How to adjust the VPD in indoor cultivation in stages
The VPD in indoor cultivation It is a very useful reference to know if the environment allows plants to transpire in a balanced way. It's not just about looking at relative humidity or temperature separately, but understanding how they work together. Two rooms with the same 60% humidity can have very different behaviors if one is at 22 ºC and the other at 28 ºC.
When the VPD is in range, the plant can move water and nutrients with more stability. When it is too low, the environment becomes stuffy, perspiration slows down and the risk of condensation increases. When it is too high, the air pulls on the plant too much, the substrate dries out sooner and symptoms may appear that are confused with deficiencies, blockages or excess watering.
To control it well you need three things: measure temperature and humidity accurately, know the approximate range of each stage and have tools to correct the environment. At Grow Industry you can find equipment designed for this work, such as the Temperature, Relative Humidity and Dew Point Meter, the CLIVEX Humidity and Temperature Controller, the Humidifier 8L/day PURE FACTORY and the Dehumidifier 12L/day EDM.
What is VPD and why does it matter indoors?
VPD means vapor pressure deficit. Simply put, it indicates the difference between the humidity that the air contains and the humidity it could contain before becoming saturated. The greater this difference, the more capacity the air has to extract moisture from the leaves. The lower it is, the less force the environment has to promote perspiration.
Indoors, this reference is especially practical because the grower controls almost everything: lighting, extraction, ventilation, temperature, humidity, irrigation and plant density. Therefore, when working with a closet or closed room, it is not enough to say that a humidity of 60% is good or bad. It depends on the actual temperature of the crop and, if you want to refine it further, on the temperature of the leaf.
A correct VPD helps the plant maintain stable transpiration. This transpiration not only affects the water lost by the plant, it also influences the movement of nutrients from the roots to the aerial part. If the environment is out of range for many hours, the crop may respond with drooping leaves, dry edges, slow growth, excess moisture in flowers or irregular water consumption.
Recommended ranges according to stage
The ranges should not be understood as a rigid rule. Each variety, growing system, light output, pot size and watering strategy may require minor adjustments. Even so, these values are a practical basis for starting to work on the climate judiciously.
| Stage | indicative VPD | Searched environment | Priority |
|---|---|---|---|
| Seedlings and cuttings | 0.6 - 1.0 kPa | Higher humidity and soft demand | Avoid dehydration |
| Growth | 0.8 - 1.2 kPa | Stress-free active perspiration | Stable vegetative development |
| Pre-flowering | 1.0 - 1.3kPa | Less humidity and good renewal | Prepare floral structure |
| advanced flowering | 1.2 - 1.5 kPa | Drier and controlled environment | Reduce risk of excessive humidity |
For seedlings and cuttings, it is advisable to avoid too dry air. Young plants have few roots and less capacity to compensate for rapid water losses. Therefore, in this phase, a higher relative humidity and a moderate temperature are usually of interest, without direct currents that accelerate dehydration.
In growth, the plant can already work with a somewhat more active environment. The goal here is for it to drink and sweat regularly, without the substrate drying out too quickly or always remaining wet. A good balance in this phase helps to form a strong structure before moving on to flowering.
During flowering, especially when the plant mass and density of the flowers increase, it is important to progressively lower the humidity. It does not mean drying the crop suddenly, but rather preventing the environment from becoming saturated at night or in areas with little air circulation. At this stage, controlling the climate is as important as watering well.
How to measure temperature, humidity and dew point
The first common mistake is adjusting the weather with unreliable readings. A cheap hygrometer that is poorly placed can show humidity that does not represent what happens at the height of the tips. There may also be important differences between the upper area of the closet, the center of the plant mass and the lower part, especially if the internal ventilation does not distribute the air well.
The Temperature, Relative Humidity and Dew Point Meter It is an interesting tool when you want to go beyond the basic humidity reading. It measures temperature, relative humidity and dew point, which helps detect condensation situations before they become a problem. In dense crops, drying rooms or curing areas, this information can make a difference.
