Grow Tents temperature and humidity: the base to grow successfully

February 11, 2025

Scritto da: Gsi Team

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Categoria: Environmental measurement tools

Maintaining the right temperature and humidity parameters into your grow tents is a fundamental factor in ensuring success in indoor cultivation. The ideal range for cultivation temperature and humidity strictly depends on the plant grown and the growth phase they are going through (germination, vegetative, flowering, fruiting). Temperature and humidity for weed are parameters closely linked to each other, excessive heat within the cultivation environment leads to a sudden evaporation of the water present in the soil and in the air around the plants with a rapid lowering of the humidity rate.

If humidity is not restocked, after a while the growing environment will be dry, and the heat will begin to evaporate the water present inside the plants, seriously compromising their health. In the hours of darkness the temperature drops and the humidity rises. It must be said that a correct symbiosis between humidity and temperature is also greatly influenced by an adequate ventilation system, a correct setting of the air exchange will help to keep our parameters. Generally, as regards the Grow Room Temps, it is mainly influenced by the Lighting System which, depending on the type of system used, can generate different levels of heat.

The temperature can be kept under control by an adequate ventilation system, just as a cold humidifier can lower the temperature by a few degrees. The climate outside the Grow Room can also influence the temperature inside, raising or lowering it depending on the season in which we grow.
The humidity in the Grow Room is generated mainly by the irrigation that is carried out, by the mass of the plants and therefore by the number of plants present in the room and by the systems that generate humidity such as the Humidifier, a system that generates it artificially in case our cultivation requires a boost for this parameter. The humidity rate, as we mentioned previously, is influenced by the temperature and how it can also be kept under control by a correct setup of the ventilation system.

The ideal cannabis growing temperature for your grow tent

The first step when we are going to setup a new grow tent is to try to recreate a healthy climate for our plants. Ideal temperature and humidity are the main factors that influence the plant's growth. Only with adequate Climate Control you will reach a correct balance of these parameters, an essential practice that must always be implemented and can be kept under control using specific tools such as a Digital Thermo-Hygrometer. These two factors are the basis that will determine a successful harvest, affecting both the growth and final quality of our plants.

The temperature is measured in degrees Celsius (°C) while the humidity is measured as a percentage (%) of the water vapor present in the air molecules. When the humidity rises above 90% the air in our cultivation place becomes saturated with water which settles on surfaces such as (leaves, vases, walls) not allowing correct transpiration from the stomata (pores) of the leaves, increasing furthermore the risk of molds such as botrytis. Otherwise, when the humidity drops below 40%, the plant will begin to close the stomata; not allowing correct transpiration and significantly slowing down its growth speed.

Environmental humidity is called "relative humidity (R/U%)" because the air's ability to trap water vapor is not an absolute value, but relative to the temperature of the air itself. So warmer air will hold more moisture, while cold air will hold less. The moment we pass from day to night is an excellent example of how relative humidity levels can go out of control, as happens in indoor growing after a few minutes after turning off the lighting system its temperature progressively decreases in the grow box and within a few moments the humidity will rise dramatically, since usually together with the Indoor Lighting the Air Extractor also turns off.

This sudden change will cause an immediate increase in humidity to dangerous thresholds. In this regard, it is good practice to leave the air extraction turned on during the dark period, better at minimum if the extractor is dimmable, otherwise by adjusting it with a potentiometer or a digital timer, interspersing a few on and off cycles during the hours of darkness. An excessive increase in humidity during the flowering period will facilitate the emergence of pathogens such as mold and fungi.

Useful tools for climate control, the importance of the humidifier in grow boxes or grow rooms

Having both an air extractor with power related to the cubic meters available and an instrument that monitors and records temperature and humidity (thermohygrometer) inside your room or cultivation place is of fundamental importance. To modify or intervene on these parameters there are obviously a series of tools suitable for every situation and need. They are useful tools for intervening and regulating parameters in cultivation environments.
In this regard, another basic tool in grow tents is the humidifier, with this tool you can easily change the values in even large grow rooms.

Control units for temperatures and humidity. They are control units to which it is possible to connect the instruments for air extraction and introduction, which will be dimmed according to the desired percentages that will be set on the climate control control unit.
heaters and stoves. Electric heating appliances, such as bath heaters and small heaters.
greenhouses and heated mats. Mini greenhouses with heating mat useful for the seed germination phase.
humidifiers and dehumidifiers. Useful tools for increasing and decreasing relative humidity percentages.

