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How to make humidity for cannabis seed

Indoor Humidity Control for Cannabis Plants

If you want to grow sticky, high-potency buds, your cannabis will demand attention to its many needs.

One need of the growing cannabis plant – that is commonly overlooked – is humidity.

Believe it or not, humidity is actually very important to your plant! Humidity will help determine your plants resilience against mold/mildew in addition to how much your plants need to drink. Getting it just right can improve plant growth and increase your yields.

Luckily, there isn’t much to learn, so you can be the master of humidity in your grow with very little effort! Today we will give you the information you need to have complete mastery over humidity and thus, give your plants a boost in production.

Why Humidity Matters To YOU

In all stages of cannabis growth your plants will have a constant need to intake water, and the amount of water they need fluctuates with the humidity in your grow room. When the humidity is high, cannabis plants use their leaves to absorb moisture from the air which causes them to drink less water from their roots. Conversely, when the humidity is low, they will pull more water in through their roots.

Since humidity changes how much water your plants drink, and the water you give your plants have nutrients in them, being in control of humidity gives you increased control over your plant’s nutrient intake.

But controlling humidity isn’t just about prevention…having the right humidity encourages strong, healthy, leafy plants with vigorous growth. In fact, growing with DWC (Deep Water Culture) / Bubbleponics during vegetation with the correct humidity can actually turn into a struggle to tame out-of-control plant growth!

Additionally, after your plants start making buds in the flowering stage and get close to harvest, you can manipulate the humidity of your grow area to get your plants to produce more resin (trichomes/glitter which contain THC and other cannabinoids) while preventing plants from being attacked by mold. High humidity can sometimes cause mold or bud rot – a grower’s worst nightmare for those fat, dense main colas.

Effects of Poor Humidity Management

We’re not out to scare you, but you should know what happens to a grow room with poor humidity management. We know how important humidity is because we’ve experienced every one of these problems firsthand!

White Powdery Mildew

White Powdery Mildew is a fungal disease that will shows up high humidity environments. This can be tricky since young cannabis plants flourish in humid environments. Luckily, you can stave off WPM by making sure there is proper airflow in your grow area; a small oscillating fan – even on the low setting – works wonders.

Bud Mold or Rot

Bud rot or mold is – in my opinion – one of the worst pains a grower can experience as a result of poor humidity management. Imagine harvesting a huge, dense main cola from your plant only to see the insides are totally white or brown with mold. Buds in this condition are unusable and 100% should be thrown away.

Nutrient Problems

Humidity is a factor that partly determines how much your plants will drink. If the air is dry, your plants will tend to drink more at their roots. If they’re already drinking more due to high temperatures, low humidity can cause them to drink a lot of water through their roots and uptake too-high levels of nutrients. If your plant takes in more nutrients than the plant can use, the leaves will begin to show yellow or burnt tips, which is the result of nutrient burn. Sometimes too-low humidity can cause other apparent nutrient problems.

Slowed Growth

Cannabis plants love higher humidity when they’re young, and lower humidity when they’re mature. To be frank, if they’re not getting these conditions, they may not be growing nearly as fast or healthy as they could.

Humidity Basics

Okay, so now you know why you need to manage humidity when growing cannabis, but you may not know what humidity you are aiming for. This chart is the quick-and-easy answer:

Humidity is actually a measure of how much water vapor is being “held” in the air. There are different ways to measure humidity, including “absolute,” “specific,” or “relative” humidity.

Most growers are talking about Relative Humidity or RH when they talk about humidity in the grow room.

Relative humidity measures how much water is in their air compared to the maximum amount of water that can be held in the air at that temperature.

Below is a quick reference for the major stages of the cannabis life cycle in regards to the relative humidity you are aiming for. We’ll go through them all in more detail


Optimal Humidity is 70% RH

Clones need time to develop a root system to intake water. Young clones are solely dependent on getting water through their leaves from the air and this is only possible with high humidity.

Maintaining high levels of humidity will dramatically increase the chances of clones rooting successfully, and will increase young clone growth.

This is why many growers use a humidity dome for new clones!

