Supplemental Lighting. Acta Horticulturae / USDA Agricultural Research Service, 2022.
Dickson et al. Evaluating Species-Specific Replenishment Solution Effects on Plant Growth and Root Zone Nutrients with Hydroponic Arugula and Basil. Horticulturae, 2023.
Schmidt & Zinkernagel. For a Better Understanding of the Effect of N Form on Growth and Chemical Composition of C3 Vascular Plants under Elevated CO₂—A Case Study with the Leafy Vegetable Eruca sativa. Horticulturae, 2021.
Li, Liu & Zhou. Effects of Light Intensity and Photoperiod on the Fresh Locking and Quality of Hydroponic Arugula in the Harvesting Period. Agronomy, 2023.
Rebolledo et al. Effects of LED Lighting Configurations on the Growth and Quality of Arugula (Eruca sativa Mill.) in a Vertical NFT System. Horticulturae, 2026.
Greenhouse Climate Shapes Nitrate Levels, Nutritional Quality, and Shelf Life in Leafy Vegetables: Species-Specific Responses. Frontiers in Plant Science, 2026.
Related AquaHorti Tools
For instantaneous PAR / PPFD measurements and checking greenhouse light distribution, see AquaHorti AH-Quantuv.
For recording changing greenhouse PAR throughout the day and measuring DLI, see AquaHorti AH-PARDLI.
For greenhouse monitoring where PAR, DLI, CO₂, temperature, humidity and VPD need to be reviewed together over time, see AquaHorti AH-200.