Creating The Perfect Climate For Growing Marijuana Indoors

Cannabis Growing Facility
Author avatar By Derek LaRose
July 21, 2020

For the many cultivators who are unable to grow marijuana in the great outdoors, growing cannabis indoors is the only option. Therefore it is paramount to know how to create the best climate for a grow room. Get familiar with the factors that make up the perfect setting, and watch your marijuana seeds flower and flourish.

There are five key aspects of climate control to keep in mind. Each one is just as important as the other, and they all should interact harmoniously to produce the ideal growth environment.

These are the five aspects of controlling the climate in which you grow cannabis plants:

  1. Provide proper lighting.
  2. Maintain the ideal temperature.
  3. Ensure sufficient airflow and ventilation.
  4. Take control of the humidity.
  5. Optimize carbon dioxide levels.

With careful planning and precise execution, your plants will be most comfortable and reward you with the highest possible yield.

Ready to learn more? Let’s tackle the five climate control factors one by one.

1. Provide the Proper Lighting

Plants are capable of manufacturing their food through the process of photosynthesis. Light is one of the primary ingredients required for this process. So choosing the best lights is very important. Your precious plants would need the sun’s powerful rays to make food from carbon dioxide (CO2) and water. The photosynthetic process takes place via the pigment chlorophyll, which gives leaves their green color.

For sure, you must provide artificial sunlight for the plants since you are growing indoors. But how much light and what type of lighting is best?

Different Types of Grow Lights

Technology has allowed us to replicate the sun for indoor growing, and we have come a long way from Edison’s little light bulb. Nowadays, we can choose from a wide array of grow lights. As a rule of thumb, more lights equal more heat, and some lights generate more heat than others.

Here is a rundown of the most common grow lights:

CFL Fluorescent Lights

Fluorescent grow lights were the most widely available in the old days. Generations of farmers and botanists have used them for indoor gardens and seed germination in colder climates. They are still used extensively today, especially for marijuana strains that are very sensitive to heat.

However, fluorescent lights can get quite expensive because you will need more of them to simulate the intensity of sunlight. Also, you would need an array of different types of fluorescents to achieve the full spectrum of natural light.

HID High-Intensity Discharge Lights

These powerful lights were designed for stadiums and arenas, and work very well for growing cannabis. An example of HID is the Metal Halide (MH). It produces the full-color spectrum that is present in natural light. MH lights are suitable for all phases of the plant life cycle. However, they are particularly great for foliage production during the vegetative stage.

Another type of HID light is the High-Pressure Sodium Vapor Light (HPS). They emit an orange-pink glow, which is the ideal spectrum for marijuana’s flowering phase. But, they can produce lots of heat, so some growers like to mix fluorescent lights with HPS in their setup.

LED Light Emitting Diodes

LEDs are more commonly used these days. They are low maintenance, last longer, and consume less electricity. In addition, they produce very little heat, which means you might not have to buy appliances (like an air-conditioner) to cool down the grow room. Although LEDs are more expensive to purchase than other types of lights, they are more energy-efficient and cheaper in the long run.

High wattage and high lumen value LED lights work best. Also, check that they are capable of emitting the full-color spectrum needed for photosynthesis.

Proper Positioning of Grow Lights

CFLs and LEDs should be placed closer to the plants for maximum benefit. Adjust the position of the smallest and shortest plants, too, so that they receive sufficient light.

Metal halide and HPS lights should be placed farther away because they produce more heat than fluorescents and LEDs. You don’t want your plants’ leaves to get light burn! If some of the leaves start to turn yellow, add more distance between the plants and the lights.

For maximum efficiency, use reflectors. Reduce light loss by placing lights horizontally, not vertically, to make the best use of reflective surfaces. A beaten aluminum sheet can work as a reflector, as well as merely painting the walls white. Mylar foil is the most popular option for growers, and can easily be installed over the grow room’s walls.

2. Maintain the Ideal Temperature

Maintain the temperature in the grow room within the 65-85°F (18-30°C) range. When the grow lights are on (“daytime”), cannabis expects the higher end of 70 to 85°F (20 to 30°C). At “night” or when you turn off the lights, they prefer the lower end, 65 to 68°F (20 to 30°C).

The exact temperature depends on the growth stage of the plants:

Stage Temperature Range
Clones 70-85°F (21-30°C)
Seedlings 70-85°F (21-30°C)
Vegetative 70-80°F (21-26°C)
Flowering 65-80°F (18-26°C)

Colder temperatures can stunt growth and decrease blooming. Moreover, a sudden or prolonged cold spell could result in part of the plant or even the whole plant dying. Try to keep the temperature dip from day to night within a 10° window to prevent this from happening.

However, indoor growers are usually more concerned with too much heat. The presence of grow lights and ventilation issues can affect how high the temperature can get inside the room.

Excessive heat disrupts plant processes like photosynthesis and transpiration. It can impair root development and cause leaf drop. High temperatures could also encourage harmful organisms to proliferate, such as powdery mildew, mold, and spider mites.

Furthermore, high-temperature conditions can cause terpenes to evaporate during the flowering stage. Terpenes are essential oils that characterize fragrant and flavorful buds. They also provide the therapeutic benefits of marijuana by enhancing the effects of THC, CBD, and other cannabinoids.

