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Greenhouse tomato cultivation has become one of the most efficient methods. This farming method provides several unique advantages for growers because the greenhouse structure allows farmers to regulate environmental conditions. Adjusting and maintaining ideal temperature, humidity, light and CO2 levels creates a stable tomato grow throughout the year. Thereby, growers can achieve higher yields, better fruit quality, and more consistent production compared to open field growers.
Tomatoes are one of the most widely cultivated vegetable crops in the world due to many reasons, including their taste, colour, high nutritional value and versatility. Additionally, tomatoes can be consumed in many ways. They are consumed as fresh fruits, partially cooked, or processed into sauces, pastes, and juices. Furthermore, tomatoes as a source of essential nutrients for human health. Tomatoes contain carotenoids, flavonoids, minerals, vitamins, and phytosterols. Â
The main environmental factors affecting greenhouse tomato cultivation are,Â
- Temperature
- Relative Humidity
- Vapour Pressure Deficit (VPD)
- CO2 Level
Proper management of these factors can achieve a maximum tomato yield with a minimum energy input.
Ideal Temperature Range for Greenhouse Tomatoes
Temperature is one of the most critical environmental factors in greenhouse tomato cultivation. Tomato plants require specific temperature conditions at each growth stage. These ideal temperatures for growing tomatoes should be maintained to keep the plants healthy and stress-free. In fact, from seed germination to flowering and fruit development, a correct temperature range must be maintained for tomato plants. It ensures :Â
- Strong vegetative growth
- Healthy floweringÂ
- Proper pollinationÂ
- Good fruit set
If the temperature falls below or rises above the optimal level, tomato plants can face stress conditions. That can lead to poor growth, low fruit set, and reduced yield.
Daytime temperature
Research findings continuously show that tomato crops perform best in warm and steady conditions. During the daytime, the ideal tomato growing temperature is between 21–27°C (70–82°F). This temperature range supports healthy vegetative growth and successful pollination.
Night-time temperature
At night, tomatoes prefer cooler conditions, usually around 16–18°C (62–64°F). This temperature range helps the tomato plants to balance respiration and supports normal physiological processes.
The optimal Temperature for Germination and Planting
At the start of tomato cultivation, care should be taken to regulate the temperature for maximum seed germination. The optimum temperature for planting tomatoes is between 18 and 29°C (65 and 85°F). This ensures successful germination. Within this range, seeds sprout quickly and uniformly, which is essential for commercial propagation and greenhouse production.Â
Day time | Night time | Seed germination |
21-27 °C (70-82°F) | 16-18 °C (62-64 F) | 18-29 °C ( 65-85°F) |
Table 01: Ideal Temperature Summary for Tomato Cultivation
How to Maintain Ideal Temperature in a Tomato Greenhouse
Temperature control is essential for greenhouse tomatoes. There are several methods to control and regulate ideal temperatures inside tomato greenhouses, such as insulating and using specialised equipment. Dedicated HVAC (Heating, Ventilation, and Air Conditioning) systems are ideal equipment for this purpose. Farmers can set the desired levels, and the system will automatically adjust to fit those conditions. Additionally, properly insulating the greenhouse will make the temperature control efficient and reduce energy wastage. Insulating prevents heat loss during cooler periods and keeps daytime and nighttime temperatures stable for tomato growth.
Greenhouse Humidity Levels for Tomato Growth
Another critical environmental factor for growing tomatoes is the relative humidity (RH). It directly affects plant growth and development, yield, and fruit set. There are several factors contributing to the total humidity inside the greenhouse. They are:Â
- Plant transpiration
- Soil evaporation
- Ventilation
- Condensation on the greenhouse covering.
According to research findings, the ideal relative humidity range is between 60–85% for most greenhouse tomato varieties. However, many researchers suggest that maintaining 50–70% RH throughout the growth cycle leads to better plant health, stronger flowering, and improved fruit development. Generally, when the humidity level is above these levels, plants are unable to release the water vapour through their stomata. This inhibits the ability of tomato plants to absorb water and other necessary nutrients from the soil and will ultimately hinder plant development. On the other hand, low humidity levels can cause plant stress. This is caused due to the stomata being closed to retain the remaining water from evaporating.
Another important thing is that relative humidity should be set to different levels during daytime and nighttime.
Day-time humidity level
During the day, tomato plants are actively engaging in photosynthesis and transpiration. Therefore, the ideal relative humidity (RH) in a tomato greenhouse during the daytime should be between 55-70%.Â
Maintaining RH in this range ensures the following:
- Optimise water movement from roots to leaves
- Support healthy vegetative growth
- Promote proper flower and fruit development
- Reduce the risk of tomatoes experiencing low or high humidity, which can cause stressÂ
Extreme humidity levels during the daytime can destroy the tomato crops and lead to diseases. In particular, high daytime RH (above 75%) can slow transpiration and increase the risk of fungal diseases, while very low RH can lead to water stress and reduced fruit quality.
