Endive (Cichorium endivia) is a cool-season leafy vegetable that includes two closely related forms: curly endive (C. endivia var. crispum) and broad-leaved escarole (C. endivia var. latifolium).
Like lettuce, endive responds strongly to light, temperature and water availability. But treating it as simply “another lettuce” can be misleading.
Research shows that endive growth, leaf morphology and quality respond differently to light intensity, light spectrum, daily light exposure and water status.
There is also an important limitation:
There is no scientifically validated table assigning one exact PAR, CO₂ and VPD value to every stage of greenhouse endive growth.
Published studies use different cultivars, lighting systems, seasons and production methods. Their environmental values are therefore best used as reference conditions, not universal targets.
What Climate Does Greenhouse Endive Prefer?
FAO greenhouse-production guidance describes both endive and escarole as cool-season crops and gives an optimum growth temperature of approximately:
15–18°C
with relative humidity around:
70%
The same guidance notes that temperatures around 20–25°C combined with long days can encourage flowering.
That temperature range is a much stronger scientific starting point than assigning arbitrary VPD numbers to five different crop stages.
At 15–18°C and approximately 70% RH, air VPD is roughly 0.5–0.6 kPa, assuming leaf temperature is close to air temperature.
That does not mean 0.5–0.6 kPa is a universal endive VPD optimum. Leaf temperature, airflow, irrigation and radiation all influence the actual plant response.
PAR: How Much Light Has Been Used in Endive Research?
Several experiments give us useful reference points.
One controlled-light study compared endive grown under approximately:
62–78 µmol/m²/s
with plants receiving approximately:
100–102 µmol/m²/s.
The higher-light treatments increased fresh weight, dry weight and leaf area. A red-enriched spectrum also increased growth compared with the other spectrum tested.
This tells us that endive can respond positively to increased PPFD under low-light indoor conditions.
It does not establish 100 µmol/m²/s as the optimum PPFD for commercial greenhouse endive.
The important distinction is between:
an experimental treatment that produced a response
and
a universal crop recommendation.
Those are not the same thing.
Seedling Light: A Useful Research Reference
A greenhouse study involving baby-leaf endive initially raised plants under controlled conditions of approximately:
- 190 ± 10 µmol/m²/s PPFD
- 12-hour photoperiod
- 20°C
- 70–80% relative humidity
before greenhouse production.
At 190 µmol/m²/s for 12 hours, the corresponding DLI is approximately:
8.2 mol/m²/day
Again, this is a documented research condition, not proof that every endive seedling requires exactly 190 µmol/m²/s.
But it provides a much more defensible reference than unsupported claims such as “80–140 µmol/m²/s is the ideal germination range.”
Why DLI Matters More Than a Single PAR Reading
PPFD tells you how much photosynthetically active light reaches the canopy at one moment.
DLI tells you how much photosynthetically active light accumulates across the day.
That distinction becomes especially important in a greenhouse.
A crop may measure:
250 µmol/m²/s at noon
on both Monday and Tuesday.
But Monday may be sunny for eight hours while Tuesday is heavily overcast for most of the day.
The midday PAR measurement is similar.
The total light received by the crop is not.
For greenhouse endive, tracking DLI therefore gives more useful context than relying only on one midday PAR measurement.
What Supplemental-Lighting Research Shows
A study involving lettuce, escarole and curly endive in an aquaponic system compared natural light with natural light plus supplemental white LEDs.
The supplemental lighting provided:
173 µmol/m²/s for 16 hours
equivalent to approximately:
10 mol/m²/day of supplemental DLI.
The supplemental treatment increased endive growth and photosynthetic activity during winter production.
There is an important detail here:
The 10 mol/m²/day came from the supplemental lighting component. The plants were also receiving natural light.
So this study should not be interpreted as proving that “10 mol/m²/day is the optimum total DLI for endive.”
