Keeping and growing plants is part art and part science.
That is equally true for cannabis cultivation.
You get a better feel for the ‘art’ portion of the equation as you get more grows under your belt.
The same is true for the ‘science’ portion. But unlike the art, you can research the science and actually get it right from the start.
When it comes to the science of growing cannabis, two of the most important factors are heat and humidity. You know the ideal levels of both (if not, we do cover that briefly below).
It is up to you to maintain those levels. Few factors have a larger impact on your grow being a success than getting the temperature and humidity right.
Today we will tackle one aspect of this: what to do if your humidity is too high. So let’s dive right in and learn how you can lower the humidity in your grow tent.
- 1 How To Lower Humidity In A Grow Tent
- 1.1 Different Growth Stages Need Different Humidity
- 1.2 Why Lower Humidity In Your Grow Tent?
- 1.3 Lowering Humidity In A Grow Tent
- 2 Lower Grow Tent Humidity: Final Thoughts
How To Lower Humidity In A Grow Tent
Cannabis is not a picky plant. It can grow in a variety of conditions. But if you give it the perfect conditions, it will reward you with much larger and much higher quality harvests.
And even the perfect conditions are not something the plant is picky about. It likes room temperature and average humidity. So nothing unusual.
That said, the ideal temperature and humidity levels do change as the plant grows more mature. The end result is that marijuana plants need far less moisture toward the end of their growth cycle.
Different Growth Stages Need Different Humidity
In the early stages of growth, the humidity level needs to be higher. Plants love high humidity in this stage. But as plants enter the later growth stages, the humidity level needs to be lower.
Here are the ideal humidity levels for each stage of plant growth.
- Seedlings and early veg: 70 – 75%
- Veg: 50 – 70%
- Flower: 40 – 50%
Generally, you won’t have any need to reduce humidity during vegging. In fact, depending on the local climate, you may have to take steps to raise grow tent humidity.
But during flowering, this changes. You might struggle a bit to keep humidity levels down. Unless you keep reading. Then you’ll know exactly what to do. But first, let’s briefly cover why you need to keep humidity in check.
Why Lower Humidity In Your Grow Tent?
Humidity in your grow tent can cause mold, fungi, rotten buds and mildew. It even slows down the growth of your plants.
The most common is something called bud rot, which is akin to the grim reaper for plants showing up in your grow tent. It manifests as a white powdery substance at first, then it gets gray, and finally black.
If your buds get bud rot or powdery mildew, they are useless and must be tossed out. Do not consume those buds.
What does bud rot have to do with lowering grow tent humidity? It is a direct result of too much moisture in the air, and the primary reason you need to keep humidity in check.
But bud rot and other types of mold and mildew are not the only reason. There is also an internal reason why you want to keep the moisture content of the air from getting too high.
Internal Health Effects Of High Humidity
External effects like bud rot and the mold and fungi that too much moisture causes aren’t the only potential problems. There is an internal complication that can spring up too.
If the air is saturated with moisture, your plants will not drink as much water from their roots. When your plants do not drink enough from the roots, they will not get the nutrients they need. Nutrient deficiency results in less potent and less healthy buds.
Basically, you really need to keep humidity levels where your plants want them to be.
Lowering Humidity In A Grow Tent
The good news is that it’s not that difficult to reduce humidity levels. But chances are you will have to spend some money.
You will almost certainly need at least a ventilation system, and maybe even an A/C unit or a dehumidifier. You need ventilation and possibly A/C anyway to regulate temperatures, so it’s not actually an additional expense. And dehumidifiers are not expensive.
Get A Dehumidifier
Wouldn’t it be wonderful if science came up with a machine that was designed specifically to remove moisture from the air, where all you would have to do is plug it in and walk away?
Well such an amazing machine does exist, and it is available at your local home improvement or drug store. You can also buy one online like this one (good for a small to medium-sized tent).
A dehumidifier is the simplest way to tackle the humidity problem, but they can be expensive if you have a large tent or bigger room. If you decide to go this route, just make sure to do your research and match the size of your area to the right kind of unit.
