10 Ways on Raising Humidity in Grow Tent [Budgetwise]

Watching your plants to dry out is the worst nightmare for any grower. If we put issues like stressed up plants, immature plant roots on top of that, that’s the doom’s day for you.

Guess what, all these issues have their roots into one particular cause- Low humidity in grow room.

Therefore, we’ve decided to craft an all-in-one guide on raising humidity in grow tent. We’ve broken down the grow humidity basics, ideal humidity levels in grow tent and 3 phases on how to increase grow tent humidity.

Grab a cup of coffee, buckle your seatbelt and let’s dive deep into the guide-

Grow Room Humidity: The Basic Knowhow

Before we begin, it’s time to recall some science.

Long story short- humidity is the amount of water vapor that air can hold. But that’s not how gardeners recognize it.

There are three ways to address humidity- absolute, specific and relative. And the most convenient one of them is Relative Humidity(RH). So, we’ll only stick to that anyway-

What Is Relative Humidity?

The relative humidity is a percentage, which shows up the ratio of current moisture content and the most possible moisture content of a certain amount of air.

The formula says-

R.H.= (Actual Vapour Density/Saturation Vapor Density) x 100%

The higher the grow room humidity percentage is, more vapors take place in the air, and the more humid your grow room feels. And vice versa.

That being said, there are very active effects of other environmental factors like-

  1. Temperature: RH goes up as temperature rises, and vice versa.
  2. Light: RH goes up as light becomes more intense(bright), and vice versa.
  3. Ventilation: RH goes up as air ventilation becomes less, and vice versa.
  4. Irrigation: RH goes up as irrigation(waterflow) increases and vice versa.  

Seems confusing? The next section is solely for you, then-

RH and Other Environmental Factors

Humidity and Temperature
Humidity is inversely related to the temperature of your grow space. While temperature increases, the air’s ability to hold vapor decreases. So, you’ll have a low RH underneath the lights, where the temperature is higher than cooler areas like the ceiling or vent openings.

Humidity and Light
Light does not have a direct impact on the humidity of a given space. But typical grow lights are quite heated generation, which impacts on the humidity of the room. If you don’t ensure a proper air-cooling system around the lights, this will eventually impact on the humidity.

That being said, using cooler lights like LEDs is a smarter option from every point of view.

Humidity and Ventilation
Ventilation impacts on the air inflow and outflow of the grow room. Thus too much ventilation will bring on quicker air circulation, which won’t let the grow room become humid enough.

On the other hand, slow ventilation will trap the air and the humidity and temperature beneath it.

Therefore, neither too much ventilation nor too slow ventilation is good for growing.

Humidity and Irrigation
Abundance of water resources provides more water surfaces to source the vapor form. More vapor in air means more % of RH.

As a matter of fact, there are a number of irrigation systems in a grow space like- manual watering, drip watering, flood watering and so on. If these surfaces are close to the intake tubes or vent holes, it’s more likely vaporize, and make the air more moist.  

Is Your Grow RH Perfect?

Measuring RH In Grow Room

AcuRite 01083 Thermo-hygrometer

The best way to measure your grow room humidity is to use a grow room humidity meter(hygrometer). There are many models available in the market, and most of them are electric thermo-hygrometer combos.

However, there are two kinds of electric thermo-hygrometer combos available. In case you’re interested, here is how they work-

Resistive Electric Hygrometer

Electricity passes through a ceramic substance which is in air. With increased humidity(water vapor), the ceramic contracts, and that changes its resistance. And the degree of change is converted into a change of humidity.

Capacitive Electric Hygrometer

It uses a capacitor(two plates with air in between) style setup. The humidity of the air between the metal plates defines how much charge these plates can hold. Thus, the degree of humidity comes out in numeric values.

What Are The Right Grow Room Humidity Levels?

In different stages of a plantation, their humidity requirement is different. A rule of thumb is, relative humidity should never exceed 70% at any condition.

However, we need more specific humidity requirement in grow tent. And here it is-

Table: Ideal grow room humidity for every grow stages

Growth StageRequired RH Why?
Seedlings/Cloning70-75%To keep plant roots stay stress-free and growing.
Early Vegetative Stage60-70%To let both roots and leaves to intake water and moisture.
Late Vegetative Stage55-60%To prepare the plant for flowering.
Early Flowering45-55%To let the plant stay in neither too cold nor too hot environment.
Late Flowering40%To prepare the plants for harvesting
Harvesting35-40%Not to create any molding issues.

Why Humidity Is A Big Deal for Grow Plants

Big question! But the answers are almost Here are the answers-

It Lets You Control Your Plant’s Nutrition

Grow plants need to keep intaking water through their leaves and roots. When the humidity is sufficient, they absorb moisture(water) through their leaves. This lets them drink less water through the roots.