Instead, it demonstrates that additional daily light can improve endive production when natural winter light is limiting.
More Light Is Not Always Better Quality
Another greenhouse experiment with escarole compared plants receiving 100%, 70% and 50% of incident PPFD.
Full light produced greater dry-matter accumulation later in the crop cycle.
However, plants under 50% incident PPFD showed several quality differences, including:
- thinner leaves,
- lower cellulose,
- lower lignin,
- and better visual characteristics.
The authors concluded that reducing PPFD under naturally high-light conditions can improve several morphological and quality characteristics of escarole.
This is particularly important for growers.
Maximum biomass and maximum market quality are not necessarily the same target.
It also shows why a statement such as “endive always needs more PAR as it matures” would be too simplistic.
A Better Way to Interpret Endive Light
Instead of following rigid stage-by-stage PPFD numbers, consider the actual production environment.
During low-light periods
Supplemental lighting can raise DLI and improve growth.
Measure PPFD at canopy height and calculate or log the accumulated DLI.
During high-light periods
More PPFD may increase biomass, but excessive radiation and heat can reduce desirable leaf characteristics.
Shading may therefore be useful when radiation and greenhouse temperature become excessive.
As the canopy grows
Move the PAR sensor so that it continues measuring at approximately crop-canopy level.
The reading above a young plant and the reading inside a mature canopy can be very different.
What About CO₂?
This is one of the biggest problems in the original article.
There is currently not enough endive-specific evidence to justify recommendations such as:
400–600 ppm during germination
then
700–1000 ppm during vegetative growth
then
600–800 ppm before harvest.
Those numbers look precise, but precision does not make them scientifically established.
A better principle is to monitor whether CO₂ becomes depleted when a greenhouse is closed and photosynthesis is active.
Michigan State University notes that densely cropped closed greenhouses can sometimes fall to approximately 200 ppm CO₂ because plants are consuming carbon faster than fresh air is entering.
For greenhouse crops in general, increasing CO₂ increases photosynthesis until diminishing returns become substantial, commonly around approximately 1,000 ppm, although the response is species-, light- and temperature-dependent.
That is general greenhouse physiology — not an endive-specific enrichment prescription.
For endive growers, the practical first question should therefore be:
Is canopy CO₂ being depleted during the bright part of the day?
before asking:
What enrichment concentration should I use?
CO₂ and Light Must Be Considered Together
Plants require light energy to use CO₂ efficiently.
This means high CO₂ does not automatically compensate for insufficient light.
Conversely, adding supplemental lighting while CO₂ becomes strongly depleted can limit the value of that extra light.
Michigan State University describes this interaction clearly: low CO₂ reduces photosynthesis and lowers the light level at which photosynthesis begins to saturate.
So PAR, DLI and CO₂ should not be managed as independent numbers.
They interact.
What Does VPD Tell Us?
VPD describes the difference between the amount of water vapor the air could hold and the amount it currently contains.
As VPD rises, the atmosphere has greater drying power.
That influences:
- transpiration,
- stomatal behavior,
- plant water demand,
- nutrient transport,
- and potentially leaf quality.
But current research does not provide evidence for a precise five-stage VPD schedule for endive.
That is why the original ranges such as:
0.4–0.7 → 0.6–1.0 → 0.8–1.2 kPa
should not be presented as established endive requirements.
Water Status Matters
Research on escarole confirms that water stress affects gas exchange.
Under drought conditions, reductions in stomatal conductance can reduce CO₂ assimilation and photosynthesis. Researchers studying escarole measured photosynthesis, transpiration and stomatal conductance specifically to evaluate this response.
This provides a more scientifically defensible interpretation of VPD:
The goal is not to hit one magic VPD number. The goal is to prevent atmospheric water demand from exceeding the root system’s ability to supply water.
A high VPD may be manageable when irrigation, root health and temperature are well controlled.
The same VPD may create stress when root-zone water availability is limited.
