Create The Best Climate For Marijuana Grow Room

Once you’ve decided to grow your marijuana plants indoors in a marijuana grow tent, your next step is to figure out how exactly you are going to do it. There are a number of factors to consider when setting up your growing environment indoors.

Whether it’s the temperature or humidity of the room, the carbon dioxide level, the ventilation or the smell, you are going to have to arrange everything perfectly so you create the ideal environment for your marijuana plants.

Although this may seem like a huge amount of effort at first, it has a huge payoff once you harvest. The only thing you might regret is not researching or preparing enough ahead of time; if you put in the work ahead of time, your result will be well worth it. This article will cover the following key elements of creating and maintaining a proper growing environment for your Cannabis.

1. Light – Bright but not too bright


2. Temperature – Comfortable for you, comfortable for your plants


3. Air Circulation – Fresh air plus a gentle breeze


4. Reflection – Cover your walls with a reflective material


5. Humidity – Controlling humidity helps plants grow faster and can increase resin production

You need a great environment to produce the best harvest. A poor growing environment lowers both yields and bud quality!

Here are what I consider the key five steps to perfecting your grow room climate control.

1. Dial your light setup.

Light isn’t something growers overlook when they think about plant health and indoor grows, but there is one element that can get missed: Most lights add a lot of heat to the room, so you really have to include that consideration as part of your climate control. Lighting dovetails with temperature control, and you’ll have to think all of that through.

While some growers are moving to LED lights, many are sticking with tried-and-true metal-halide and HPS (or high-pressure sodium) lighting systems, which can add a lot of heat and elevate your room beyond the 20-degree or so window that most growers aim to stay within.  By the way, if you are a beginner, full spectrum LED grow light can be your great choice!

2. Think through temperature control.

Generally, that 20-degree temperature window I was just talking about—warm enough to not freeze your plants, cool enough not to fry them—is somewhere in the range of 65 to 85 degrees F. Because of lighting, most indoor growers usually only have to worry about cooling.

For hobbyists or growers who are just raising a few plants in their home, a simple window AC unit might be sufficient. Unfortunately, though, they’re not very efficient.

That’s one of the big things growers find out when they start to scale up; When they go bigger, some of those simple solutions fail. Window AC units don’t scale too well. When it comes time to scale up your operation, you’ll want to look at a system that functions more like what you’d call central air in a home environment.

3. Plan for keeping air moving.

Keeping air moving in your grow room serves two purposes: It helps with mold prevention and it helps build stronger stems and branches on your plants.

If you’re not familiar with transpiration, think of it this way: Your plants soak up water at the roots, and the water moves up through the plants. That water doesn’t disappear, it’s evaporated through small pores in the leaves. Circulatory movement of air within the grow room breaks up the boundary layer of air that, otherwise, would simply hang around your leaves, keeping them too moist and vulnerable to mold and fungus.

Oscillating fans are usually enough to keep air circulating, but if for some reason you want to do air exchange and bring outside air into your grow room – for instance, if you live in a dry environment and want to use exchange to keep humidity down – your solutions will be more complex.

4. Be prepared to control humidity.

Humidity control is really the primary climate control aspect of high-performance growing. Most people think of it as mold control, but another good reason to have a handle on your humidity is to influence your cannabis plants’ transpiration rates.

For humidity measurement, a handheld sensor may be enough to provide accuracy within about five percent. Larger grow operations are moving toward electronic monitoring systems that include sensors and will automatically record humidity and even take actions with fans and dehumidification equipment.

The problem with some of these solutions is that humidity is a deceptively complex topic. It sounds easy—it’s just water in the air. But when you start talking about relative humidity related to temperature and other variables, it’s not so simple.

Humidity control, overall, is one thing people miss particularly when they’re scaling up their grow operation, they don’t realize how much moisture each plant processes through itself. It gets to be quite a lot of moisture. In a small system, a small, residential portable dehumidifier that you buy at the hardware store will be fine, but once you get dozens or hundreds of plants, the way to handle that quantity of water is much different. Residential dehumidifiers won’t work as well and they won’t be as energy efficient as a commercial dehumidifier.

That’s why it’s a good idea to at least initially bring someone in or contact someone with some experience in that area to get you started.