Grow room temeprature and humidity tips

Like any other plant grown indoors, the Temperature and Humidity parameters for Cannabis must be constantly monitored, if they change we must be able to intervene preventively to avoid the onset of very serious problems, high temperatures and lack of humidity and vice versa, they can lead to pathologies such as mould, sunburn, slowed growth, earing, parasite infestation, etc.
In grow tent cultivation generally and in our experience, whatever the problem: imbalances, deficiencies, excesses, etc... if you intervene quickly and with knowledge of the facts, it is possible to re-establish easily the ideal conditions of health and vigorous growth of each plant.

Specifically mentioned above, when humidity is scarce, the umbrella-like attitude of the plants can be recognized in an attempt to conserve humidity, up to the phenomenon of necrosis of the leaves. With high temperatures, however, spike phenomena will occur with increasingly longer internodes and very small leaves that tend to curl.
Temperature is equally important for the success of indoor cultivation. It is also a basic factor that strongly affects speed and final production. The plants love a temperate climate usually between 14 and 29 °C as occurs in the months between spring and summer. As happens with humidity, above and below these values the plant begins to defend itself, significantly slowing down or even blocking its growth.

In indoor growing, usually, especially in the warmer months, it is not uncommon to have high temperature problems for growers who use MH or HPS lamps which notoriously emit great heat. When this happens, if you do not want to interrupt cultivation in the summer months or buy an air conditioner which would burden electricity costs, it will be necessary to obtain special Cooltube, Cool Junior or Xtracool reflectors, which can be connected directly to the ventilation system, which favor the expulsion of the 'warm air from the grow tent. The opposite problem should not be overlooked either, i.e. the low temperature in the environment in which it is grown, which would cause growth to stop, whereas discharge lamps are a healthy touch.

The entire life cycle of Cannabis consists of three main phases: germination, vegetative and flowering. Each phase requires certain temperature and humidity parameters which, for correct development and success of the harvest, must be followed scrupulously. Being able to keep the grow tent temperature and humidity under control is a first and fundamental step in obtaining healthy and lush plants, drastically reducing the possibility of problems arising during the entire cycle that would significantly compromise our long-awaited harvest.
Let's now look more closely at the right temperature and humidity parameters to respect in each phase

Choosing the perfect growth and flowering weed temperature and humidity parameters

By indoor vegetative phase of Cannabis, we mean the first part of the plant's life, in which the entire plant system is physically developed, from seed germination to the pre-flowering stage, including the root system. The plant structure is fundamental and will then support the entire flowering phase. The best humidity and temperature parameters for growing weed to follow for good indoor growth are:

Humidity Germination Phase : 80% . Maintaining a high humidity level during the germination phase is essential for the seed to hatch. If it is not possible to maintain high humidity the seed will not germinate, it is advisable to equip yourself with Mini Greenhouses suitable for germinating seeds.
Germination Phase Temperature : 18°C / 24°C . During the germination phase, dropping below 18°C means interrupting the seed hatching process. For this delicate phase of the plant, if you have problems maintaining the weed growing temperature, we recommend purchasing Heated Mini Greenhouses.
Vegetative phase humidity : 60% / 70% . Maintaining a high humidity level during the growing period will ensure that your plants grow quickly and healthily. If it is not possible to maintain high humidity it is necessary to purchase an Ultrasonic Humidifier which produces cold humidity.
Vegetative Phase Temperature : 14°C / 29°C During the growth phase, going below 14° or exceeding 29° will literally block the development of the plant. Both in the case of too much cold or too much heat, the plant practically enters a state of hibernation, slowing down all the vital processes for plant development.

The Flowering Phase of Cannabis includes that period of life that goes from pre-flowering to the last stage of floral maturation, which corresponds to the moment in which the white hairs turn brown and wither. This is also the moment in which there is the maximum concentration of THC, of greatest interest for production for commercial or recreational/therapeutic purposes, from this phase onwards the organoleptic qualities of the flower decay and if the bud has been pollinated they will begin to ripen the seeds inside the calyxes. The indicative humidity and temperature parameters to follow for good flowering are:

Flowering Phase Humidity : 50% / 60% . During the flowering phase, a decrease in relative humidity will be necessary to avoid the risk of mold appearing. So we will always keep the extractor on even during the dark hours.
Flowering Phase Temperature : 14°C / 27°C . During the flowering phase it is recommended not to exceed 27°/28°. The high temperature can compromise the development of the flower, leaving it airy "not compact" and decreasing the formation of the resin and degrading its active ingredient.