Young & Vegetative Plants (seedling to end of vegetative stage)

Optimal Humidity is 40-60% RH

Seedlings and young cannabis plants in the vegetative stage grow a lot of leaf mass in a great growing environment, and plants can sometimes grow foliage at a faster pace than the roots.

But the roots aren’t the only way your plant gets water. Leaves can actually pull water vapor directly out of the air, and higher humidity in the air allows the leaves to get more water to the plant if needed. Until your plant has fully developed roots, low levels of humidity in the air can cause growth to be slower.

The ideas is to create a comfortably warm environment that mimics springtime or summer.

  • Don’t give seedlings a humidity dome unless it’s very dry where you live. They need springtime conditions, but it can be easy to go overboard with seedlings (compared to clones which love high humidity).
  • The RH is too high if the plants are forming wet spots on their leaves even when they’re not touching each other
  • As seedlings get older and become young plants, they want the humidity around 50% RH
  • If the RH drops below 25%, the dry air tends to limit growth and cause nutrient problems to appear on leaves, especially for young seedlings. Some seedlings are fine, but other plants are particularly sensitive to humidity.

Humidity for flowering plants

Optimal Humidity is 40-50% RH

Ideally, the relative humidity of your grow room should be lowered to around 40-50% at the beginning of the flowering stage. As plants approach harvest, some growers lower humidity down below 40% or even less to force cannabis buds to produce more resin, though I’ve seen that can majorly stress some plants, so that technique should be used with caution. Definitely lower the humidity just a little at a time to see how plants react before putting your plants in an extreme environment.

By the beginning of the flowering stage, your cannabis plants have created a large root system to fulfill their water needs. They will still be able to take in water through their leaves, but maintaining a relatively lower humidity than the vegetative stage helps prevent molds or mildews from forming.

Mold is especially dangerous in the flowering stage because it can form on or inside your buds or colas without you knowing. If you find that you have mold growing in any of your buds, or buds are rotting from the inside, you should immediately throw all of the contaminated buds away. Bud rot can ruin entire harvests, so if one bud is infected thoroughly search your grow room for more. If you can’t lower the humidity and already have a rampant mold problem, the best choice might be to cut your losses and harvest immediately to avoid any other buds getting bud rot.

Even if the humidity is low, it is still important to have air moving over and around your plants. Small fans blowing over and under the plant canopy will help keep air moving so that wet spots don’t form around any parts of the plant.

Extra resin production

  • During the last 2-3 weeks before harvest, some growers will use a dehumidifier to drop the humidity of their grow area to between 40-45%. This not only prevents bud rot during the last few weeks, the lower humidity may stress the plant in just the right way to increase resin production. As a result, you harvest extra-potent buds with more sparkly trichomes. While this technique has not yet been proven to increase resin, many growers swear by it. Just be aware that lowering the humidity too much can cause stress to some plants (other strains react well).

Humidity for drying buds (early stage cure)

Optimal Humidity in the Drying Room is 55% RH (for beginners)

Keeping the humidity around the 50% range will allow your buds to dry, but keep them from drying too quickly.

This range is also optimal for preventing mold, so it doesn’t get any better for drying if you’re a beginner!

As an advanced drying and curing technique, some growers like to keep the humidity a little higher so buds dry slower (which could possibly increase the quality of your cured buds). Drying with high humidity is considered an advanced technique because drying must be done with extra care to prevent mold forming on your harvested buds!

It’s good to have air circulation in the drying area, but it’s recommended that no air is being blown directly over the buds to prevent them from drying too quickly. More information in the link below!

Learn how to dry and cure buds for professional results every time (no more guesswork!):

Temperature and How It Relates to Humidity

Temperature and relative humidity are closely related to each other.

Relative humidity is measuring how much water is “being held” in the air compared to the maximum amount of water that can be held at that temperature.

Warm air can “hold onto” more water than cool air. Plants will tend to thrive at different relative humidities depending on the temperature of the air. Once the air becomes too saturated with water, it will tend to form dew or films of water over leaves, which leads to mold.

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For those interested in learning more about the science behind this, there is a term used by greenhouse growers known at VPD, or Vapour Pressure Deficit, that roughly measures the temperature and relative humidity.

