Greenhouse strawberries are often managed using a list of environmental targets: a certain light level, a CO₂ concentration, a temperature range and a VPD setpoint.
The problem is that strawberries do not respond to these variables independently.
CO₂ enrichment can increase photosynthesis and yield, but its benefit depends on temperature and available light. Temperature influences flower induction, flowering speed, berry size and fruit quality. VPD affects plant water demand and can also change the timing of pollen release. Root-zone moisture determines whether the plant can meet atmospheric water demand.
There is therefore no scientifically validated stage-by-stage recipe assigning one exact CO₂ concentration and VPD value to every greenhouse strawberry crop.
Cultivar type matters as well. Short-day, June-bearing and everbearing/day-neutral strawberries do not necessarily respond to temperature and photoperiod in the same way.
For growers, the stronger approach is to understand what research actually shows and then measure the environment the crop is experiencing.
Light Is Important — But This Article Focuses on Climate
Strawberries obviously require adequate photosynthetic light.
However, AquaHorti already has a dedicated guide covering strawberry PPFD and DLI from establishment through fruiting.
For greenhouse climate management, the more useful question is:
Once adequate light is available, are temperature, CO₂, VPD and root-zone conditions allowing the plant to use that light effectively?
That is the focus here.
A single bright afternoon cannot compensate for an unsuitable flowering temperature, severe water stress or poorly managed CO₂.
Likewise, elevated CO₂ cannot compensate indefinitely for insufficient daily light.
CO₂ Enrichment Can Increase Strawberry Yield
Strawberry has direct greenhouse CO₂-enrichment research.
A study using the cultivar ‘Sagahonoka’ compared approximately:
400 µmol/mol CO₂
with:
800 µmol/mol CO₂.
Across two production years, marketable yield under 800 µmol/mol was approximately:
20–31% higher
than under the 400 µmol/mol treatment.
The higher-CO₂ plants also produced more marketable fruits and greater average fruit weight, and fruit Brix was higher during part of the production season.
That provides strong evidence that greenhouse strawberries can respond positively to CO₂ enrichment.
But it does not prove that:
800 ppm is the universal optimum strawberry CO₂ concentration.
The experiment compared defined treatments under a particular cultivar and production system.
Local CO₂ Enrichment Can Be More Efficient Than Raising the Whole Greenhouse
Another protected-cultivation study tested a crop-local CO₂ system that delivered CO₂ through tubes positioned close to the strawberry canopy.
Compared with conventional enrichment, the local system increased canopy CO₂ concentration by approximately:
100–200 µmol/mol
even while roof ventilation was operating.
The crop-local treatment increased:
- average fruit weight by roughly 10–26%,
- cumulative fruit number by about 13%,
- cumulative marketable yield by about 22%,
while reducing cumulative fuel use by approximately 27%.
This is an important greenhouse lesson:
CO₂ concentration at the crop canopy can matter more than simply achieving a high reading somewhere else in the greenhouse.
It also shows why sensor position matters.
CO₂ Should Be Measured Near the Active Canopy
A CO₂ controller mounted far from the crop may not represent what strawberry leaves experience.
During strong photosynthesis, local CO₂ can be depleted around dense foliage.
At the same time, ventilation can bring outside air into some parts of the greenhouse faster than others.
So the most useful question is not:
“What is the greenhouse CO₂ setting?”
It is:
“What CO₂ concentration is the active strawberry canopy actually experiencing during photosynthesis?”
This is particularly important during bright periods when CO₂ demand is highest.
More CO₂ Is Not Always Better
Older strawberry research compared approximately ambient CO₂ with much higher concentrations and found increased growth and fruit production under suitable environmental conditions.
But experiments combining CO₂ and temperature show an important limitation:
the CO₂ response changes with temperature.
One controlled study found that elevated CO₂ improved strawberry production under lower-temperature conditions but could reduce yield when combined with high temperature.
The negative response was associated with fewer inflorescences and smaller flower clusters during flower induction.
This means:
high CO₂ does not cancel out poor temperature management.
Temperature Can Be More Important Than CO₂ During Flowering
Strawberry reproductive development is highly temperature sensitive.
A classic controlled study using the cultivars ‘Korona’ and ‘Elsanta’ tested:
- day temperatures from 12 to 27°C,
- night temperatures from 6 to 12°C,
- and photoperiods from 12 to 16 hours.
Under those particular short-day cultivars and experimental conditions, flower emergence was strongest around:
18°C day temperature
and:
12°C night temperature.
Photoperiods of approximately 12–13 hours also promoted flower emergence more effectively than longer photoperiods.
But this result should not be turned into:
Every greenhouse strawberry must be grown at 18/12°C.