Night-time humidity level
At night, tomato plants are less active, and a slightly higher RH of 65–75% is recommended. Maintaining the RH in this range at night is necessary to:
- Prevent excessive water loss from leaves
- Maintain turgor in stems and fruits
- Reduce plant stress during cooler nighttime temperatures
However, high RH at night may cause condensation and favour disease and mildew development. These also include harmful fungal diseases such as botrytis and powdery mildew. Maintaining the proper humidity level is necessary to protect against diseases and reduce crop loss.Â
During Pollination
Special care should be taken when the tomato plants enter their pollination period. Many experiments and research have been conducted to find the ideal humidity during pollination, and they suggest this value to be around 70%.Â
How to maintain ideal humidity in a tomato greenhouse
Efficient and reliable equipment should be selected to maintain humidity at precise levels. For this purpose, greenhouse tomato farmers primarily use two equipment. One method is to use a dehumidifier, and the other is to use an HVAC (Heating, Ventilation, and Air Conditioning) system. Dehumidifiers like Co-Airo 200 are known to use state-of-the-art heat exchangers to remove excess moisture from the air efficiently. They are primarily designed to dehumidify greenhouses, and many farmers use Co-Airo 200Â because these dehumidifiers are easy to set up and cover a wide area. On the other hand, the primary purpose of HVAC systems is not to regulate humidity, but to control the temperature. Although HVAC systems can reduce the humidity as a side effect, they are incapable of regulating the humidity at precise levels. Therefore, many tomato farmers resort to using dedicated dehumidifiers to regulate the humidity inside their greenhouses. Dehumidifiers are known to improve tomato growth and quality, and also reduce disease risks and energy costs, often by up to 50%.
Vapour Pressure Deficit (VPD) and Tomato Growth
Vapour Pressure Deficit (VPD) measures the difference between the air’s moisture-holding capacity and the actual moisture content. VPD has a direct connection with the relative humidity level inside the greenhouse. It is an important indicator of how greenhouse tomatoes experience water stress because it combines the effects of both temperature and humidity.
       High Vapour Pressure Deficit (VPD)
- Rapid transpiration
- Risk of leaf water stress
- Reduced nutrient uptake
Low Vapour Pressure Deficit (VPD)
- Slow transpirationÂ
- Condensation and a higher risk of fungal diseases
An optimal VPD level must be guaranteed to combat the negative effects of extreme VPD levels. Maintaining the optimal VPD ensures proper plant health while minimising stress and diseases.Â
Current research suggests that the ideal VPD level for growing tomatoes lies between 0.5-0.8 kPa. This VPD level should be maintained until the flowering stage and can be increased up to 1.2 kPa after reaching it.Â
| Growth Condition | Recommended Range |
| Day-time relative humidity | 55-70 RH % |
| Night-time relative humidity | 65-75% RH% |
| Optimal RH for Pollination | Around 70% |
| Ideal Vapour Pressure Deficit (VPD) | 0.5- 1.2 kPa |
 Table 02: Ideal Relative Humidity & VPD for Tomato Cultivation
CO2 levels and their Impact on Growth
Carbon dioxide (CO2) is the most essential factor that helps tomato plants in photosynthesis. It aids tomato plants in converting light, water, and nutrients into energy. Therefore, to maximise the efficiency of photosynthesis and increase the tomato yield, optimal CO2 levels should be maintained inside the greenhouse.Â
Growing Conditions | Recommended CO2 Levels (ppm) |
|---|---|
Sunny days | 800- 1000Â |
Cloudy or low-light days | 400- 600Â |
Seedlings after establishment | 800- 1000 |
Maximum safe level | Below 5,000 |
Table 03: Recommended CO2 Levels ( Levels above 5,000 ppm can harm plants and pose a safety risk for workers)
Several steps can be taken to maintain the ideal CO2 levels for growing tomatoes. One cost-efficient method is to burn fuel such as propane, natural gas and kerosene. Although harmful for the environment, it is one of the most inexpensive methods to control CO2 levels. Another method is to place Liquid CO2 tanks inside the greenhouse. Using organic CO2 sources like manure and compost is environmentally friendly.
Conclusion
Proper environmental conditions should be maintained for tomato cultivation inside greenhouses. Factors such as temperature, humidity and CO2 levels should be set to optimal levels to guarantee the best growing conditions. These factors can be controlled by using specialized equipment, and care should be taken to follow the guidelines set by researchers. By following the best practices mentioned in this guide, greenhouse tomato farmers can achieve consistent fruit growth, reduced plant stress, fewer diseases and high-quality yields.