According to Wikipedia: “the ideal range for VPD in a greenhouse is from 0.45 kPa to 1.25 kPa, ideally sitting at around 0.85 kPa. As a general rule, most plants grow well at VPDs of between 0.8 to 0.95 kPa.”

When growing plants, temperature is just as important as the Relative Humidity (RH) of the air, if not even more so! You need to control both temperature and RH at the same time to get the best results when growing cannabis.

  • If the air is too hot and dry (high VPD), plants will tend to have stretched growth.
  • If the air is too cool and humid (low VPD), plants are more prone to problems with mold or fungus.

Here’s what that means to you, the grower:

Cannabis likes a comfortable room temperature, or a little warmer – not too dry, not too humid. For most growers, that is all you need to worry about.

If your grow room feels warm or cold, humid or dry, that is a sign that you may want to look into changing the temperature and/or humidity of your grow area.

Generally, cannabis plants prefer temperatures in the 70-80 °F (21-27 °C) range during the day when lights are on. When lights are off (or at night), cannabis plants are happy with slightly cooler temps.

What if it gets too cold?

Colder temps will tend to slow down growth. Temps lower than 60°F (15°C) can upset plant growth and freezing temperatures will shock or even kill a cannabis plant.

Can cannabis stand higher temps? What if my grow room is too hot?

Please note that too-high temps in the flowering stage will not only slow down bud growth and cause fluffier buds, but it will also tend to reduce the potency of your buds by causing some terpenes and cannabinoids to burn off. Keeping the grow room temperature under control is important in the flowering stage!

  • With bright grow lights (such as 600W HPS and larger), cannabis plants can thrive at temps up to 85°F (30°C) even with no CO2 enrichment, as long as there is low relative humidity and plenty of air movement.
  • Cannabis plants can thrive at higher temperatures, up to an ultimate max of about 95°F (35°C), in an environment with low humidity, extremely bright grow lights and enriched CO2 (above 1500 PPM) – this is not your average grow!
  • Cannabis prefers slightly cooler temperature at night (warmer night temperatures will tend to slow down growth – so you can use this knowledge and raise night temperatures to slow down stretching plants that are growing too tall too quickly)

How to Control Humidity in the Grow Room

Step 1: Get a Humidity & Temperature Monitor to see if you need to adjust anything

I like the Ambient Weather WS-07 Wireless Thermo-Hygrometer because it lets you remotely check the temperature and humidity from another room (don’t forget to get 6 AAA batteries).

Step 2: Refer to Chart

Ideal temps are 70-80 °F (21-27 °C) during the day (lights on) and 5-10 degrees cooler at night (lights off).

Refer to the following chart to determine if relative humidity is in the ideal relative humidity range:

Young plants (seedling to end of vegetation)

40-60% RH (if you see wet spots forming on the leaves, humidity is too high or you need to increase air circulation). Beware of white powdery mold in humid grow spaces!

Flowering plants (making buds)

40-50% RH (a little less humidity helps protect plants from mold – during the last few weeks of flowering, a lower RH can possibly increase resin production as buds approach harvest)

Step 3: Correct humidity and/or temperature that is too high or too low

Many indoor growers tend to deal with too much heat and high temperatures – this is because grow lights can get very hot, and cannabis grows are often confined to very tight spaces due to stealth or privacy concerns.

The relative humidity of your grow area depends mostly on where you live, and how you’ve chosen to construct your grow area. Many growers struggle with lowering their humidity, because the mass of leaves and vegetation in a small grow area tends to cause the humidity to go up.

Here’s how you can correct common cannabis problems with heat and/or humidity.



Humidity is too high – how to lower humidity

Dehumidifier – will pull moisture from the air in a small area like a grow room or tent – a good one can be hooked directly to a drain for very humid areas like the UK and other humid parts of the world, otherwise dehumidifiers will automatically shut off when full and you will have to manually remove the water that it collects from the air.

Increase ventilation (add a more powerful exhaust fan or otherwise improve your exhaust system) – this increases the total amount of airflow in the grow area. This strategy will only work to lower humidity if the intake air has a lower RH than the air in the grow room.

Avoid over-watering plants – soggy soil (or leaving extra water in plant trays sitting in the grow area) will tend to raise the humidity of the grow room

Consider slight defoliation – very leafy plants will tend to raise the humidity of the grow room, especially when there isn’t good ventilation or air flow.