On The other hand, lack of humidity in the air causes the plants to drag more water through roots. And as we gardeners put nutrients in the water, the more they drink it, the more nutrient they take.

Summary line? Learning how to control grow tent humidity is the synonym of having control over the nutrition of the plants.

It Affects on The Health & Growth

Plants love to live in a high humid environment when they are young. And over time, they get mature and asks for a less humid environment.

Therefore, the abundance of humidity is a key factor to ensure the proper growth of plants, specially when they’re tender.

In another way, if plants have to drink more water due to lack of humid air, this will put more stress on the roots. This stress will eventually lead into dehydration, stomata closing and the overall health of the plants.

3 Phases of Raising Humidity in Grow Tent

How you’ll battle low RH level, depends upon your efforts.

We think the best way to raise the humidity in grow tent is through a set of actions. These actions would be determined by your budget and intention to give efforts.

Therefore, we’ve laid out a 3-phase guide towards achieving high humidity. Now let’s get going-

Phase 1: No Cost Modification

In this phase, you can modify your existing grow tent equipment to raise humidity. But keep in mind that these methods won’t fill up your humidity gap fully.

Get Rid of Half the Fluorescent Lights

The science is simple here. You already know that humidity decreases with temperature increase. And guess what, fluorescent lights emit heat.

In short, fluorescent lights decrease humidity.

So, removing half of the fluorescent lights is an easy way to raise the humidity in grow room.

Lower your Fan Speed

Ventilation is always a crucial part of growing. Without proper ventilation, your grow tent won’t see an exchange of air.

People normally set the fan speed at moderate. This helps in conserving moisture at different stages of plant growth.

If you set your fans at high speed, then two things will happen-

  • The air will dry up faster than an average rate resulting in very low humidity in grow tent.
  • Vapor won’t be able to sit on the leaves resulting in low moisturization of the plants.

So, it’s quite possible that high fan speed could leave your plants in dehydration.

Now, what to do with the fan speeds if I wanted to increase the grow tent RH?

In short, set the fan speeds at the lowest possible level.

The low fan speed will circulate less grow tent air. This will increase the humidity in grow tent air.

As a result, humid air will be in touch with grow plants constantly. Remember that this method alone won’t take your grow tent RH jumping to 70%.

Modify AC Settings to Drop Temperature

As we have discussed earlier, the temperature drop helps in building humidity.

If your air conditioner fails to cool down the grow tent, then it’ll be impossible to increase the RH level.

So, check out if your air conditioner can cool down even more. See what its thermostat range is. Check out if, at the lower range, your AC cools off the grow tent perfectly.

Phase 2: Low-Cost DIY Humidity Hacks

It’s okay if the previous zero budget methods weren’t enough for you.

If you’re ready to spend a bit of money for humidification, but with a light wallet, then this is the right spot for you.

We’ve gathered up some low budget hacks that might just do the trick for your grow tent without using a humidifier.

So, let’s explore these hacks one by one-

Combine some Plants

Increasing Plant density is a great solution if you can’t keep the humidity up in grow room or tent.  

Plants release vapor as a part of their respiration. With increased plants, your grow tent will get increased vapor. As a result, your grow tent RH will boost up.

As you’re a bit low on the budget, try to get some big plants.

Bigger plants have a lot of bigger leaves. Those leaves release a humongous amount of water vapor and CO2. Both of these byproducts help out younger plants.  

But if you overcrowd the grow place with bigger plants, then younger plants won’t get enough share of the nutrition and air flow.

Increase Watering

Here the trick is to keep water in the drainage system.

With excess water on the drainage system, your grow tent will see more water surface. Which will eventually, show you how to get the humidity up in grow tent through controlling irrigation.

But don’t get carried away. Increased watering might take out your plant for good. Also, keep in mind that your water bill will increase more than average.

Hang Wet Towels

By now, we know that more water surface means more humidity.

So, a clever way to create more water surface is through this method. Get some hangers and hang around wet towels inside your grow tent or room.

For a grow tent of 4×4 feet, 2 wet towels would be enough. Also, while hanging the towels, check that it doesn’t hamper air flow.

Soak the towels in the morning and hang those on the first day. Check every two hours to see when the towels dry up. If the towels dry up fast, then it means the air lacks humidity.

According to the Penman-Monteith equation, the average drying time of a towel is 4 hours. If your towel takes 4 hours or less time to dry up, then add up more wet towels.

This is a great way of controlling grow tent humidity indeed!

Spread Around Water Sources

This is a cheap hack and is used by many growers.

Here the goal is to place water trays inside the grow place. The philosophy behind this is the same as before.

Which is- Increased water surface = Increased Humidity.

