Understanding optimum Temperature and Humidity for Plants

Ideal Temperature and Humidity for Plant Growth in Grow Rooms

It’s well recognised that temperature and humidity are two of the main environmental factors which will determine your plants growth levels and overall health. Depending on which stage of the lifecycle your plant is at, will depend on the humidity and temperature levels that you should maintain.

Temperature, Humidity and Other Important Factors

There are typically three main temperature points of plant growth. These refer to the minimal, optimal, and maximum temperature.

  • Vegetative phase – 25 degrees Celsius and 60-70% humidity.
  • Flowering phase – 28 degrees Celsius and 40-50% humidity.

The biochemical process for growth depends on temperatures being kept within ideal range for photosynthesis to occur at optimal rates. If temperatures are above or below this range, the metabolic and biochemical process will slow down, ultimately slowing down the overall development of your crop. Within your grow space, we advise that you keep on top of all growth factors such as light, Co2 levels, water, temperature and nutrition. By optimising these, you will achieve maximised results from your plants.

Links Between Temperature and Relative Humidity

Humidity refers to the amount of water vapour that can be measured in the air. Reduced humidity percentage in the air will cause water loss from your plant’s tissues. On the contrary, high humidity levels can cause microbial and fungal pathogens to develop,

In warmer temperatures, plants will close their stomata to decrease water loss and also help your plants cool off. When the temperature is too high, plants close their stomata to conserve water. If the stomata is closed, oxygen and carbon dioxide molecules cannot be moved throughout the cells, resulting in your plant suffocating on transpired gases and water vapours.

Instruments to Identify and Control Temperature in Grow Space

With the proper instruments, you can continuously collect and store the grow room temperature and humidity data. Products such as the GAS Enviro Controller and the Trolmaster Hydro-X enable you to adjust and set customised measurement intervals and monitor wide ranges of temperature and humidity levels. This is particularly useful as it gives you something for reference in the future which can highlight areas which you can improve. Alerts can be set when your set levels are exceeded to prevent deterioration of your plants.


13 amp GAS Enviro Controller


Trolmaster Hydro-X Complete Kit


Digital Series Thermometer/Hygrometer




Ventilation is another crucial element to take into consideration for successful plant growth. To remove excess heat, we recommend that you install extraction fans high inside your grow space.

Intake fans should be placed close to the ground, so cool air circulates through your plants’ leaves.

By having fresh air readily available to your plants, you’ll ensure a continuous supply of CO2, which is essential for the development of your plants. Depending on the conditions inside the grow space, you can set the fans to different speeds and maintain specific temperature levels.


VVIND Systems Wall Fan


Vortex 6" Clip on fan


Airbomz Co2 Can




In summary, we have learnt that you need to control temperature and humidity in relation to which stage of growth your plant is at. These factors will determine the photosynthetic rate of your plants, as well as other biochemical processes. To measure and control temperature and humidity levels in your grow space, you should opt for a thermometer and hygrometer, as well as a controller to increase/decrease airflow dependant on humidity changes.

With the right strategies and tools, you can create the perfect environmental conditions for your plants to grow healthy and strong. If conditions are optimised, you’ll achieve top-quality crops and heavy harvest yields.




Grow environment