5. Think about your CO2 levels.

CO2, or carbon dioxide, is the one nutrient that could be included under the umbrella topic of climate control.

Essentially, if a grower is using high-powered lights (generally higher powered than CFLs or fluorescents) and the plants are getting sufficient water and nutrients, they can use more CO2 than the environment can naturally provide. So, in the process of optimizing your growth environment, the CO2 level can actually be your limiting value.

Many high-performance growers shoot for 1,000 or 1,200 parts-per-million, whereas the average in the environment is around 400 ppm—though it’s on an upward trend of course. Like all the other nutrients, you can have too much or too little. The proper level varies from day to night and also depends on growth phase.

Many growers use compressed CO2 ; it’s an odorless gas. Generally, they have a valve and set a timer that turns the gas on for a fixed amount of time every so often. Or there are fully automatic methods with electronic sensors.

This is why it’s important to think through your whole grow process. If CO2 is going to be a limiting factor, you may want to build it into your climate control system, as well.

Your marijuana plant will respond to temperature changes differently based on their growing stage.  As a grower, you need to make sure your plants have the best temperature for the growing stage they are in. Below are some ideal temperatures for every stage of the growing process.

Clones do not have their root system yet, so they depend on transpiration for their water. Therefore, they require high amounts of humidity, at least until they have fully formed roots. Many growers use a humidity dome to create an ideal amount of humidity for clones.

The ideal temperature for clones is between 68-77°F (20-25°C) with high humidity. At these temperatures, they should quickly form roots and become more self-sufficient. These temperatures are similar for seedlings.

During the vegetative stage, young plants prefer a high humidity (70% or more) and temperatures between 68-77°F (20-25°C). However, as the plant gets older, a slightly lower humidity is okay. This is more of an issue for indoor grown plants, as outdoor grown plants are able to withstand more temperature fluctuations.

The ideal temperature during the vegetative stage is between 68-77°F (20-25°C) with moderate humidity while also providing slightly cooler temperatures during dark periods.

The cooler ‘night’ periods are perfect for encouraging growth. Don’t let temperatures drop below 59ºF (15ºC). Once the plant matures, it should be able to withstand cooler temperatures during the day and drier air as well.

Once your plant reaches the flowering stage, it can thrive at a comfortable room temperate with low humidity. Unless you are adding additional CO2 to your grow room, a temperature under 82°F (28°C) is ideal. These lower temperatures encourage potent, trichome rich buds that you can smell and enjoy before you burn them.

Don’t go over 82°F (28°C) because higher temperatures cause terpenes to evaporate and they also slow bud growth. If your buds are too hot during this time, you may be literally burning away the good stuff as they grow, leaving very little taste or smell by the time of harvest.

Be especially careful to keep it comfortable for your plant after week 6 or 7. This is when terpene production is at its max, and you risk evaporating them due to high heat.

For optimal trichome production, make sure it is slightly cooler during the dark periods. The change in temperature may trigger increased terpene content as it optimizes plant processes. Just don’t make it too cold.

This process leads to what is commonly known as the dew point. The dew point occurs when the air can no longer hold any more water vapor, and it condenses into droplets called dew.

If you aren’t familiar with terpenes, they involve much more than taste and smell. They also impact the color of both the buds and the entire plant. Terpenes are responsible for the tomatoes red color, and they possibly may do something similar in certain cannabis strains. With the proper dark-period temperatures, you can bring out interesting colors in your plants (such as blue, pink and purple).

This phenomenon depends on the strain, of course. Most marijuana plants only grow green buds, but if you want to see what your plant can do, keep it cool for it ‘night’ temperatures and find out.

Essential to profitability is making sure every plant is healthy. As plants absorb water and nutrients, they transpire (more so in higher temperatures) and can create a very humid environment that may welcome black mold, powdery mildew and pests. The Herbal Cure wards off such threats with fastidious climate control, using 110-pint dehumidifiers that help maintain 40-percent to 50-percent humidity. The goal is to create such a healthy environment that plants can defend themselves against almost anything.