Research-Based Reference Conditions
The published literature provides several useful reference environments:
| Research situation | PPFD / DLI | Temperature / RH | What it tells us |
|---|---|---|---|
| Seedling/growth-chamber study | ~190 µmol/m²/s, 12 h; ~8.2 mol/m²/day | 20°C, 70–80% RH | A documented establishment condition |
| Controlled LED study | ~62–102 µmol/m²/s | Controlled environment | Higher tested PPFD increased growth |
| Winter aquaponic supplementation | 173 µmol/m²/s × 16 h; 10 mol/m²/day supplemental DLI | Greenhouse | Supplemental light improved endive growth |
| FAO greenhouse guidance | Natural greenhouse light | 15–18°C; ~70% RH | Practical cool-season climate reference |
| High-radiation greenhouse study | 100%, 70%, 50% incident PPFD | Greenhouse | Less light improved some quality traits |
The most important point is that these numbers come from different experiments.
They should not be combined into one supposedly exact “endive recipe.”
Practical Greenhouse Measurement Workflow
A more reliable endive-management strategy is straightforward.
Measure PPFD at canopy level
Take measurements where the leaves actually intercept the light.
Do not rely solely on fixture output specifications or a sensor mounted far above the crop.
Track DLI
For variable sunlight, monitor light across the full day rather than judging the crop from one noon reading.
Monitor temperature and humidity together
Endive is fundamentally a cool-season crop.
A humidity reading without temperature does not describe atmospheric drying demand adequately.
Watch CO₂ during bright periods
If the greenhouse is closed, check whether CO₂ falls significantly as crop photosynthesis increases.
Keep sensor positions representative
As the crop becomes larger, reposition sensors so the measurements continue to represent the active canopy.
Endive vs. Escarole
Curly endive and escarole belong to the same species, Cichorium endivia, but their leaf architecture differs substantially.
Research has documented considerable variation in leaf morphology and photosynthetic characteristics between commercial endive and escarole cultivars.
That is another reason not to assume that one exact light or VPD value applies to every C. endivia cultivar.
Cultivar matters.
Key Takeaway
Scientific research does not support a universal schedule that assigns exact PAR, CO₂ and VPD values to every stage of greenhouse endive production.
What the evidence does support is more useful:
Endive prefers relatively cool growing conditions.
Its growth responds to both PPFD and total daily light.
Supplemental DLI can improve winter production when natural light is limiting.
Under high natural radiation, reducing light can improve some leaf-quality characteristics even when full light produces more dry matter.
Water status, humidity and atmospheric demand influence stomatal behavior and photosynthesis.
And CO₂ should be evaluated together with light rather than treated as an independent number.
For growers, the best strategy is therefore not to chase a rigid environmental recipe.
It is to measure PAR at canopy level, track DLI, monitor temperature, humidity and CO₂, and adjust the greenhouse according to the crop’s actual environment.
References
FAO. Good Agricultural Practices for Greenhouse Vegetable Production in the South East European Countries — Escarole and Endive (Cichorium endivia).
Flores, M., Urrestarazu, M., Amorós, A., & Escalona, V. H. High intensity and red enriched LED lights increased the growth of lettuce and endive. Italian Journal of Agronomy.
Supplemental Daily Light Integral by LED Light to Improve the Growth of Leafy Vegetables in Aquaponics System. Acta Horticulturae.
Photosynthetic Photon Flux Density Levels Affect Morphology and Bromatology in Cichorium endivia var. latifolia Grown in a Hydroponic System.
Reduction of Nitrate Content in Baby-Leaf Lettuce and Cichorium endivia Through the Soilless Cultivation System, Electrical Conductivity and Management of Nutrient Solution.
Romero-Muñoz, M. et al. The Use of Ecological Hydromulching Improves Growth in Escarole (Cichorium endivia L.) Plants Subjected to Drought Stress. Agronomy.