Are you growing marijuana indoors?
Then you have a huge advantage.
Indoors, you control the environment completely. You can give your plants the perfect conditions to maximize growth and yield.
When it comes to humidity, the ideal level varies depending on the stage of growth:
- Seedlings: 70%
- Vegging: 50% – 60%
- Bloom: 40% – 50%
Of course, cannabis will grow just fine if the humidity inside your grow tent is outside these ideal ranges. But yields will suffer a bit if it is low. And if the humidity is very low, they will suffer a lot.
Since you have control over the environment inside your grow tent, why not provide the best possible conditions. Naturally, that means there may come a time when you need to increase the humidity in your grow tent. Here’s how to do that.
- 1 How To Increase Humidity In A Grow Tent
- 2 Raising Grow Tent Humidity: Final Thoughts
How To Increase Humidity In A Grow Tent
Before we get into the best ways to increase the relative humidity in a grow tent, we want to point out that you might not want to increase it at all.
Weed plants need the highest humidity levels when they are seedlings. That means there is a good chance that the reason you are looking to increase humidity levels is because you have seedlings that need a lot of moisture in the air.
Raising Humidity For Marijuana Seedlings
If your plants are seedlings, we recommend you don’t even bother trying to increase the humidity. 70% is a difficult level to obtain, especially in a large grow tent. Plus it can potentially cause issues with some equipment that might be in the grow tent.
Instead, it is much easier to create a smaller contained environment around the seedlings and to increase the humidity only inside this smaller environment, while leaving it untouched in the rest of the grow space.
The easiest way to achieve this is to put some kind of covering over the seedlings. We recommend a propagator tray with a humidity dome, but you can also just rig something up yourself.
The key is that you create a micro habitat around your seedlings in which it is much easier to raise the humidity than in the entire grow tent. You can simply use a spray bottle to mist the inside of the dome regularly, and that will suffice to keep humidity up.
If your plants are in the vegetative or the flowering stages of growth, creating a micro habitat will no longer work. If they aren’t too large yet, they soon will be. You’re going to need to raise the humidity inside the entire grow tent.
Increasing Grow Tent Humidity: Best Methods
There are a number of ways to increase the humidity inside your grow tent. We’ll give you all of the best methods below, so that you can decide which one will work best for you.
Use A Humidifier
If you need to consistently raise the humidity in your grow tent or grow room, nothing works better than a humidifier. It is the easiest solution and you can get pretty good ones for not much money.
There are a few things you want to look for in a humidifier. It should have a built-in humidistat. That way you can set it to automatically shut off once the humidity reaches a certain level and to automatically turn on when it drops below that level. It just makes your life much easier.
You also want one with a decent tank capacity, so that you don’t have to constantly fill it up. A 1 gallon tank should be the minimum in a small grow tent, and a 6 gallon tank in a larger tent.
If you can’t find a good humidifier that meets all the requirements, we have an article reviewing the best grow tent humidifiers.
For a larger grow room, try an evaporative cooler like this one, though these don’t usually have a humidistat.
If using the type of humidifier that sprays mist into the air, you want to make sure to use purified water, not tap water (this is actually a good idea with any humidifier to be honest). If you use tap water, it will result in mineral deposits on the leaves of your plants and the walls and floor of your tent.
An easier solution is to simply add water to your grow tent. You can do this by putting some bowls, buckets, or other container of water on the floor. Or you can hang a wet towel (or several) inside the tent.
Obviously, this method is not as accurate as using a humidifier, in terms of achieving the exact humidity and staying there. You will have to monitor and adjust until you get it where you need it. You’ll also need to refill any containers or rewet any towels.
Less ventilation increases humidity in two ways. First, air flowing around inside the tent dries up moisture. Second, air vented out of the tent by the extraction fan takes moisture with it.
Obviously, there are cases where it is not possible to decrease the amount of air you vent out of the tent. Maybe you are dealing with heat issues, for example. You always want to make sure you have sufficient fan power for your grow tent size.
But if you can reduce the strength of your extraction fan without causing other issues, this is an easy way to increase the relative humidity inside the grow tent. The best grow tent fans all have multiple speeds.
Reducing the temperature in your grow tent also increases the relative humidity, because colder air does not require as high a moisture content to become saturated as warmer air does. Obviously, you don’t want to resort to lowering the temperature, if it means lowering it below the ideal range for your plants and the current growth stage.
For cannabis, that means you don’t want to go below these temperatures for each stage of growth:
- Seedlings: 73° F (23° C)
- Vegging: 70° F (20°C)
- Flowering: 65° F (18° C)
Effects Of Low Humidity On Cannabis Plants
Plants do not only absorb water through their roots. They also get water by extracting moisture from the air through their leaves. If there is no moisture in the air, plants are not able to get water in this way and have to rely only on their roots.
That can be a problem, especially for young plants.
Clones do not yet have a developed root system, so they need to get most of their water from the air. That is why clones need an especially high relative humidity.
If the humidity is too low, clones might not root successfully at all. Even if they do manage to root, their growth will be stunted, because they still won’t be getting sufficient water.
Once plants are in vegging, they get more water from their roots, but they still rely on their leaves as well. Insufficient humidity during vegging can also stunt growth. It can cause nutrient burn, too, which can lead to yellowing leaves and eventually kill your plants entirely.
This happens, because insufficient moisture in the air means the plants have to compensate by taking up more moisture through the roots. In doing so, they also take up more nutrients, which causes an excess.
You can see why it is important to ensure your weed plants enjoy the correct humidity levels. If the air is too dry, it can lead to serious problems.
But make sure you don’t go too far in increasing humidity levels. Too much humidity can be even more harmful, especially during the flowering stage of growth.
Effects Of High Humidity On Marijuana Plants
The biggest problem associated with high humidity is bud mold or rot. Learn what mold on weed looks like here. Obviously, this only occurs during flowering, when buds grow.
Bud rot is the primary reason you want to keep humidity low during flowering. In addition to low humidity, you need good ventilation to ensure the buds do not accumulate moisture. Using the right size smart pots helps avoid this issue.
Another potential problem is a fungal disease called White Powdery Mildew. This can grow on plants of any age, which means they are especially susceptible in the earlier growth stages, when humidity is higher.
To combat this, ensure good airflow in your grow tent. An oscillating fan is great for this. The airflow keeps moisture from accumulating on the plants, even if humidity levels are high.
Raising Grow Tent Humidity: Final Thoughts
Low humidity, especially in the early stages of growth, can really stunt your plants’ growth. But be careful. High humidity can do much worse.
If your humidity is far too low, get yourself a humidifier and raise it, but if it is close, you might be better off doing nothing. Being a little low won’t affect much, but being high will. As is usually the case, keeping things simple is best. Learn how to keep it simple when growing weed indoors.