Newman says commercial cannabis growers must be vigilant about conditions that create microclimates, such as a room set for 60-percent humidity and 78 degrees. “In that microenvironment, where leaves overlap and lay atop one another, there is no light, there is 100 percent humidity, and there’s a lot of extra heat-the perfect environment for mold spores to take hold.”

The Herbal Cure has taken home six first-place awards for traits such as flavor, yield and potency.

Good pruning can prevent such problems. When plants reach the flowering stage at The Herbal Cure, they are pruned until there is only one node on each branch. The idea is to create airflow beneath the canopy and prevent microenvironments. Pruning also forces a plant to direct all its energy into top growth where it gets the most light.

Newman believes in following recommendations provided by Vapor Pressure Deficit (VPD) charts, which prescribe the right humidity and room temperature during vegetation and the first three to four weeks of flowering. (Vapor Pressure Deficit measures the difference between the moisture level in the air and the amount of moisture the air can hold. Temperatures come into play since warmer air can hold more moisture than cooler air. Cannabis plants will try to cool themselves in warmer temperatures through transpiration, which further increases the moisture in the air.)

“When you start to see buds form and good resin production, drop your humidity down to 40 to 50 percent,” he says. “Anything above that encourages powdery mildew. Anything below it encourages downy mildew.”

Newman says the principles of humidity control are simple: If humidity is too low, moisture is drawn from the leaves, which stresses the plant. Too much humidity can ruin THC production. Plants may grow vigorously, but the resin content won’t be desirable. In a perfect environment, the humidity in the air is matched to leaf humidity, producing robust growth.

Controlling humidity also plays an important role in drying and curing—a process that can make or break a cannabis crop. “If you don’t have enough humidity, your flowers are going to dry too quickly, locking in moisture and chlorophyll,” he says. “You’ll get a harsh smoke that has no flavor.” On the opposite end, too much humidity promotes bud mold or rot, which can wipe out an entire crop.

Through trial and error, The Herbal Cure has developed a curing formula that Newman says delivers consistently good flavor and smoke: Harvest the plant, remove the largest fan leaves and hang it for 14 days at 65 degrees and 60-percent humidity.

Simple Principles to Follow

Newman says cannabis thrives when growers follow simple, well-honed cultivation principles, such as maintaining 40-percent to 50-percent humidity, avoiding cross contamination and making sure water has the right pH for plants to absorb nutrients. Veer from that path, and you start to have issues.

“At the end of the day, people often try to put their own spin on it, create their own version of cannabis cultivation and claim it as their own,” he says. “But really, if you just follow basic guidelines, you’re going to have a successful run, and you’re going to be a great grower.”

About the Author: Crystal Hammon manages Leading Reads, an Indianapolis company that helps companies create original online content and build relationships with their customers and friends.

Plants require airflow because all leaves develop a microclimate that is independent of the ambient climate that a plant is in. This phenomenon is called the boundary layer resistance and is largely influenced by air movement. Static or non-moving air, creates large boundary layers. This produces a microclimate around the plant that is increasingly different from the surrounding air. The boundary layer influences how quickly gasses and energy can be exchanged. The boundary layer resistance can become thick enough to impede CO2/O2 exchange, transpiration and thus photosynthesis and plant growth. As such it is important for any indoor environments to have at least some airflow to reduce the boundary layer resistance. It's important to have a great grow tent ventilation.

Plants require fresh Carbon dioxide to continue with photosynthesis, when plants utilize CO2, the concentration of CO2 in the surrounding air reduces, lowering the potential for a plant to continue with the same level of photosynthesis. To make sure that the ambient level of CO2 concentration is maintained, fresh ambient air, or air enriched with CO2 must be introduced. Fresh air, either from outside or indoors is a good source of air replacement. You can also get compressed tanks filled with CO2 which can help boost the natural levels of CO2 even higher and improve photosynthesis and yield. For more information on CO2, look for our tutorial, “When and How to Use Supplemental Co2”, coming soon!

It’s important to realize that there is no one “perfect” growing environment. Just like people, each plant is a little bit different and may respond better to some environments than others. For example, some plants can better handle the heat or cold, and some plants aren’t as picky about good air circulation. But by taking care of the 5 factors of a great cannabis growing environment, you will ensure that your plant will be comfortable no matter what the strain!