The experiment involved specific cultivars with particular photoperiod responses.
Day-neutral and everbearing cultivars can behave differently.
Cultivar Changes the Optimum Temperature
This becomes especially clear in newer research.
A 2026 controlled-environment study compared six everbearing strawberry cultivars under five day/night temperature programs:
15/7°C
18/10°C
21/13°C
24/16°C
27/19°C
with a 16-hour photoperiod and DLI of 15 mol/m²/day.
The optimum temperature for yield efficiency differed substantially among cultivars.
Estimated optimum temperatures ranged from approximately:
17.9 to 22.7°C
depending on cultivar.
Above the cultivar-specific optimum, yield losses were associated mainly with reduced berry size; below it, yield was more limited by fruit number.
This is a very important result for greenhouse growers:
there is no single ideal strawberry temperature independent of cultivar.
Temperature Also Changes Berry Quality
Temperature after flowering affects more than final yield.
Research comparing:
18/12°C
25/12°C
25/22°C
30/22°C
day/night temperatures found that cooler conditions generally favored several strawberry fruit-quality characteristics.
As temperatures increased, researchers observed reductions in:
- soluble solids,
- titratable acidity,
- soluble-solids-to-acid ratio,
- ascorbic acid,
- and several sugars.
The 30/22°C treatment also inhibited plant and fruit growth under the conditions tested.
So warmer temperatures may accelerate some developmental processes while simultaneously reducing berry size or quality.
That is why “faster growth” should not automatically be interpreted as “better production.”
Flower Induction and Fruit Production Are Different Problems
A useful way to think about strawberry climate is to separate:
flower induction
from:
fruit development.
Environmental conditions that promote flower initiation are not necessarily identical to the conditions that maximize fruit expansion and ripening.
In short-day cultivars, temperature and photoperiod can strongly influence whether flower buds form.
Once fruits are developing, temperature affects:
- development rate,
- berry mass,
- sugar accumulation,
- acidity,
- color,
- and harvest timing.
A greenhouse strategy therefore needs to follow crop development rather than apply one temperature setpoint from transplant to final harvest.
VPD Is Important — But the Old Strawberry Rules Were Too Simple
The old version of this article assigned precise VPD ranges to different strawberry growth stages, such as:
0.8–1.3 kPa
for young plants and:
1.2–1.8 kPa
during flowering.
Current research does not justify presenting these as universal strawberry requirements.
VPD is certainly useful.
It describes atmospheric water demand and is more informative than relative humidity alone.
But strawberry response depends on:
- air temperature,
- leaf temperature,
- root-zone moisture,
- radiation,
- airflow,
- cultivar,
- and developmental stage.
There is no scientifically established rule that one particular VPD always produces the highest strawberry yield.
New Research Shows That VPD Can Affect Strawberry Pollination
A 2025 study directly investigated strawberry flower responses to VPD.
Researchers exposed strawberry flowers at 25°C to:
0.33 kPa
1.58 kPa
and:
2.06 kPa VPD.
All treatments eventually resulted in complete anther dehiscence, but the timing differed dramatically.
Anthers fully opened after approximately:
120 minutes at 2.06 kPa
140 minutes at 1.58 kPa
and:
270 minutes at 0.33 kPa.
The highest VPD also promoted earlier pollen release and greater pollen-clump ejection.
This directly challenges the simplistic idea that:
higher VPD during flowering is automatically harmful.
For pollen release itself, a relatively high VPD actually accelerated anther opening under the experimental conditions.
But 2.06 kPa Is Not a Recommended Greenhouse VPD
This distinction is critical.
The 2025 study investigated individual flowers and pollination mechanics.
It did not demonstrate that whole strawberry plants should remain at:
2.06 kPa all day.
At whole-plant scale, high VPD also increases transpiration demand.
The roots must replace the water being lost.
So the correct interpretation is:
Higher VPD can accelerate strawberry anther dehiscence, but the whole-plant water balance still determines whether that VPD is sustainable.
This is why there should not be one “magic strawberry VPD.”
Very High Humidity Can Delay Pollen Release
The same study provides a useful explanation for extremely humid flowering environments.
At:
25°C and 90% RH
corresponding to approximately:
0.33 kPa VPD,
anther dehiscence was considerably slower than under drier conditions.
The researchers concluded that higher relative humidity delayed pollen release.
This matters because successful strawberry fruit formation depends on pollinating a large proportion of the many individual pistils on each flower.
Incomplete pollination can contribute to malformed berries.
So continuously saturated greenhouse air during flowering is not automatically desirable.
Pollination Cannot Be Reduced to VPD Alone
A strawberry flower contains many pistils.
For good fruit shape, a large proportion must be successfully fertilized.
