Tomatoes - Climate Analysis

How can the environment effect Tomato growth


How can the growing Environment effect crop growth and health?


Temperature is an important environmental feature that can affect tomato plants development in different ways and through different stages of plant growth. This includes development, including growth, photosynthesis, respiration, nutrient deficiencies and physiological development.

In general, the optimal daytime temperature for tomato production is in the range of 21 to 27°C, and optimal nighttime temperatures are between 17 and 18°C. However, optimal temperatures vary somewhat with the growth stage of the plant. Nutrient deficiency symptoms, primarily from the lack of taking up phosphorus, start to appear at temperatures below 16°C. At temperatures above 30°C lycopene, the red pigment in tomatoes, does not form and fruit do not color properly. (Temperature, Humidity, and Water in Protected Culture Tomatoes )

Extreme high and extreme low temperatures can have significant effects on tomato crops. When temperatures are too high, it can result in heat stress for the plants. This can lead to reduced photosynthesis, wilting, and even plant death. High temperatures can also affect the pollination process, as it can cause the pollen grains to become sticky and less likely to disperse, resulting in lower pollination rates and reduced fruit set.

Cold temperatures can slow down plant growth and development, as well as inhibit nutrient uptake. It can increase the risk of frost damage, which can cause wilting, discoloration, and even death of the plants. Additionally, low temperatures can negatively impact fruit development and ripening, resulting in smaller and less flavorful tomatoes.


Temperature also affects relative humidity in that warm air can hold more water than cool air, and relative humidity is expressed as a percentage of the maximum amount of water that the air can hold. Understanding the effects of temperature is necessary to optimize the production of tomatoes in protected culture systems.

Production guides for greenhouse tomatoes vary somewhat in their recommendations for optimal relative humidity (RH) levels; anywhere from 60 to 85%. Higher humidity levels can result in better fruit set, to a point, but high humidity also favors disease development.

The optimum relative humidity for pollination is 70%. At RH levels above 80%, pollen grains start to stick together, reducing their dispersal and lowering pollination rates. The stickiness of pollen goes down as humidity levels drop. At RH levels below 60%, the stigma (the female part of the flower that receives pollen) can dry out, also lowering the rates of pollination (Temperature, Humidity, and Water in Protected Culture Tomatoes )  

When humidity is too high, it creates a favorable environment for the growth of fungal pathogens and diseases. Common diseases which thrive at high humidity includes powdery mildew, leaf spot, and blight. These diseases can significantly reduce crop yields and quality. 

When humidity is too low, it can lead to reduced transpiration and water uptake by the plants. Consequently this can result in water stress and inadequate nutrient uptake, particularly calcium. Insufficient water movement through the plant can hinder overall growth and development, negatively impacting tomato crop yields.

Vapour Pressure Deficit

Vapour Pressure Deficit (VPD) is the difference between the amount of moisture in the air and the amount of moisture the air can hold when it is saturated. VPD is often used to assess the potential for water evaporation from plants, as the difference between how much moisture is in the air currently and the maximum possible (the deficit) is representative of how much water the plant can transpire.

It is an important factor to consider because it affects the movement of water through the plant and the uptake of nutrients by the root system.

If the VPD is too low transpiration is reduced because water is not evaporating from the leaf. As a result, water does not move through the plant, and some nutrients (such as calcium) are not adequately taken up by the root system.

If the VPD is too high (dry air in the greenhouse), plants can transpire a lot of water. Excessive transpiration can lead to plant stress and water loss, which can negatively impact tomato crop growth. In high VPD conditions, the plant may not be able to take up water efficiently, resulting in water stress and reduced growth.

Light (Radiation Intensity)

Light has an impact on photosynthesis, pollination, flower development, development of fruit, properties of developed fruit and overall health of the plant. 

When plants receive the right amount of light, they can efficiently convert it into energy through photosynthesis. This energy is then used to produce sugars, which are vital for plant growth and development. Adequate light levels also promote the formation of healthy and abundant flowers, which are necessary for successful pollination and fruit set.

Too much light can have negative effects on the crop. Intense sunlight can cause burns and lesions on the leaves, fruits, and stems, leading to reduced plant vigor and compromised health. These damages can also make plants more susceptible to diseases and pests.

When tomato plants are deprived of sufficient light, they may become weak and leggy, with elongated stems and sparse foliage. This can make the plants more susceptible to diseases and pests. Weak plants are also less able to withstand environmental stressors, such as temperature fluctuations or drought conditions.

Too little light can can also effect quality and yield. Without adequate light, plants may struggle to produce the sugars necessary for proper fruit formation and ripening. 

Formation of healthy and abundant flowers is also effected. Formation of healthy flowers is crucial for successful pollination and fruit set, and weaker flowers can result  in lower overall crop yields.

Day/Night Temperature Difference 

The Day/Night Temperature Difference can have a significant impact on the growth and health of tomato crops. This temperature difference refers to the variation between the daytime and nighttime temperatures experienced by the plants.

A balanced Day/Night Temperature Difference is crucial for the optimal development. When the temperature difference is too high or too low, it can lead to stress and negatively affect plant growth. Extreme temperature fluctuations can disrupt the plants' physiological processes, leading to reduced photosynthesis, nutrient deficiencies, and impaired flowering and fruit development.

Conversely, an optimal Day/Night Temperature Difference can have several benefits for tomato crops. It can stimulate strong root development, increase nutrient uptake, and enhance overall plant vigor. This balanced temperature difference also plays a role in regulating the plants' metabolism and helps them cope with environmental stressors.