Commercial Grade Dehumidifiers
If you have a large operation or if you are doing this for money, you should seriously consider jumping straight into a commercial grade dehumidifier.
The small ones made for normal use are great for little tents or hobby growers, but they give you no control over the humidity. They are either on or off, with no in-between. While this is fine for most people, it is not adequate if there is significant money at stake.
A commercial grade dehumidifier can constantly monitor the relative humidity in the room and adjust when it needs to remove moisture vs when to rest and let the water vapor collect. This is a great model, if you are considering picking one up.
If you are not concerned with the ability to ‘set it and forget it’ or if you have a small operation, you have no need for a commercial dehumidifier. You will be fine with a small, everyday-use model.
Ventilate Your Grow Tent
Bring new air into the tent from the outside can help lower the humidity, assuming you do not live in an extremely high humidity area. Of course, if you are going to bring in new air from outside, this means you will also be exhausting air from the tent.
For small tents, you actually only need to blow air out of the tent. The resulting negative pressure will automatically suck new air in. To exhaust the air, you’ll want a good inline fan for your grow tent.
With larger tents, or to avoid tent suck, you need a second inline fan to blow fresh air back into the tent, to replace the air you are sucking out.
Humid air is heavier than dry air, so if humidity is a huge issue and temperature is not a big problem, you might consider setting up an exhaust fan down low. Generally, it is better to put them at the top of the tent, though, since that is where hot air gathers.
You can also increase circulation among the plants by keeping more space between them. You can move them further apart and you can trim off the lower branches of each plant.
This creates more space for air to flow and the lower branches don’t produce buds anyway. You get a better harvest without them. Make sure you use only the best weed trimming scissors. Bad ones will not cut cleanly.
Do Not Water More Than Necessary
Overwatering your plants always leads to problems. Too much water (especially with poor drainage) can cause nutrient issues and root rot, which makes your plants anemic and sickly. Excess water also makes the air too humid.
Make sure you are following the science when it comes to watering your plants. Too much can make your plants miserable. And thus, you as well.
How Much Water Is Too Much?
This is a subject that requires its own book (and there are many out there already!). But it is relevant to lowering the humidity in your tent, so we will cover the very basics here.
Depending on your growing medium (soil or other types) and drainage, this can vary wildly. In general, you want to water your plants until the soil is nice and drenched, and then let the soil dry out before doing it again.
If you have average soil and proper drainage and semi average size growing containers, this equates to roughly one good watering every 2-3 days. The key here is to not saturate your soil when it is already wet!
There is a rule of thumb that can serve you well Water less; water well. The idea is to completely saturate your plants infrequently, instead of a little watering all the time.
The latter leads to roots that are always wet, which creates an environment ripe for root rot and other issues that can harm your plant. Plus it most definitely makes the air too humid.
Lower Grow Room Temperatures
Relative humidity and temperature go hand in hand. If temperatures are higher than ideal, that is fine as long as the humidity is lower. And vice versa.
This means that you can, in essence, offset a higher than ideal humidity by keeping the temperatures lower than ideal.
That said, this is really only a good idea if you just can’t seem to get those humidity levels down. It is much better to actually lower the humidity and keep the temperature where it should be. But if your temps are too high and that is the reason for your humidity problems, definitely cool your grow tent!
Consider An Air Conditioner
An A/C unit is the easiest way to bring down temperatures. As mentioned, not only is this an important part of the health of your plants, it is also an easy way to quickly bring down the relative humidity in the air.
There are units that stand alone or are on rollers, so you do not need to mounted them on the wall. This is perfect for tents. They have an exhaust tube that you need to lead out through an opening in the tent.
Cooling the air and moving it around will decrease the air’s capacity for holding water. The colder the air the less ‘space’ there is for water to live.
Lower Grow Tent Humidity: Final Thoughts
Higher humidity levels are great during vegging, but during flowering, especially the latter stages of flowering, you need to drastically reduce the moisture in the air. Failing to do so will result in a poorer (and perhaps completely ruined) harvest.
There are a number of ways to lower the humidity in your grow tent, but the most efficient are sufficient ventilation and proper airflow. Keeping temperatures in check is important as well.