Air Conditioner (some are portable, some ACs fit in your window) – tends to lower humidity (in addition to cooling the air)

Humidity is too low – how to increase humidity

Humidifier – will add additional moisture to the air, I like the evaporative type of humidifier because it also works to cool down temps slightly. Make sure you get a humidifier with a large holding tank (holds at least 6 gallons of water at a time). Those “one-room” humdifiers with a 1.5 gallon tank often need to be refilled several times a day.

This humidifier is an evaporative swamp cooler that holds 7 gallons of water at a time – great for hot, dry climates.

Swamp cooler – will cool down air while increasing the relative humidity; works best when humidity is too low and temperature is too high. Read how one user used a swamp cooler to control his humidity.

Temperature is too high (too hot) – how to lower temperature & cool things down

Increase ventilation (add a more powerful exhaust fan) – this increases the total amount of airflow in the grow area. This strategy will only work to lower temperature if the intake air has a lower temperature than the air in the grow room (if the air outside is hot, too, adding more ventilation won’t do much to lower the temperature)

Air Conditioner (some are portable, some ACs fit in your window) – in addition to cooling the air, an AC will also tend to lower the relative humidity of the air

Light Schedule – Consider having your lights turn on during the cooler parts of the day (for example some growers have their lights on at night, and keep lights off during the hottest parts of the day)

Temperature is too low (too cold) – how to raise temperature & heat things up

Insulation – Consider insulating your grow box or grow tent with something that holds in the heat

Bigger grow light – Get a bigger grow light to produce more heat within the grow space (and get plants to grow faster!)

Monitor temperature & humidity in your grow room!

I like the Ambient Weather WS-07 Wireless Thermo-Hygrometer because it lets you remotely check the temperature and humidity from another room (don’t forget to get 6 AAA batteries).

Monitor temperature & humidity even while you’re away!

Here’s a really simple solution that lets you check your temperature and humidity of your grow room in real-time, even if you’re not at home!

Buy an indoor/outdoor temperature+humidity sensor and display, such as the model listed above

Put the “outdoor” module in your grow tent or box.

Put the “indoor” display in front of a webcam (you may have one built into your laptop, or buy a cheap and easy-to-use one like the Logitech HD Webcam C310)

You could also put the “indoor” display near your desk for easy viewing, and then point a webcam at the display.

Install TeamViewer (it’s free for personal use) or you can also use Windows Remote Assistance (not as user friendly in the beginning, but a good choice).

You can now log into your computer from any other computer, open the program for the webcam, and see what your grow room stats are in real-time.

Thanks to Tokiehardo for this awesome tip!

Too Hot, Too Dry – Humidity Story from a Grower in Denver

I’m preparing things for my first grow and trying to make sure that I plan everything ‘right’ and I’m not surprised by too many things, and hopefully none too late to fix.

Humidity has me confused. I’ve seen sources saying the greater the humidity the better, some that say humidity makes no difference as long as the plant is hydrated, and some claiming nothing will grow if you’re not nailed at 45%.

The ambient humidity near Denver is pretty low – the room I plan to grow in sits at 20% on average. Is this too low for my plants to be happy?

This humidity is too low for healthy growth of cannabis plants. This grower decied to build something known as a swamp cooler: swampcooler.html

It moistens the air while keeping the temperature down, which can also be a problem in Denver.

Update from the grower: For anyone stumbling onto this in the future, the swamp cooler in the link above is friggin awesome. I have it connected to my intake ducting and it’s keeping the cabinet at 73F with 80F outside temps! I cannot downplay how great it works, but I recommend creating a way bigger reservoir, so you don’t have to refill it every 6-8 hours.

How to Increase Humidity in Your Grow Tent (10 Easy Ways)

It’s not very difficult to grow a cannabis plant. But if you want to grow that primo sticky icky that’s covered in crystals and produces a beautiful and strong high, you’ll need to get certain factors right to keep your plants growing at their healthiest and happiest. Temperature, nutrients, light cycles and more are easy to remember, but there is another consideration to keep in mind; humidity.

