Leaf Surface Temperature

Understanding Leaf Surface Temperature and Its Impact on Plant Health 

Leaf surface temperature refers to the actual temperature on the outer surface of a plant's leaf. 

While some might think the ambient room or leaf surface temperature are the same, it's important to understand that leaf temperature is influenced by a number of factors. Factors such as light intensity, air movement (or lack of air movement), humidity levels, and even the plant’s own transpiration rate can cause the leaf temperature to be significantly different from the surrounding room temperature.

Why Leaf Temperature Matters 

Leaf temperature plays a critical role in a plant’s internal processes (photosynthesis and transpiration). When a leaf gets too hot (or too cold), these processes can be disrupted.  

An example of this is when the leaf temperature is too warm. Overheating can cause a plant to close its stomata (the tiny pores on the leaf surface) which reduces its ability to take in Carbon Dioxide, which is essential for photosynthesis. Similarly, under cold conditions, the internal enzymatic process slows down which leads to limited energy production and growth. 

Think of it like the human body: when we overheat, we sweat to cool down; when we get cold our body will shiver to generate heat. Plants also have mechanisms to regulate their internal / external states, but they’re highly dependent on environmental conditions to help them function correctly. 

Measuring Leaf Temperature 

The best way to measure the surface temperature of a leaf is by using an infrared temperature gun. This tool allows for a ‘live’ temperature reading directly from the leaf surface.  

*Some commercial and advanced growers even monitor the leaf temperature by using thermal cameras or they use automated systems that can collect readings with specialised sensors that allow for continued data tracking.  

Ideal Leaf Surface Temperature Range 

While not the case for all plants, some plants thrive when their leaf surface temperature is about 1–2°C below the ambient temperature. This typically falls within the range of 25°C to 30°C (depending on the plant species and stage of growth). 

However, it's worth noting that this is just a guideline. Each plant species—and even different growth phases within the same species—will have specific temperature needs.

The Role of VPD (Vapour Pressure Deficit) 

VPD (vapour pressure deficit) measures the difference between the amount of moisture in the air and how much moisture the air could hold when 'fully saturated'. 

Lower VPD values (typically between 0.5–1.0 kPa) indicate a more humid environment and result in low transpiration stress. However, leaf temperatures tend to be higher under these conditions. 

Higher VPD values (typically between 1.0–1.5 kPa) suggest a drier atmosphere, which can lead to higher transpiration rates and lower leaf surface temperatures, but also potentially higher stress if not properly managed. 

Understanding and controlling leaf surface temperature can significantly enhance plant health, resilience, and productivity. 

If you would like to learn more about VPD follow this guide: HERE