Meter placement matters. It is advisable to measure at the height of the canopy, close to the plants, but without placing the sensor attached to a wet leaf, in front of the direct outlet of a humidifier or just below a strong extraction current. If the sensor receives a direct influence, the reading will be useful for that specific point, but not to understand the general climate of the crop.
Adjust the climate by raising or lowering humidity
When VPD is high, the air is typically too dry for the current temperature. In that case, the plant transpires more than necessary and may respond by closing stomata to protect itself. The result can be slower growth, tired-looking leaves, and water consumption that is difficult to control.
The most direct solution is usually to increase the relative humidity. For that, a team like Humidifier 8L/day PURE FACTORY It allows cold steam to be provided without increasing the ambient temperature. Its 8-liter tank and output regulation make it easy to adjust the supply according to the size of the space and the real demand of the crop.
When the VPD is low, the opposite occurs: the air is too close to saturation. The plant transpires little, water takes longer to move and the environment can favor condensation on cold surfaces or areas with poor ventilation. During flowering, this scenario should be corrected quickly, especially during the hours of darkness.
To reduce humidity, the Dehumidifier 12L/day EDM It can help in small or medium spaces. It is a compact device, with an extraction capacity of up to 12 liters per day in optimal conditions, a 2.1 liter tank and an air flow of 100 m³/h. In indoor cultivation, this type of equipment is useful when extraction is not enough to control humidity peaks.
Temperature: the setting that changes everything
Relative humidity does not behave the same at different temperatures. If the temperature rises and the amount of water vapor in the air does not change, the relative humidity can drop. If the temperature drops, the relative humidity can rise and approach the dew point. That's why many rooms look fine with the light on, but become humid when the light is turned off.
This point is key for VPD in indoor cultivation. You can have an acceptable reading during the day and go completely out of range at night. In LED, in addition, by emitting less radiant heat than other systems, some rooms work with lower leaf temperatures, which can modify the actual reading experienced by the plant.
If you need to raise the VPD, you can slightly increase the temperature or lower the humidity. If you need to lower it, you can reduce the temperature or increase the humidity. The safest thing is not to make sudden changes: adjust little by little, measure for several hours and check how the plant responds before continuing to correct.
Automatic control with humidity and temperature
Controlling the environment manually works for small crops, but requires checking the closet many times a day. In addition, the most problematic changes usually occur when you are not in front: when the lights go out, when the extraction is turned on, after abundant watering or on days with very humid outside weather.
The CLIVEX Humidity and Temperature Controller allows you to automate part of that work. It can manage humidity between 20% and 95% RH and temperature between -10 ºC and 40 ºC. It also includes humidification, dehumidification, heat and cool modes, with start and stop settings. This allows you to connect a humidifier or dehumidifier and keep the climate within a more stable window.
The key is to set realistic ranges. If the range between on and off is too narrow, connected equipment may wake up constantly. If the margin is too wide, the crop will spend many hours off target. In practice, it is advisable to work with a small hysteresis: for example, activate the humidifier when the humidity drops below a certain point and turn it off a few points above.
Quick fix table
| Reading | What does it usually indicate? | Recommended action | Useful product |
|---|---|---|---|
| High VPD | Dry air or high temperature | Increase humidity or lower temperature | PURE FACTORY Humidifier |
| low VPD | Excess humidity or low temperature | Lower humidity or raise temperature | EDM Dehumidifier |
| Nighttime humidity spikes | Temperature drop with lights off | Schedule night dehumidification | CLIVEX Controller |
| Unstable readings | Poorly placed sensor or poorly distributed air | Measure at canopy height and improve ventilation | PROSKIT meter |
Common mistakes when working with VPD
Just look at the relative humidity
Relative humidity alone doesn't tell the whole story. 65% may be adequate in an early phase with moderate temperature, but excessive in advanced flowering if the temperature drops at night. The useful data appears when you relate humidity and temperature.
Do not measure where the plants are
Measuring on the closet wall, on the floor, or next to the exhaust may give a different reading than what the plant receives. To properly adjust the VPD in indoor cultivation, take the canopy area as a reference and check different points if the space is large or heavily loaded.