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Plants need very specific humidity levels to thrive, and they can range from strain to strain and even through the life cycle of a single plant. But knowing what humidity your plants desire is only a small part of the battle. The real challenge is matching the humidity in their environment to your plants’ preferences. In this article, we’re going to discuss how you can raise the humidity in your grow tent to keep your plants comfortable and ensure they reach their full potential.

Understanding Relative Humidity

Humidity seems like a fairly simple concept on the surface. How much moisture is in the air? But there are different ways to measure humidity. When it comes to horticulture, we’re going to be mainly focusing on relative humidity. So, what is relative humidity?

Relative humidity is the amount of moisture in the air relative to the ambient temperature. Air can hold different levels of moisture depending on how hot or cold it is. Hot air can hold considerably more moisture than cold air. Relative humidity is expressed as a percentage of the total volume of water that the air can hold at any given time, up to 100%. Once relative humidity reaches and surpasses 100%, it means there is more moisture than the air can hold. This results in condensation, dew, fog, and other forms of moisture.

  • Designed to ventilate hydroponic grow rooms, transfer heating/cooling, cool.
  • Dynamic temperature and humidity programming, with timers, grow cycles.

When the temperature drops but the amount of moisture in the air stays the same, the relative humidity increases because the lower temperature air is able to hold less total water than the warmer air, so that same volume of water represents a higher percentage of its total capacity. Likewise, if the temperature raises but the total moisture in the air stays the same, the relative humidity percentage will go down since the air is capable of holding a larger volume of water now.

Factors That Affect Relative Humidity

There’s a lot going on in your grow tent, and all of it can affect the relative humidity inside. Each of these factors affects it independently, but they also interact with each other.


As we’ve mentioned, changing the temperature of an environment will also change the relative humidity. In a grow tent, you have fans and lights that are helping to adjust the temperature. Lights produce heat, which can lower the relative humidity of the grow room. Not all lights create the same heat, though. Modern LED lights create much less heat than metal halide or high-pressure sodium lights. This means they’ll have less of an effect on the relative humidity of your grow tent.


Ventilation and airflow will have a large effect on the relative humidity of your grow tent. If the air is being exchanged too quickly then it can dry out and lower the humidity of the environment. But too little airflow means the air will stagnate and the humidity will rise.


Since humidity is a measure of moisture in the air, it makes sense that having more water in the environment would lead to a higher level of humidity. The larger your water sources and the more water present in your grow tent, the higher relative humidity levels you will experience.

How Much Humidity Do Cannabis Plants Need?

Now that we understand relative humidity and some of the factors that can affect the humidity levels in your grow tent, let’s talk about how much humidity your cannabis plants really need. Your plants will intake water through their roots mainly, but they’ll also absorb some of the moisture in the air through their leaves. This leaves their roots freer to absorb the vital nutrients they need to grow and thrive. But your plants’ humidity needs will change through their life cycle.


When your plants are first starting and they’re very small, their root systems are not developed enough to uptake loads of water. Hence, they’ll be absorbing a lot more through their leaves, so the humidity levels will need to be high enough for them to properly hydrate. For these young plants, humidity levels should be somewhere in the range of 65%-80%.

Vegetating Plants

Once your plants are out of their initial growth stage and they’re ready to start vegetating, you’ll need to decrease the humidity in your grow tent. At this stage, humidity levels of 55%-70% should suffice. Keep in mind, each strain has its preferences, so these numbers are just a range to get you started.

Flowering Plants

Now that your plants have made it through the vegetative stage and they’re ready to begin flowering, they’re going to be asking for even less humidity. When they first start flowering, you’ll be dropping the humidity to somewhere in the 40%-50% range. As they get later into the flowering stage, you’ll want to keep reducing the humidity in their environment until your about 30%-40% relative humidity by the time they’re ready for harvest.

Young plants, seedlings, and clones Vegetative stage Early flowering stage Late flowering stage
65-80% 55-70% 40-50% 30-40%
  • See also:7 Best Ceramic Metal Halide (CMH) Grow Lights – Reviews & Top Picks

The 10 Ways How to Raise the Humidity in Grow Tents

Now that we know what factors affect humidity and approximately how much humidity your plants will need at any stage of their growth, let’s discuss specific ways to increase the humidity inside of your grow tent.