So, handpick some optimum spots inside the grow room. Some great spots are- close to an air intake tubing and other passive air holes.

You can also put wet sponges beside every grow tray. This will increase humidity levels near your grow plant.  

Phase 3: Products to Raise Humidity in A Tent

If you’re here, then most probably the previous phases failed. There are two probable reasons behind this failure-

  • Your grow place has severe dryness
  • Your grow place is too big, and those hacks aren’t covering enough area

So, it’s time that you opened up your wallet to fix this humidification issue. The methods explained in this phase are the best way to raise humidity in grow tent.

Now, let’s explore the ‘possible futures’ of your grow place-

Add up an Air Conditioner

If the existing air conditioner isn’t enough for your grow room then you either have to replace it or add up a new one.

This time properly calculate the AC Unit you need for cooling down your grow place. If you are adding up a new AC, then calculate how much combined-output you will need.

Based on the calculations add up a new AC or replace the old one.

Change the Floor Soil

Yeah, you heard it right. Soil has it’s role to play on bringing down the humidity level too low. So, how to add humidity to grow tent just by changing the floor soil?

Here’s how it’ll work-

  1. Choose a soil with better water holding capacity
  2. Make a pathway or flooring with this soil
  3. Create a massive area of water surface

As a result, your grow tent or room will see a rise in RH.

As this new soil must hold water in a significant amount we must choose carefully. We know that in case of holding water-


But using a fully Clay based flooring isn’t a good idea. You don’t want your grow-place to become a sticky swamp. So, use a mix of Clay and Slit for this method.

Just to be clear, this floor soil isn’t your growing medium. Your grow place might have plants in growing trays or in soils.

If your plants are on soil, on the ground then this becomes a bit complicated. In this case, you don’t have to change the whole growing medium (soil). Just give the grow place a pseudo flooring with your soil mix.

Create your own Propagation Set-up

Here the trick is to raise the RH by extracting a cool mist into your grow tent.

For this method, you need an Adjustable extractor + Built-in thermostat. This extractor controls temperature by pulling out air.

Now, for the installing part,

Start off by placing a bucket of water, on top of your grow tent. This water will be transported into your humidifier through a hosepipe.

Soon, you’ll see a cool mist entering into your grow tent.

Install a Humidifier

Buy yourself a humidifier and get rid of all this humidifying mess.

If you already have one then make sure its dial is in between 50% to 65%. If your humidifier has a humidistat, then you don’t have to worry about turning it off.

But if it doesn’t have one then you have to be careful. If a humidifier runs constantly in a confined space, then it will increase the RH to an extreme level. Therefore, your grow plants will suffer extreme consequences.

So, get a good humidifier or use your grow room humidity meter to check RH level timely.

Special Scenarios

We have talked about raising the humidity in three simple phases. First trying out the free methods, then through low budget hacks and then through the expensive yet effective methods.

Now, we’ll suggest to you what to do in special scenarios. These suggestions include season specific suggestions and growth-stage specific suggestions.

We will discuss which humidity level is better for which special scenario and how to get those.  

Raising Humidity in Different Seasons

Humidity level doesn’t stay the same during all the seasons. So, we’ll bring about season specific details about raising your grow tent humidity level.

Summer: In summer the humidity is high. So, you may not need extreme methods for this. A few hacks would be fine.

Just make sure your grow-place temperature remains between 18-22 degree Celsius or 64-71-degree Fahrenheit. The humidity will adjust on its own.

Start implementing the first phase. After implementing each method, check if your grow room humidity is above 40%.

Use an extra air conditioner or a bigger one if the temperature raised too high.

Fall: In fall the temperature gets cooler every day. If you notice your grow tent humidity level is dropping in the Fall, then simply go through the first phase.

If the first phase doesn’t work properly then start implementing the 2nd phase methods one by one.

Just keep the RH and temperature in line with your grow stage.

Winter: Winter is the driest season. If you’re not prepared, then one winter can bring your plants down.

So, during winter be ready to implement even the 3rd phase methods. Just keep the temperature and RH suitable for your plants. You might also need low temperature recovering during winter.

Spring: In the spring, both RH and temperature start rising. So, if your grow room humidity level drops during this time, then go through the phases again.

There isn’t any ultimate set of methods specified for this season. So, it’s better if you go through the phases while checking your grow tent RH.

Raising Humidity in Different Grow-stages

Don’t follow blindly the average RH and temperature level for your grow-plants all around the year.

Plants need different humidity levels and temperature levels during different grow stages. Even the daytime and nighttime humidity in the grow room are different.

So, let’s get a quick look at perfect grow-room humidity percentage for different growing stages.