Environmental conditions influence pollen release, but actual pollination also depends on:
- insect activity,
- flower vibration,
- pollen availability,
- cultivar,
- stigma receptivity,
- and greenhouse management.
Therefore malformed berries should not immediately be diagnosed as:
“the VPD was wrong.”
Check pollination itself.
The 2025 research showed that mechanical vibration could substantially increase pollen movement and attachment under controlled conditions.
VPD Is Also a Water-Demand Measurement
For the whole plant, one of VPD’s most important roles is predicting transpiration demand.
A recent greenhouse strawberry study developed transpiration models using:
- solar radiation,
- VPD,
- leaf area,
- and irrigation treatment.
Including VPD substantially improved prediction of plant transpiration in soilless strawberries.
This gives VPD a very practical purpose:
it helps growers understand how rapidly the crop may be using water.
That is much more useful than treating VPD simply as a flowering setpoint.
Root-Zone Water Determines How Strawberry Plants Respond to VPD
Strawberries have relatively shallow root systems and are sensitive to water supply.
Research comparing strawberry cultivars under different water availability shows substantial differences in:
- water consumption,
- water-use efficiency,
- plant growth,
- and yield loss under water deficit.
This means the same greenhouse VPD can produce different physiological responses depending on:
- irrigation frequency,
- substrate water content,
- root-zone EC,
- root activity,
- and cultivar.
A VPD value without root-zone information is incomplete.
High VPD Does Not Automatically Mean the Plant Is Stressed
Suppose VPD temporarily rises on a bright afternoon.
If:
- root-zone water is adequate,
- salinity is low,
- roots are healthy,
- and irrigation can meet transpiration demand,
the crop may continue functioning well.
The same VPD under dry substrate conditions may cause stomatal closure and reduced photosynthesis.
So VPD should be interpreted as:
atmospheric demand
rather than:
plant stress itself.
Likewise, Low VPD Does Not Automatically Mean “Safe”
Very humid conditions reduce atmospheric water demand.
But continuously high humidity can change:
- transpiration,
- pollen release,
- disease risk,
- and fruit-surface moisture conditions.
Recent strawberry research on water-soaking disorders also shows that high water-vapor exposure and surface wetness can contribute to fruit skin disorders in susceptible genotypes.
So humidity management is a balance, not a race toward the lowest possible VPD.
CO₂, Temperature and VPD Must Be Interpreted Together
Consider three examples.
Situation 1: Strong light, low CO₂
The canopy is photosynthesizing rapidly.
If greenhouse CO₂ falls, carbon supply can limit further photosynthesis.
CO₂ enrichment may help.
Situation 2: Strong light, high temperature and high VPD
There may be plenty of photons and CO₂.
But if plant water demand exceeds root supply, stomatal conductance can decline.
The crop may not fully use the available light or CO₂.
Situation 3: Elevated CO₂ but unsuitable flowering temperature
More carbon is available.
But if flower induction or reproductive development is negatively affected by temperature, the higher CO₂ concentration may not translate into higher marketable yield.
That is why these measurements should be viewed as a system.
A Research-Based Strawberry Climate Reference
The following values come from actual strawberry experiments.
They are research conditions — not one combined optimum recipe.
| Research question | Conditions | What the study showed |
|---|---|---|
| CO₂ enrichment | ~400 vs 800 ppm | 800 ppm increased marketable yield by ~20–31% in ‘Sagahonoka’ |
| Crop-local CO₂ | +100–200 ppm near canopy | ~22% higher marketable yield with lower fuel use |
| Everbearing temperature | 15/7 to 27/19°C | Cultivar-specific yield optima ~17.9–22.7°C |
| Short-day flowering | 12–27°C day; 6–12°C night | Temperature and photoperiod strongly affected flower emergence |
| Fruit quality | 18/12 to 30/22°C | Higher temperatures reduced several fruit-quality traits |
| Flower VPD | 0.33, 1.58, 2.06 kPa | Higher VPD accelerated anther dehiscence and pollen release |
| Greenhouse transpiration | Radiation + VPD + LAI | VPD helped predict strawberry water use |
These values should not be combined into:
800 ppm CO₂ + 20°C + 1.58 kPa VPD = perfect strawberry production.
No experiment has established that formula.
A Better Greenhouse Strawberry Monitoring Strategy
1. Separate light management from climate management
Use the dedicated AquaHorti Strawberry Light Requirements guide for PPFD and DLI.
For this workflow, ask whether temperature, CO₂ and water relations are allowing the crop to use the available light.
2. Measure CO₂ at canopy level
Measure during periods of active photosynthesis.
A high reading near the greenhouse controller does not guarantee the same concentration inside the crop canopy.
3. Record day and night temperature separately
Do not rely only on average temperature.