1. Add More Plants

Plants “breathe” through a process called transpiration. Basically, they’re excreting water vapor through their leaves after absorbing it through their roots. Naturally, this transpiration results in rising humidity. Adding more plants to your grow tent will increase transpiration, and thus, increase the humidity of your tent. These plants don’t have to be cannabis, though. Any type of large plants will help increase the humidity.

2. Reduce Ventilation

Don’t remove your ventilator fans entirely, but try setting them on low. Your plants need fresh air and they need circulation, but too much airflow can dry out the air and your plants. Try reducing the airflow and let it raise your humidity.

  • Oscillating remote control tower fan: The Honeywell Quietset tower fan.
  • Quiet cooling: Honeywell’s QuietSet line of fans are quiet and powerful, so.

3. How to Increase Humidity in Your Grow Tent

It may seem simple, but hanging some wet towels near the air inlet of your grow tent is a great way to add moisture to the air. As the air passes over and through the wet towels, it will pick up the water in them and hold it, increasing the humidity level of your grow tent.

4. How to Increase Humidity in Your Grow Tent

Since plants in the first stage of their lifecycle require the most humidity to thrive, you need a way to keep them wet and happy. Luckily, propagators make this very easy. It’s like a small plastic dome that keeps all the moisture inside. You’ll see the water droplets forming on the lid as condensation; proof that your seedlings/clones are getting plenty of humidity.

5. Add a Humidifier

When we need more humidity in our homes, what do we do? We add a humidifier. Well, what works for us will also work for our plants. Adding a humidifier is a great way to instantly increase the amount of humidity in your grow tent. If your humidifier has different levels to choose from, you can even keep adjusting your humidifier to match your plants’ changing needs throughout their growth cycles.

6. Reduce the Heat

Hot air can hold more total water than cool air so, with the same amount of moisture in the air, a hotter tent will have lower relative humidity. By removing some of the heat you can raise the relative humidity. If you’re using several lights, try removing one or more of them to reduce the heat output in your tent and see how much it affects the humidity of your grow.

7. Spray the Walls of Your Tent

Using a simple spray bottle, spray the walls of your grow tent each day. When these water droplets evaporate, they will increase the humidity level of the tent. You can raise the humidity more by spraying more water or applying it multiple times throughout the day.

8. Use a Swamp Cooler

Swamp coolers add moisture to the air while they reduce temperatures. This results in more water in the air, plus a higher relative humidity from the decrease in temperature.

9. Add Water Sources

More water sources mean more places for moisture to come from. If you add a bucket of water or several small containers of water to your grow tent, there will be more water to evaporate, adding moisture to the air.

10. Cool the Tent Down

If you add an air conditioner to your grow tent, the decrease in temperature will result in an increase in relative humidity. This is a simple way to raise the humidity without adding any water. But be careful as plants may not like it if you make their environment too cold!


Throughout the different stages of growth, your cannabis plants are going to have different humidity needs. You’ll need to adjust the humidity levels in your grow tent to accommodate these changing needs if you want to produce the best buds and largest harvests. We’ve discussed how your plants’ needs will change through their life cycle, from needing high humidity as seedlings and clones, to their much lower needs during the flowering stages. We talked about relative humidity and what factors affect it. Finally, we covered ten different ways that you can increase the humidity in your grow tent right now. You could add a humidifier, use an air conditioner to decrease the temperature and raise relative humidity, or you can simply spray the sides of your tent with a water bottle each day.

How to make humidity for cannabis seed

Over the last decade, more and more states have chosen to legalize the sale of both medicinal and recreational marijuana. Even without national legalization, the U.S. marijuana market was worth $9.2 billion in 2017 and is projected to reach $47.3 billion by 2027, a growth rate of 514% over 10 years (source: Arcview Market Research and BDS Analytics).

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Investors are flocking to the marijuana industry, seeing it as one of the safest long-term bets in recent history. Many of them are directing their investments toward dispensaries rather than growers, according to Scott Greiper, president of Viridian Capital Partners.

As the number and size of dispensaries grow, so do consumer expectations of the quality of marijuana products and the availability of diverse and unique brands. As in the wine industry, premier brand names can command a price ten or more times that of an average product.