Dew Events 

Dew formation can have negative effects on crop growth and health in tomatoes in a protected environment. Dew is formed when the temperature of the plant's surface is cooler than the surrounding air, causing moisture in the air to condense and form water droplets on the leaves and other plant surfaces.

The presence of moisture on the leaves and other plant surfaces can create an ideal environment for the germination and growth of fungal pathogens and other diseases. These pathogens thrive in moist conditions and can cause diseases such as powdery mildew, leaf spot, and blight. If left untreated, these diseases can significantly reduce crop yields and quality.


What actions can be taken if we do not have optimal growing conditions? 

The actions that a grower can take to combat adverse environmental conditions can vary depending on the technology the grower has available. In the section below we have collated general guidance on activities which can be taken to improve the growing conditions.

Remember to consider all of the levers you have available. These can include irrigation, cultural practices, venting, treatments, and others.

For example, if you do not have vents or an ability to cool the environment, increased irrigation may be necessary to reduce plant stress.


To mitigate the effects of extreme temperatures, growers can implement various strategies. For high temperatures, shading techniques can be used to reduce direct sunlight and lower the temperature inside the protected environment. Proper ventilation and airflow are also crucial to dissipate excess heat and maintain optimal temperature levels. This can be achieved through the use of fans or vents.

In the case of low temperatures, growers can use heating systems to maintain a suitable temperature range for the tomato plants. This can include the use of heaters or heating mats to provide supplemental warmth. 


For high humidity conditions, proper ventilation and airflow are essential to reduce excess moisture in the air and promote air circulation. This can help prevent the growth of fungal pathogens and diseases. Air circulation can be achieved with vents, or cultural methods such as pruning.

In cases of low humidity, growers can utilize methods to increase humidity levels, such as misting or fogging systems, or cultural methods like reduced pruning. 

Vapour Pressure Deficit

Managing VPD can be acheived through measures to control temperature and humidity, such as adjusting the ventilation. Maintaining the right balance of humidity can help ensure that the VPD is within the optimal range for tomato plants.

Light (Radiation Intensity)

In protected cropping systems, growers can use shading techniques to reduce the intensity of sunlight during peak hours. This helps to protect the plants from excessive radiation while still allowing them to receive sufficient light for photosynthesis. Shading can include shade cloths, white wash, or increased plastic.

Day/Night Temperature Difference 

Maintaining an appropriate Day/Night Temperature Difference can be achieved through climate control measures listed above, particularly those to manage temperature. This may involve adjusting the ventilation and cooling systems to regulate the temperature during the day, as well taking steps to prevent excessive heat loss at night.

Dew Events 

To mitigate the negative effects of dew formation, growers in protected environments can take several actions. One approach is to provide adequate ventilation and airflow within the growing area. Proper ventilation can help to reduce humidity levels and prevent moisture from accumulating on the plant surfaces. This can be achieved through the use of fans, vents, and other ventilation systems.

Another strategy is to prune the plants appropriately to allow for good air circulation. This can help to reduce the amount of time that the plant surfaces remain wet and minimize the risk of disease development. Additionally, growers can apply preventive measures such as using fungicides or applying organic treatments to protect the plants from fungal diseases.

A key management aspect is to respond quickly when dew events occur. This can be achieved by utilising temperature and humidity alerts within FarmRoad.


 How does FarmRoad calculate optimality? 


  1. Every Monday, FarmRoad looks back at the past 7 days of climate data.

  2. FarmRoad then categorises the climate data from each hour of the week  into optimal, sub-optimal or adverse for plant growth and yield based on data science and crop knowledge.

    • Optimal - best for growth and yield

    • suboptimal - not best conditions, but not threatening to plant

    • adverse / extreme - threatening to plant e.g. temperature below 5°C

  3. We do this for each climate factor including:

    1. Estimated VPD

    2. Temperature

    3. Relative Humidity

    4. Light

    5. Day and Night Temperature differences

  4. FarmRoad's Climate Analysis algorithm takes into account your farms location, crop, and season to intelligently analyse only the hours that matter.
    1. For light this means we analyse daylight hours
    2. For Day and Night Temperature difference the hours which are day or night change throughout the year.
  5. FarmRoad then calculates the proportion of time your growing environment was in each specific condition:

    • Optimal ( % and hours)

    • below optimal ( % and hours)

    • above optimal ( % and hours)

    • extreme low ( % and hours)

    • extreme high ( % and hours)

  6. FarmRoad also then calculates how many times your growing environment experienced time in which dew could form - a Dew Event.

    1. FarmRoad does this by analysing when Temperature goes below Dewpoint for a significant period. 

What does 'Optimal' mean?

FarmRoad categorises your climate data into optimal or adverse for plant growth and yield based on data science and crop knowledge.

    Extreme Low Below Optimal Optimal Above Optimal Extreme High
Humidity Day <60 60-65 65-80 80-85 >85
Night <65 65-70 70-75 75-80 >80
Temperature Day <7 7-21 21-27 27-30 >30
Night <7 7-16 16-18 18-20 >20
Radiation Summer >300 300-600 600-800 800-1000 >1000
Winter <150 150-200 200-300 300-350 >350
Day Night Temperature Difference   <2 2-3 3-5 5-7 >7
VPD   <0.5 0.5-0.8 0.8-1.1 1.1-1.5 >1.5
Dew Events   Dew Events are determined by analysing when Temperature goes below Dewpoint for a significant period.