Flower induction, flowering speed and berry development can respond differently to day and night conditions.
4. Identify the cultivar type
Short-day strawberries and everbearing/day-neutral strawberries can have different photoperiod and temperature responses.
Environmental advice should always be interpreted in that context.
5. Monitor VPD together with root-zone moisture
Use VPD to understand atmospheric water demand.
Compare it with:
- substrate moisture,
- irrigation timing,
- EC,
- root-zone temperature,
- and crop transpiration.
6. Pay special attention during flowering
Extremely humid air can delay anther dehiscence.
But pushing VPD high all day is not the solution.
Evaluate:
- pollen release,
- pollinator activity,
- fruit shape,
- temperature,
- and whole-plant water status together.
7. Record fruit quality, not only yield
Environmental treatments can alter:
- berry size,
- Brix,
- sugars,
- acidity,
- vitamin C,
- color,
- and harvest timing.
Maximum yield and maximum fruit quality are not always produced by exactly the same environment.
Sensor Placement Matters
A strawberry greenhouse can contain substantial microclimate variation.
Upper and lower cultivation layers may experience different:
- light,
- substrate moisture,
- root temperature,
- EC,
- and photosynthetic performance.
A 2026 soilless greenhouse study found that cultivation height and architecture changed both canopy and root-zone environments, producing different yield and quality outcomes.
So one central sensor should not automatically be assumed to describe every row or cultivation level.
Measure where the crop actually grows.
Why Logging Is Better Than One Reading
Strawberry climate changes through the day.
Morning conditions may be cool and humid.
Around midday:
- radiation rises,
- temperature increases,
- VPD increases,
- CO₂ demand increases.
Later, ventilation may open and CO₂ enrichment may become difficult to maintain.
A single measurement misses this pattern.
Logging temperature, humidity/VPD and CO₂ over time makes it possible to identify when a limitation occurs.
This is particularly valuable when comparing environmental records with:
- flower opening,
- fruit set,
- malformed fruit,
- berry growth,
- and harvest quality.
What Should Growers Actually Optimize?
Current strawberry research supports several strong principles.
Do not manage CO₂ independently of temperature.
CO₂ enrichment can increase strawberry yield substantially, but reproductive temperature remains critical.
Do not assume one temperature fits every strawberry cultivar.
Recent everbearing research shows cultivar-specific optimum temperatures.
Do not treat VPD as a universal stage-by-stage target.
Use it primarily to understand atmospheric water demand and flowering microclimate.
Do not assume very high humidity is always best during flowering.
Strawberry-specific experiments show that low VPD can substantially delay pollen release.
Do not diagnose malformed fruit from climate data alone.
Pollination itself must be considered.
Measure canopy CO₂ and root-zone conditions.
The plant experiences both the atmosphere and the substrate.
Key Takeaway
Greenhouse strawberry production is not controlled by one perfect combination of CO₂ and VPD.
Direct research shows that increasing CO₂ from approximately 400 to 800 ppm can increase marketable strawberry yield by around 20–31% under suitable conditions.
But newer temperature research shows that optimum yield temperature varies substantially among cultivars, with six everbearing cultivars showing estimated optima between approximately 17.9 and 22.7°C.
And 2025 strawberry-flower research shows that higher VPD accelerated anther dehiscence and pollen release, while very humid, low-VPD conditions delayed pollen release.
So the correct lesson is not:
“Keep strawberries at one fixed CO₂ concentration and VPD.”
It is:
measure canopy CO₂, track day and night temperature, interpret VPD together with root-zone water, monitor pollination, and evaluate yield and fruit quality separately.
That is a much stronger scientific basis for greenhouse strawberry management.
References
Effects of CO₂ Enrichment on Yield, Photosynthetic Rate, Translocation and Distribution of Photoassimilates in Strawberry ‘Sagahonoka’. Agronomy, 2022.
Crop-local CO₂ enrichment improves strawberry yield and fuel use efficiency in protected cultivations. Scientia Horticulturae, 2022.
Lee, H. et al. (2025). Vapor pressure deficit control and mechanical vibration techniques to induce self-pollination in strawberry flowers. Plant Methods, 21, 28.
Cardinal temperature optima for yield and berry mass in six everbearing strawberry cultivars under controlled environments. Scientia Horticulturae, 2026.
Sønsteby, A. & Heide, O. M. Influences of day and night temperatures on flowering of Fragaria × ananassa at different photoperiods. Scientia Horticulturae.
Temperatures after bloom affect plant growth and fruit quality of strawberry. Scientia Horticulturae.
Development of a strawberry transpiration model based on a simplified Penman–Monteith model under different irrigation regimes. Horticulture, Environment, and Biotechnology.