On behalf of their customers, dispensaries are looking for consistent quality and a range of products. So while the opportunity to run a lucrative and stable growing business has increased dramatically, there is more and more pressure for growers to produce a consistently high-quality product in order to turn increased demand into increased dollars.

Let’s Get Growing

What are the most important points of growing a consistent crop to build your brand? Again, borrowing from the winemaker’s metaphor, it’s all about what you’re growing, where you’re growing it and the conditions it’s grown under. Below, we’ll look at how to create the best growing environment, with a focus on humidity and temperature controls .

To start with, relative humidity is determined by how much water vapor the air can hold at a specific temperature. Warm air can hold more water than cold air, so the warmer the air is, the higher the relative humidity will be .

As you probably already know, after choosing a substrate (the material you’ll be growing your plants in/on), the strain(s) of cannabis you’ll be growing, lights, watering mechanisms and nutrients needed, the most important element of your day-to-day operation will be managing temperature and humidity.

Each stage of a plant’s life-cycle is prone to different needs. With the right equipment, these needs are easily managed when the focus is on keeping everything within the desired ranges and as constant as possible.

To get started, you’ll want to buy a hygrometer and a thermometer. With these tools, you can accurately monitor and then alter humidity and temperature conditions in an attempt to strive for repeatable quality levels time and time again.

Shop Humidifiers and Dehumidifiers

The Four Stages of Plant Cycle

Seedling Stage

  • Seedlings and clones like high humidity levels of 65-70%
  • Temperatures with lights on: 68-77 F° (lights off: 8-9 F° lower)

The increased humidity levels allow seedlings to take water in through the leaves while their root systems are developing.

Vegetation Period

  • Humidity levels can be lowered by 5% each week (acceptable range: 40-70%)
  • Temperatures may be increased slightly if desired.
  • Temperatures with lights on: 71-82 F° (lights off: 8-9 F° lower)

As the roots are now more developed, they’re able to perform most of the needed water uptake with evaporation through the leaves now cooling the plants.

Flowering Period

  • Humidity levels need to be lowered to 40-50%
  • IMPORTANT– Never above 60% humidity!
  • Temperatures with lights on: 68-79 F° (avoid high temperatures)

Late flowering (1-2 weeks before harvest)

While not strictly a necessity, the following can have a direct impact on yield, flavor and appearance:

  • Bring down humidity levels as much as you can: 30-40%
  • Lower daytime temperatures, and also increase the temperature difference (day/night)
  • Temperatures with lights on: 64-75 F° (lights off: minus 9-18 F°)

Adjusting Humidity Levels and Temperature

Depending on your lighting solution, season a specific crop is grown in (assuming year-around production), the outdoor air vented in (as it will vary in temperature and its own relative humidity), controlling temperature and humidity in your growing space will be one of the tougher challenges you will face on a day-to-day basis.

While it’s tough, just know that every grower working at a scale similar to you is going through this as well.

Ways to Lower Humidity

  • Run your existing tube vent on higher velocities or upgrade your air flow fans. This applies to both air exits in tents and the room it is placed in! Increase fresh/cool air supply.
  • Try to water your plants right after lights are switched on. The room will be cooler at that time and the immediate absorption will result in less overall humidity.
  • The most consistent option will be: Invest in a decent sized dehumidifier–small humidifiers don’t have large enough tanks to keep up with the demand.

Ways to Lower Temperatures

  • Increase the total airflow and air exchange in your growing room
  • A simple trick: “lights off” during the day — “lights on” at night
  • When you grow with High Pressure Sodium lights (HPS), consider using a cool tube
  • Install an air conditioning unit (AC’s will also lower humidity levels)

Raising Humidity

  • You can temporarily increase humidity levels by misting with a spray bottle
  • Keep the surface of the soil moist, but not wet
  • Hang wet towels/cloths in your grow room or put open water containers in it
  • The most consistent option will be: Invest in a humidifier with a large water reservoir (the need for constant refills makes smaller ones inefficient)

Raising Temperatures

  • Upgrade to a bigger grow light (more watts = more heat)
  • Place a heating mat at the bottom of your tent or grow room
  • Use a simple space heater with a reliable thermostat

Protecting Your Investment

Though it may be exciting to see the fruits of your labor as you begin harvesting, the work is far from done. Correctly processing your crop helps prevent any chances of it becoming damaged or rendered non-smokeable. Proper drying and curing are essential to minimizing the risk of mold contamination and it also greatly improves the taste when smoked.


