Understanding Humidity and Temperature for Cannabis

When we are hot, we sweat, which causes us to drink water to replenish ourselves. By maintaining grow room temperature control, we can encourage our plants to transpire (the equivalent of sweating). When our plants are sweating from the underside of the leaves, the plant reacts by taking up more water from the root zone

The root zone is where we add our plant nutrients, and when the plant is taking up water from the root zone, it is also taking in nutrients. By understanding indoor climate control, we can increase our plants' health and yields through increased nutrient uptake. 

You might be thinking, if I make my grow room conditions really hot, my plant will sweat a ton and uptake mega doses of nutrients and be super big…. but that's not a good idea.

Optimal Temperature Range for Cannabis Plants in Grow Tents

seedling stage

First off, the seedling stage will benefit from warm temperatures. The additional humidity in the air is beneficial to the growth above the surface, but the warmer temperatures also encourage seed germination and root growth. If the temperature is too cool during this stage, growth can slow, pathogen pressure can increase, and that can lead to damping off (seedling death). The ideal temperature range for a cannabis seedling is 21-28 °C (70-83 °F).

vegetative stage

Driving growth in the vegetative stage is directly related to the number of flowers you will harvest later. Grow room temperatures are similar to those of the seedling phase. The goal of using this temperature range is to increase transpiration (plant sweating) and drive nutrient uptake from the root zone. This will help the plant grow sturdy branches and plenty of bud sites. The ideal temperature range for cannabis in the vegetative stage is 21-28 °C (70-83 °F).

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Tips for Controlling Humidity in a Grow Tent

Part of controlling your humidity is controlling your temperature. Tools like an exhaust fan and the internal circulating fan(s) not only help control temperature but they assist in the fight against high humidity too. Dehumidifiers can be used to lower the humidity of the grow tent or lung room. Just the same, humidifiers can be used to increase humidity if needed.

Some of the less obvious culprits of high humidity include:

• soil mass
• time of day you water
• plant density
• amount of foliage

The more soil you have in a grow tent, the larger the amount of moisture that will be released into the atmosphere through evaporation. I like the idea of growing in beds instead of pots, but even a 3x3 bed of soil in a 4x4 grow tent creates an almost unconquerable battle with humidity because of the large soil mass and all of the moisture it is capable of retaining. So, if you have a small tent, I recommend you stick to growing cannabis in pots!

Additional Tips for Cannabis Climate Control in Grow Tents

Most tent growers are growing inside a house or apartment, which provides a unique opportunity for controlling grow room conditions. Using the existing heating and cooling systems of the house, the lung room (the room your tent sits in) can be kept within the ideal ranges, conditioning the air inside of the grow tents. 

1. If you’ve placed your grow in a garage, basement, or attic, adding insulation foam boards around your grow tent can offer a level of climate stabilization that will aid in your grow tent climate control efforts. If you are on a concrete floor, be sure to raise your pots off the ground to avoid a cold root zone, especially in winter.
2. A popular trick amongst experienced growers is to run your lights at night when it is cooler outside and turn them off during the day when it is warmest outside. If you struggle with heat in the grow tent, is your grow tent located against an outer wall of the house that gets direct sunlight (heat)?
3. If you need to add moisture and cooling to your environment but you are on a budget, Swamp Coolers are an easy and cheap solution that you can make at home, courtesy of evaporative cooling.

Troubleshooting Tips for Temperature and Humidity Cannabis Climate Control

A new grower might assume that the smaller the grow tent, the easier it will be to control temperature and humidity. The opposite is actually true. Smaller spaces take less time to heat up from the equipment and less space for plant transpiration to go. So, first, consider the size of your grow tent. I find that the climate is easiest to control in grow tents 4x4 or larger.

“Aside from these, you may need a humidifier, dehumidifier, space heater, or even a small A/C unit depending on the climate where you live.”