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How to Lower Humidity in Your Grow Tent

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Lower Humidity in Grow Tent

Cannabis plants can be a bit temperamental. Different strains need different levels of humidity to thrive. But that’s not all. They even need changing levels of humidity during their various stages of growth. But knowing the proper humidity levels to keep your grow tent at is only part of the battle. You must then get the grow tent to maintain the proper level of humidity to keep your plants growing at their full potential. Often, while trying to increase the humidity level of your tent to satisfy your plants, the moisture in the air can get to be too much and you’ll need a way to decrease it so that your plants don’t experience adverse effects. But how exactly do you go about lowering the humidity in your grow tent? In this article, we’re going to discuss how you can decrease the humidity level for your plants, as well as going over the detrimental effects that too much humidity can create.

Measuring Humidity in Your Grow Tent

Before we can properly adjust the humidity levels in our grow tents, we need to know exactly what the current level of humidity is. To measure the humidity in your grow tent, you’re going to need a tool called a hygrometer. This device simply measures the humidity in the environment and gives you a reading in percentage form.

The older style hygrometers used a dial with a rotating needle to indicate the humidity level. Newer hygrometers are generally digital. They display the humidity percentage as a digital readout. Most of them also include a thermometer so you can gauge the proper temperature at the same time. You can simply leave this little device in your grow tent all the time so that you can effectively monitor the humidity level and adjust accordingly.

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Optimal Humidity for Cannabis Plants

 Cannabis plants go through several life stages during their maturation process. From seedling to flowering, their humidity needs start high and taper down as the plant grows. Matching the proper humidity level to each stage of growth is very important to avoid the detrimental effects of too much or too little humidity. The following recommendations are generalized, so keep in mind that each strain has specific preferences that you’ll need to try to match.

The youngest plants, seedlings and clones, need the highest levels of humidity. At this stage, humidity levels of 65%-80% are ideal. To achieve this, it’s recommended that you keep your babies in a propagator that will keep them warm and moist.

Once your plants enter the vegetative stage, they’re going to need a lower humidity level. At this point, they’re going to react best to humidity levels between 55%-70%.

After vegetating, your plants are ready to begin flowering. Once they reach this phase, humidity levels will take another drop, falling to 40%-50%. As they start to get later into the flowering stage and near harvest time, you’ll want to decrease the humidity again. Now the humidity of your grow tent should be between 30%-40%, the driest time in your plants’ life cycle.

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Negative Effects of Too Much Humidity

Now we know approximately how much humidity our cannabis plants need to reach their full potential. But what if the humidity gets higher than it should? Let’s discuss some of the negative effects that can occur when humidity levels are too high.


It’s no secret that mold and mildew form in wet areas. You can see this in showers and bathrooms all over. But when it happens to your cannabis plants, it’s a very bad sign. Mildew and mold can be poisonous for humans, and smoking them on your harvested buds is not a good idea. Once mold and mildew form, you’ll have a very difficult time eradicating it, so it’s best to avoid this problem altogether.

Bud/Flower Rot

If conditions get too wet, your plants can actually start to rot. The unfortunate part about this problem is that you won’t notice it until you start to harvest. By this point, you’re far too late to do anything about it, so your entire grow will be a waste. It’s hard to imagine anything more disappointing than an entire cannabis crop lost to bud rot.

Decrease CO2 Intake and Growth Rate

When humidity is too high, your plants can’t intake enough CO2. This results in reduced photosynthesis, so your plants won’t be growing as efficiently. In some cases, growth can stop completely. Naturally, this is the last thing we want, so it’s important to keep humidity levels in check if you want to see your plants grow to their fullest sizes.

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How to Lower the Humidity in Your Grow Tent

So, what should you do if the humidity in your grow tent is too high? We know it can ruin the harvest, so it’s important to get the jump on this issue right away. As soon as your hygrometer tells you that it’s too moist in your grow environment, implement one or more of the following strategies to reduce the humidity and save your crop.

1. Increase Ventilation and Airflow

When you increase the amount of fresh air that’s circulating in your grow tent, you’re causing the air to recycle faster. This means that the humid air is being replaced by drier air, decreasing the overall humidity levels in the tent. You can start by just increasing the level of your current fans. But if that’s not enough, you can always add another fan or more ventilation to decrease the humidity further.

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2. Raise the Temperature

When you raise the temperature in your grow tent, the relative humidity decreases because the air can hold a higher volume of total water. This means you can add another light or reduce some of the cooling you’re using now. Raising the temperature just a few degrees could result in a humidity decrease of several percentage points.

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3. Add a Dehumidifier

Dehumidifiers pull the water from the air and hold it until you empty them. Adding a dehumidifier to your grow tent is one of the simplest and most effective ways to decrease the humidity in your grow environment. They’re also extremely easy to use. Just put it in your tent and turn it on. It will automatically turn off when the water tank is full. Then you can empty it, check your hygrometer, and run it again if conditions are still too humid.

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4. Avoid Over-Watering

It may seem like a no-brainer, but over-watering is actually one of the most common culprits of too much humidity in a grow tent. It’s very easy to over-water your cannabis plants. Make sure that the top inch of the growing medium is dry before you add more water to your plants. If you’re watering them every day, you’re probably over-watering them. Watering your plants every two to three days is usually the sweet spot.


Every cannabis cultivator desires to grow a green garden of beautiful and healthy plants that yield large, dense buds of high potency. To achieve this, you’re going to need to give your plants ideal conditions, which means keeping your grow tent at the proper levels of humidity. But too much humidity can have detrimental effects such as bud rot and mold. To avoid this, you’ll need several tools to help you combat the humidity when it reaches levels that are too high for your plants. The easiest way to fight this is to avoid it altogether by ensuring you never over-water your plants. But if humidity levels still climb higher than they should, you can try adding a dehumidifier, raising the temperature, and increasing ventilation and airflow.

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