Posted on by Alex Russell

Leaf Surface Temperature

Good gardeners, especially those growing indoors, will always track the temperature of their growing environments to help maintain optimal growing conditions, but very few gardeners are monitoring their leaf surface temperatures. In this tutorial we're going to have a look into Leaf Surface Temperature (LST) and how they effect your plant.


Why does leaf surface temperature matter and why should gardeners look into measuring this?

Leaf Surface Temperature (LST) helps determine the actual temperature of the plant, which is different to the ambient temperature of your growing environment, although the environmental temperature will also play a role in the temperature of your plant.

In most plants, leaves play a key role in a plants metabolism, if a plant's leaves are at an optimal temperature, the plant will reach its maximum potential for growth through temperature alone, but obviously there is many other factors that will determine a plants true potential for growth overall. Most educated and experienced growers are always looking for ways to optimize their gardens for that perfect grow, as environmental conditions and temperatures play a big role in the success or failure of plants growth.


How to measure your Leaf Surface Temperatures

FLIR Thermo ImagingMeasuring your LST can be effectively achieved with tools such as FLIR Cameras or Infrared Thermal Imaging cameras or meters. The most accurate way to measure LST would be using a FLIR Thermal Camera, as the surface temperatures can vary across surfaces of each leaf, this would allow you to see the true temperature variance of each leaf. A FLIR Thermal Camera can be quite a costly investment and usually out of the price range of the hobbyist grower.

Infrared ThermometerA cheaper alternative to measure your LST is by using a Infrared Thermometer, although this will only measure temperatures at a single point. When taking measurements of temperature using an Infrared Thermometer, it may be worth reading several points per leaf to get a better idea of the surface temperature. An Infrared Thermometer can usually be found at a reasonable price for the hobbyist grower and can be a very useful tool for checking other temperature points of your environment and reservoirs.


What is the optimal Leaf Surface Temperature?

Unfortunately this is not an easy question to answer, as there is too many additional variables that play a part in this. Many factors, such as: plant type, concentrations of CO2, strains variations, etc. all factor in determining the exact optimal LST.

For many plants, the leaf temperature range for photosynthesis would be between 15c celsius and 30c celsius (59F - 86F) on average with normal atmospheric concentrations of CO2, this range would increase as the levels of CO2 increased within the environment.

Studies have shown that when growing using LED horticultural lights, leaf surface temperature (LST) is lower than using traditional HID lighting, usually resulting in the LST being lower than optimal under LED lights. 

Many growers who supplement CO2 into their grow rooms are also intentionally raising their overall environmental temperature to increase their CO2 absorption by their plants. As a by-product of increasing the environmental temperature of the grow space, the overall LST of the plant will also increase, which is common practice by commercial growers utilizing LED lights in certain colder climate regions.