Correct too quickly
Going from a humid environment to a very dry one in a few hours can stress the crop. The same thing happens if the humidity is raised without checking the ventilation. The ideal is to make gradual changes, especially between stages.
forget the night
With lights off, the temperature drops, the relative humidity rises and the balance of the environment changes. Many condensation problems appear during these hours, even if during the day everything seems fine. A controller with alarms or automation helps avoid these spikes.
Practical configuration by stage
Seedlings and cuttings
In this phase, a soft environment is of interest. The plant does not yet have a powerful root, so it is not advisable to force intense transpiration. Maintain higher humidity, avoid direct air and measure frequently. If the environment becomes too dry, a humidifier with adjustable output allows stability to be restored without heating the room.
Vegetative growth
During growth, the plant can already work with a higher demand. Balance is sought here: enough transpiration to move water and nutrients, but without the substrate drying out at excessive speed. A medium range helps maintain uniform development and reduces sudden changes between waterings.
Pre-flowering
In pre-flowering it is advisable to start lowering humidity little by little. The plant increases in volume, spaces between branches close and internal circulation may worsen. It is a good time to review fans, extraction and measurement in different areas of the crop.
advanced flowering
In advanced flowering the priority is to avoid accumulated humidity. Dense flowers retain more moisture and any spot with stagnant air can become a problem. Working with a somewhat drier environment, without going to extremes, helps keep the crop safer.
Recommended products to control the environment
To measure accurately, the Temperature, Relative Humidity and Dew Point Meter It is a professional option for those who want to check more than basic humidity. By including dew point, it helps interpret the risk of condensation in growing, drying or curing rooms.
To automate, the CLIVEX Humidity and Temperature Controller It is a simple solution to activate equipment according to configured values. It can work with humidification, dehumidification, heat and cold, so it fits well in rooms where the climate changes between day and night.
To increase humidity, the Humidifier 8L/day PURE FACTORY provides cold steam using ultrasonic technology. It is useful in early stages, in dry rooms or when heating and extraction reduce ambient humidity too much.
To lower humidity, the Dehumidifier 12L/day EDM helps remove water from the air in spaces of 15 to 20 m². It is especially practical in flowering, after abundant watering or in rooms where outdoor humidity complicates climate control.
You can also review the categories of humidifiers, dehumidifiers, environmental controllers and temperature and humidity meters to adapt the equipment to the real size of your crop.
How to create a weekly check-in routine
A good routine avoids late correction. Note temperature, humidity and behavior of plants during various times of the day: beginning of lights, middle of the photoperiod, end of lights and first hours of darkness. With this data you will see if the problem always appears in the same period.
If he VPD in indoor cultivation it goes out of control only with the lights off, prioritize night management: more extraction, programmed dehumidification or a more stable minimum temperature. If it gets out of control with the lights on, check the light output, distance from the plants, internal ventilation and humidity supply.
After each watering, check how the humidity rises. In crops with many plants, the environment can be loaded quickly by evaporation of the substrate and transpiration. If the spike lasts only a short time, it may be normal. If it remains for hours, you need to improve extraction, dehumidification or air movement.
VPD FAQ
What VPD is recommended in seedlings or cuttings?
For seedlings or cuttings, a low VPD is usually used, approximately between 0.6 and 1.0 kPa. The idea is to reduce the demand for transpiration so that the young plant does not dehydrate before developing a strong root.
How do I lower the VPD if it is too high?
To lower it, you can increase the relative humidity with a humidifier, reduce the temperature or combine both settings. In small spaces, it is usually most practical to use an adjustable humidifier and measure at the height of the canopy.
How do I raise the VPD if it is too low?
To increase it, you can lower the humidity with a dehumidifier, slightly increase the temperature or improve air renewal. In flowering, it is usually safer to correct excess moisture before it accumulates overnight.
Is an automatic controller necessary?
It is not mandatory, but it makes the work much easier. A controller allows the humidifier or dehumidifier to be activated according to the configured values, preventing the crop from depending on constant manual adjustments.
Can I use only one VPD table?
A table helps, but is not a substitute for actual measurement. The table guides you, but each room has variations due to ventilation, light output, plant density and leaf temperature. The ideal is to use a table, meter and observation of the plant.