Use air-conditioners or evaporative coolers to mitigate the heat. In choosing your appliance, take note that AC lowers humidity while an evaporative cooler raises it. Oscillating fans will help to distribute heat evenly, preventing extreme hot or cold spots within the room. However, they will not work to lower the temperature.

3. Ensure Sufficient Air Flow and Ventilation

A gentle breeze inside the grow room has two significant benefits: It promotes stronger branches and stems on your plants, and inhibits the growth of mold.

Transpiration is a plant process wherein water is suctioned up from the roots and transported to the other parts of the plant where it is needed. Eventually, that water ends up in the leaves where the excess will evaporate through tiny pores called stomata.

If the air around your plants is stagnant, that extra moisture doesn’t dissipate. A nice breeze hastens evaporation, just like it does with wet laundry on a clothesline. Overly damp leaves are vulnerable to mold and fungus, so maintaining continuous air circulation is vital.

Electric fans will help circulate the air inside the room. You should aim for the leaves to be rustling softly, but not waving around. Do not point a fan directly at the plants.That can result in windburn – the leaves get droopy and curve down to form claws. Too much wind could prevent the leaves from fulfilling their normal processes, thereby affecting the plants’ overall health.

Besides moving the air inside the grow room, you might want to bring the outside air in, and let some heat and humidity out. Air inlets such as slots or holes should always be situated near the floor, but make sure to install a barrier to prevent pests like rodents from entering the room.

Meanwhile, the exhaust system is ideally set in the highest part of the room. An exhaust fan helps prevent heat buildup in a closed space, but be aware that the smell of the buds will also escape. Add a carbon filter to your exhaust system so that you will not attract unwanted attention from passersby.

4. Take Control of the Humidity

Controlling humidity is a crucial factor in indoor growing. Too much moisture in the air makes plants more susceptible to mold, fungus, and other pathogens. On the other hand, excessively low humidity will dehydrate the plants and increase stretching.

Stage Humidity
Clones 75-85%
Seedlings 75-85%
Vegetative (early stage) 60-80%
Vegetative (late stage) 45-55%
Flowering (early stage) 35-45%
Flowering (late stage) 30-35%

To measure humidity, use a hygrometer. A compact handheld device is usually accurate within a 5% RH (relative humidity) range and can do the job in a small area. There are many thermometer/hygrometer combo meters available in the market these days. Look for one that has a longer probe so that you can monitor the levels from outside the grow room.

There are different techniques to control humidity levels within a space. Because humidity is sensitive to temperature fluctuations, controlling the temperature is essential to achieve ideal moisture levels. Installing insulation could help maintain a constant temperature and therefore manage humidity. Likewise, fans and ventilation systems ensure proper air circulation, which prevents stagnant, humid air from building up too much.

Humidifiers and dehumidifiers are appliances that manipulate humidity. You can find such devices in the hardware store, but a portable one designed for a residence might have to be scaled up for larger grow operations.

Since the grow room is typically a small, enclosed place, it is more likely to have surplus moisture content in the air. Plants usually transpire (or “sweat”) 97% of the water that they absorb. Measure your plants’ water input, and from there, estimate how much water vapor needs to be pulled out of the grow space. Make sure to acquire a dehumidifier that can collect the required amount of moisture.

Controlling humidity requires daily monitoring and adjustment. Any dramatic fluctuations should be acted on immediately. That way, problems can be caught early or even avoided altogether.

5. Optimize Carbon Dioxide Levels

Plants need CO2 to manufacture food during photosynthesis, together with light and water. In an outdoor setting, air naturally contains an adequate amount of CO2, but indoors is another story.

If a grower is using high-powered lights such as MH or HPS, plants can consume more CO2 than is present in the grow room. Even if the plants are supplied with plenty of water and nutrients, optimum growth could be limited because there isn’t enough carbon dioxide.

Out in nature, air contains 300-400 parts per million (ppm) of CO2. In contrast, high-performance indoor growers must aim for 1,000-1,200 ppm.

Some cultivators use compressed CO2 to augment the grow room’s atmosphere, but setting it up can get expensive and complicated. That type of system requires valves, timers, and sensors, and is usually automated.

For most casual growers and hobbyists, such a complex setup may not be necessary. Having a reliable ventilation and exhaust system is usually sufficient to pull the required CO2 from outside into the grow room. Because CO2 is a dense and heavy gas, it tends to sink to the bottom, so be sure there are fans that will stir up the air and push the CO2 to where it is needed.

Remember: The ventilation and exhaust system must run continuously whenever the grow lights are on. Photosynthesis will quickly deplete the CO2 within the space, and the plants will stop growing!

You have just learned how the five climate control factors work together to make the perfect grow room. By providing the right amounts of light and carbon dioxide, your plants will maximize their growth potential. Adjusting temperature and humidity, and ensuring good air circulation will keep them in a blissful state. The result will be a bountiful yield that will make all your efforts worthwhile.

Maintain the Ideal Grow Room Climate for Optimal Results

Don’t get discouraged if your plants do not respond as expected to the environment you have created for them. Growing mairjuana Sometimes, it takes a bit of trial and error. With more experience, you will be able to achieve your growth goals. Just keep at it!

About the author: Derek LaRose

Also known as Kronic from The Cannabis Kronicles, Derek LaRose is a young ambitious cultivator and a staple educator for indoor cultivation.