How to raise or lower humidity levels in your grow tent.
Having issues with humidity in your grow tent? This is a pretty common problem among indoor growers, and there can be some pretty serious consequences for both you and your plants if it is not dealt with. The most common way of dealing with this issue is to install a proper ventilation system with oscillating fans inside the tent to promote airflow. Though before you buy an inline fan and vent system, there you should first educate yourself on why you need it and what equipment to buy so your household does not become plagued with mold and mildew.
What is causing the humidity?
The humidity in your grow tents will rise and fall based on a variety of factors. The reason there is humidity in a tent is mainly the result of a process called ‘transpiration.’ This is the process of water moving through the plant and being naturally expelled as water vapor from the stems, leaves and flowers of the plant.
One of the biggest factors for humidity is how many plants you have growing in your tent. The more the air in your grow tent becomes replaced by plants, the more they act as natural windbreakers, preventing air from fully circulating the tent and cycling in fresh air. The less air movement there is, the more water vapor is trapped in the tent, directly affecting humidity levels.
Why is the humidity level such a big deal?
The humidity level in your grow tent is important for a variety of reasons. Firstly, the high level of humidity can hinder the growth of your plants as it can affect the transpiration rate of your plants, forcing plant metabolic rates to decrease.
Secondly, high levels of humidity and heat in your grow tent is a welcome invitation for mold and mildew that can pose health problems for both yourself and your plants. Plant leaves that are sitting on top of each other collect moisture between them and generate mold and mildew. As well, if the tent is not regularly cleaned mold and mildew can grow almost anywhere, affecting air quality for your plants and your home.
It is important to keep humidity in check for these reasons. Make sure to invest in a hygrometer and place it in your grow tent to keep an eye on this important data. There are basic digital thermometers that have built in hygrometers, so you can invest in one of these and kill two birds with the same stone.
How do you deal with humidity issues in your grow tent?
The typical solution for dealing with humidity levels in your grow tent is to install an inline fan. To help circulate some of the humid dead air inside the tent it is also a good idea to ensure you have some oscillating fans inside the tent as well. Though be sure when you are purchasing a fan to consider a few factors. These include how loud it is, fan speed and airflow, and safety certifications.
Grow tent vents typically have ties that will wrap around a smaller ducting tube, so it is important to get an inline fan that is the same size or smaller than your vent diameter. Typically an inline fan that is 4” in diameter will provide the ventilation that is needed up to a 4x4’ grow tent, depending on how big and hearty the plants are, and how many plants there are in the tent. To invest in a fan larger than this is unnecessary and could actually make more problems for your grow space.
The larger the fan, the more powerful it is. This means more air will be be flowing through your tent, which sounds like a good thing- but too much airflow and humidity levels may not be high enough. Also, the passive air inlets of your tent may not be enough of an opening to fill the void produced by the inline fan, meaning it will be forced to pull air from other air inlets in your tent that do not have a mesh filter preventing dust and other particles from entering the space, such as zipper holes, cable ports and more. Possibly the worst case scenario from this situation is that an inline fan that is too powerful for the size tent you have will create ‘negative air’ in the tent, meaning that air is being pumped out faster than it is coming in, creating a vacuum where the plants are basically being suffocated from lack of air and oxygen. A simple fix for this is to purchase a smaller inline fan and ensure it either comes with, or has a speed controller built in. This will allow you to turn down fan speeds and control airflow and humidity levels with much greater ease.
Ensuring your household does not have to deal with mold and mildew is as easy as keeping a clean grow space and installing a carbon filter and inline fan to keep humidity levels in check.
Another solution for controlling humidity in your grow tent is by using a humidifier/dehumidifier. For the smaller grower I would not recommend this, typically humidity issues can be solved with proper airflow and ventilation management. Although if you plan to grow in a larger space with many plants, this could be a good option for you. The larger the space, the harder it gets to control temperature and humidity, so it is helpful to manage these factors with automated mechanics such as a dehumidifier that will auto adjust humidity levels with the touch of a button.
Now you are ready to purchase an inline fan and carbon filter kit. Make sure it is properly installed to avoid the issues discussed in the previous paragraphs, and visit my product recommendations page for brand comparisons in terms of value, price and features. Good luck, and happy growing!
A common question I get asked is when you are growing in a grow tent, where should you put the thermometer to get an accurate reading?
It is a valid question to ask, because depending on the size of the tent and the type of lighting you are using readings could vary drastically from the top to the bottom of the tent. Things get even more complicated if you are using a thermo hygrometer and want accurate readings of humidity levels as well. You are right to do your research and make sure you are getting accurate readings, as temperature and humidity levels can often be the cause of a list of problems for your plants. This article will address the question of where to place your thermometer, and educate you on typical symptoms your plants exhibit when there is trouble brewing with temperature or humidity levels.
There are a few solutions to the question of where to put your thermometer in your grow tent. The quick and simple answer? Everywhere. But how can temperature vary so much in such a small space? It really does depend on what you are growing, how much of it you’re growing per square meter, the type of lighting you’re using and the quality of ventilation and airflow you have. All of these factors play a part in your grow environment, and all of them can change temperature levels significantly. Let me explain.
For instance, if you are using an HID light in your grow tent, this type of lighting emits a large amount of heat. Left unattended this heat would sit at the top of the tent, and slowly creep down to your plants the longer it says on. Installing a proper inline fan and ventilation system helps to dispel this stale hot air, but it does not mean heat is not being generated and emitted regularly by the light. Placing a thermometer too close to this light will throw off temperature readings as it would likely be much hotter an inch from the light than it would be at the bottom of the tent. Alternatively, placing your thermometer at the bottom of the tent will not necessarily give an accurate reading of temperature near the plant canopy.
So how to solve this conundrum? Solution 1 is to simply purchase 2-3 cheap thermometers or thermo hygrometers and place them at height specific intervals throughout the tent to get an idea of temperature and humidity at the plants roots, base, and canopy. Another more temporary solution is to rotate where you place the thermometer in the tent on a daily or bi-daily basis. This should give you a fairly accurate reading so long as external factors around the tent are not affecting readings too much. This means that outside or household humidity and temperature levels are not fluctuating by too much when moving the thermometer to the next location.
If you choose to rotate your thermometers location, or even if you took the safe route and purchased several thermometers, be sure to keep a look out for temperature and humidity related symptoms with your plants. When growing cannabis a typical sign of under temperate conditions is when plant leaves begin to darken significantly and even turn purple in colour. Conditions that are too cold and you will be lucky if the plant survives the night. If it is too hot on the other hand, and your plants leaves will begin to fold in half.
While an environment that is too hot will not directly lead to plant death, it does weaken the plant and delay growth, which opens the door to other problems such as pests, mold or the leaves being burnt. Other symptoms that are a bit more general, but could be related to temperature include leaf edges looking burnt or turning brown, curling leaf edges, wilting or drooping leaves, or the entire plant looks to be wilting or drooping.
So it’s therefore important to regularly check the temperature and humidity of your grow space. Having a few strategically placed thermo hygrometers will help to identify any issues with your grow environment and help you address them before they become an issue for your plant. Now you’re ready to take on your grow environment with this added knowledge. Get what equipment you need, and start growing! Check out my equipment recommendations page, or click here to see what the best value equipment on the market is and where to find it.
'Prof' is a professionally trained Canadian teacher with a love of horticulture and advocate of the democratization of cannabis cultivation, especially for medicinal purposes.