Grow Stages Clone Vegetation Flowering End of Flowering
Humidity Level (RH) Without Roots: 80-100 %   50-60% 40-55% 40%  
  With Roots: 60-65%      

We believe that this chart makes everything clear. So, you can raise your grow place RH level targeting the limit of this chart.

Just like before, check how much RH you’ve managed to increase after using each method.

For example, let’s say you see that during the vegetation stage, your grow tent RH is at 30%.

After seeing the RH deficiency you’ve used the Wet towel hanging method. After some time, you see that this brought your RH to 40%. So, now you take help from another method. This time, you use the water tray method.

After a day or two, you find out that your RH is at 55%.

So, if one method doesn’t work then combine another method.

But if your RH raises more than the targeted amount, then you have to stop using the last method and then use another method.

Neither too High nor too Low

To get the best output, you must keep the humidity level in a sweet spot. This sweet spot is the perfect temp and humidity for grow room.

If you provide too much humidity, then plants will face outside problems. If the humidity is too low, then plants won’t be able to grow properly.

So, let’s explore 2 scenarios-

Too High Humidity Kills

Too high humidity will result in grow room condensation. As a result, your grow tent or room-

  • Will create the best environment for bacteria and mold growth
  • Will get bud rot or botrytis to your flowering plants
  • Will have the pest and disease threat level at a maximum
  • Will suffocate your grow plants
  • Will decrease the efficiency of your plants’ nutrient intake

Too high humidity will at least reduce your yield if not destroy your plants fully.

So, while raising the humidity level in your grow tent, be careful and don’t overdo. Lowering humidity in grow tent is a must if RH goes higher than average.

Too Low Humidity Kills Too

When the humidity is too low in grow room that isn’t good for grow plants at all. If the RH is lower than its optimum level in a certain grow stage, then your plants will face consequences.

What are the signs of low humidity in grow room?

There are three outcomes of low humidity in grow tents-

  • Your grow plant will draw water excessively from the grow medium. If the grow room humidity is too low, then your plant won’t be able to keep up with the humidity loss. As a result, your plant will close up its stomata and suffer growth halt.
  • As mentioned earlier, due to low RH, your plants start taking too much water through its roots. With increased water intake, your plants start taking an increased amount of nutrients. This extra nutrient is actually bad for plants. As a result, you’ll notice nutrient burn on the leaves.
  • Your plants will become weak and with time they may die because of low humidity level.   

Being scared of the high humidity level, don’t let the RH drop excessively.

Just keep the RH in a sweet spot.

Don’t Miss the Safety

We have laid out several methods in three phases. Most of these methods are DIY methods. So, it’s highly suggested that you maintain some safety measures while using those. Or else, a slight accident may result in severe penalties.

So, here are some safety measures that you should keep in mind-

  • While removing fluorescent lights, check if your plants are getting enough light. Or else this would be a bad trade-off.
  • While combining big plants with small ones, make sure that none of your plants are in the flowering stage. You may end up affecting your grow plant pollination
  • While hanging wet towels, make sure that you’re not covering light sources.
  • While establishing your own propagation set up, be extra careful with the electrical work. Dealing with electricity and water at the same time is pretty dangerous.
  • While using new soil as the flooring, use gloves. Also, after using the new soil, be careful while stepping into your grow tent. One slip and you might fall down on your face.
  • While using water-based techniques, keep track of how much water you’re using. You don’t want to get broke over water bills.
  • Keep electrical lines and water sources far from each other. To be more specific, do your wiring perfectly.

Raising humidity of a grow tent is a tough job. But it’ll become a lot tougher if you miss out any important safety measure and end up hurting yourself.


Question: What is Vapor Pressure Deficit (VPD)?

Answer: VPD or Vapor Pressure Deficit is the difference between AVP and SVP. AVP stands for Actual Vapor Pressure (in a certain space), and SVP stands for Saturation Vapor Pressure (in that same space).

Question: What is the difference between a humidifier and a vaporizer?
Answer: A humidifier, releases a cool mist by physically dropping tiny droplets into the air flow. On the other hand, vaporizers heat up water and release steam. Use a humidifier in a grow place.

Question: Will adding salt in humidifier be helpful?
Answer: Adding salt in a humidifier won’t be helpful as it sprays water.

Bottom Line

It’s been quite a journey. We hope that by now you’ve become the ‘Three-Eyed Raven’ of raising humidity in grow tent.

Without proper care, your grow plants won’t pay you back properly. So, don’t let your plants suffer from low humidity.

We’ve revealed the answers of –

How to get the humidity up in grow tent?

How to regulate humidity in grow tent?

Now it’s up to you to find the best way to raise the humidity in grow tent.

Follow this guideline and your grow tent or grow room humidity will reach the sweet spot in no time.

Happy Growing.

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