On top of the need for specific temperature and humidity controls throughout the growing process, it’s worth mentioning that humidity level during the drying process is equally important to the quality of the final product.

Too much humidity in your curing space and you might be left with perfectly grown, but moldy cannabis. Nobody wants that; neither the individual user nor the dispensary buyer. Moldy cannabis is easily the fastest way to ruin your reputation as a reliable grower of high-quality buds.

Again borrowing from Royal Queen Seeds expertise, here’s a how-to on drying your valuable crop:

Wet Trimming versus Dry Trimming

The curing process breaks down chlorophyll remaining in the plant, resulting in a less-harsh taste. Remember: harsh buds are not quality buds. These procedures can enhance the shelf-life of a crop, which is highly important with a product like cannabis that isn’t afforded the addition of preservatives.

Wet Trimming

“Wet trimming” involves trimming as soon as plants are ripe. Remove individual branches and proceed to use sharp scissors or shears to precisely trim excess plant matter. As soon as the plants are cut down, the drying process begins. What’s immediately noticeable is how sticky and wet the buds are. While this is an excellent indicator of potential quality, it’s also a breeding ground for contaminants. Buds left in this state will almost certainly be ruined so it is best to act quickly to begin a controlled drying process.

Widely regarded as the preferred method, “wet trimming” offers the most control and quality assurance. It also has the added benefit of allowing you to collect the “sugar leaves” which contain lower cannabinoid levels and can be stored separately to be processed into edibles at a later time. Remember that “High THC; low Cannabinoid level oil” states list from before? This is where that product comes from.

Dry Trimming

This technique is usually reserved for growers with a large amount of plant matter and little time to process it. This involves cutting off branches and hanging them whole from drying lines. Once the plants are dry, they are then trimmed and processed. It is more difficult to achieve the neatness of a wet trim as sugar leaves will curl in toward the buds while drying. The agitation of handling a dried bud during trimming can also result in the loss of potent resin crystals.

Drying Room Conditions

Whichever method you choose for trimming your product, suitable conditions for your drying room are important. You’ll want a cool, dark environment with temperatures in the range of 59-71°F and humidity at or near 50% . Yes, even after the growing process is completed, you still need to be concerned with temperature and humidity.

The Drying Process

If you opt to use the wet trimming method, you will need to spread them out across a large surface area. Aeration is important so you’ll want to avoid setting the flowers on a surface like cardboard or newspaper as the buds will dry unevenly. Wire mesh or netted drying racks are more beneficial. This allows airflow to reach all sides and lessen the chance of moist air pockets. Make sure to allow yourself enough space to spread your crop out evenly with a small amount of space between buds for the best results.

You may be tempted to speed up the drying process but it has been shown that slow and steady wins the race. Rushing the process and exposing your crop to high temperatures will almost certainly reduce the quality, and result in diminished flavor and even potentially a “poor and uncomfortable high.” Good luck explaining that to your investors or to a discerning dispensary that has numerous growers vying for their shelf space.

Here again is the equipment you can use to help you attain these levels:

  • Air conditioner
  • Dehumidifier
  • Humidifier
  • Portable heater
  • Thermo hygrometer to measure temperature & humidity levels

Check on your crop frequently, approximately every three to seven days. They will become noticeably drier with each check. You’ll know your buds are properly cured once they can snap easily in your hands without any signs of stringiness. Any bendiness when twisting slightly will tell you there’s water still present and that they’re not ready to move to jars yet.

Find the Best Air Cleaner for Your Grow Room

Pure n Natural Can Help

Pure n Natural Systems specializes in the sale of commercial and industrial humidifiers, dehumidifiers, drying fans, air movers, and portable heating and cooling solutions. We have the equipment you need to make your growing operation a consistent success. And as we’ve already discussed, consistency is king.

That said, we are not experts in growing specifics or in the design of custom-growing spaces.

However, if you say you need to remove 50-gallons of water a day from the air in a warehouse setting, we can help!