How to maintain optimal conditions in your grow house
Lifestyle
Audio By Carbonatix
9:00 AM on Tuesday, December 23, 2025
By Logan Evans for Meritus Gas Partners, Stacker
How to maintain optimal conditions in your grow house
Optimal growing conditions are a crucial component of what enables modern agriculture to continue delivering efficiently. As commercial growing needs evolve, having an alternative to open-field farming that allows you to control the microclimate and growth of crops or cannabis without seasonal or climate-related concerns is essential.
Well-optimized grow houses can contribute to year-round crop production and help develop faster growth cycles for healthier plants. For these reasons, learning to create and maintain a suitable environment for plants that offer high yields is important.
Here is Meritus Gas Partners‘ guide on how to maintain optimal conditions in your grow house, which elaborates on the science behind creating ideal grow house conditions and how to control the environment to ensure maximum yield.
What Are the Best Conditions for a Grow Room?
Understanding the best conditions for a grow room requires some basic knowledge about controlling the room’s environment. The ideal conditions for a specific grow room will depend on growth stages and the type of plant being grown. However, the key environmental factors to achieve the best conditions will always revolve around the following aspects:
- Light
- Temperature and humidity
- Carbon dioxide (CO2)
- Air circulation and ventilation
Exploring Each Element of Your Grow House Environment
Optimal growing conditions are an important balancing act to get right. It can provide plants with an environment that encourages growth by replicating the conditions that help them thrive in their natural habitat. For grow houses, achieving this means exploring ways to replicate each important environmental factor indoors to cultivate those ideal growth conditions.
Below are the critical factors that go into maintaining optimal conditions and how they can be achieved in a well-crafted grow house environment.
Light
Optimal growing conditions indoors require lights that can imitate sunlight. These are used for photosynthesis — a process that green plants use to convert light, water and carbon dioxide into chemical energy, releasing dissolved oxygen in the process. To achieve photosynthesis, your plants will need to grow under a specific light spectrum, which mainly consists of blue and red light.
While different plants and phases will need a varying degree of intensity and length of time, the growing stages and type of light required for an optimal grow house environment are below:
- A plant’s seedling stage: Plants need blue-spectrum lights to increase photosynthesis and strengthen root development. Blue lights with a wavelength of 400-500 nanometers will achieve these needs and help the seedlings grow.
- A plant’s vegetative stage: Plants in the vegetative state will need both blue and red light spectrums to encourage leaf and stem development through photosynthesis. Red light wavelengths can range from 600-700 nanometers.
- A plant’s flowering stage: At this stage, plants will need a red or orange light spectrum to stimulate bud growth and plant maturation. For optimal indoor growing conditions, flowering typically occurs once you change your lights to 10-12 hours of darkness, allowing your plants more time to produce buds uninterrupted in the dark.
Maintaining Optimal Conditions With Grow Lights
To reap the benefits of optimal indoor growing conditions, it’s important to have the equipment to achieve these outcomes. Investing in quality grow lights is an effective option to create those ideal growing conditions. Look for an efficient, low-heat output that can provide your plants with the full spectrum of light.
Popular grow light options include:
- Light-emitting diode (LED): LED grow lights are slightly more expensive than other options, but they offer a longer lifespan and lower operating costs. This can make them a more cost-effective solution in the long run, especially if you’re serious about creating ideal environmental conditions for plant growth. Many LED grow lights will cover the entire spectrum of light during the growing process.
- Light-emitting ceramic (LEC): These high-intensity lamps are also known as ceramic metal halide (CMH) lights or ceramic discharge metal halide (CDM) lights. They use arc tubes made of ceramic to operate at high temperatures.
- High-pressure sodium (HPS): These discharge lamps are commonly used in streetlights, allowing electric currents to travel through an industrial gas containing sodium, xenon and mercury. This process generates light. HPS lights are especially strong in the red/yellow light spectrum, which is ideal for plants during their flowering stages.
You can cultivate optimal growth conditions by using the right light source and embracing innovations to keep you on track. Using automated timers and controls to monitor and adjust light cycles during each growth stage can maintain the ideal light environment for your plants.
Common Grow House Lighting Mistakes to Avoid
Light choice, placement and distance are crucial in creating an ideal light environment for cannabis plants to thrive and produce a high yield. Avoid making these common mistakes in grow house lighting to save wasted costs and work hours:
- Choosing the wrong light: The spectrum of light available in your choices is important. The right balance of light to support each stage of growth can be the difference between success and failure. While many LED growth lights now offer modes that can easily switch between your desired stage of growth, growers may still be swayed by less expensive, poor-quality light options that fail to meet optimum growth standards.
- Incorrect height placement: If you place your lights too close to your plants, they can become damaged or burned. Putting them too far away means they won’t properly photosynthesize. While you should refer to the manufacturer’s guidance, LED lights may work under the following growth stage and distance combinations: seedling (24-36 inches), vegetative (12-24 inches) and flowering (12-18 inches). For high-intensity discharge (HID) lights, combinations may include: seedling (32-48 inches), vegetative (18-40 inches) and flowering (12-28 inches).
- Overwatering after changing light options: HID lights have higher water demand than LED grow lights due to the heat they generate. Growers who switch to LED lighting often forget to adjust their irrigation needs to accommodate this swap, leading to excess moisture and potential pest or root issues.
Temperature and Humidity
Planning how to control temperature and humidity in a grow house is a balancing act. You can have the most expensive grow house setup in the world, but it won’t deliver without a dialed-in combination of optimum temperature and humidity levels.
A grow house will only be as good as its environmental conditions. The overall temperature and humidity of your grow house have a direct impact on plant function in the following ways:
- Temperature: Temperature affects both photosynthesis and respiration by dictating its rate of chemical reaction. A low temperature will produce a slower rate of chemical reaction and plant growth, as the enzymes in the photosynthetic process have less kinetic energy. This leads to fewer collisions with substrates, which in turn reduces plant growth. High temperatures will cause enzymes to lose function, significantly reducing the rate of photosynthesis and potentially killing the plants. It will also increase the plant’s respiration and cause faster consumption of stored energy.
- Humidity: This affects photosynthesis through water evaporation (transpiration) and the open/close ratio of pores on your leaves (stomata). A dry humidity level will reduce a plant’s intake of carbon dioxide, which can slow plant growth. Dry air will also cause plants to shut their stomata to reduce transpiration loss. A humidity level with heavy saturation will slow down transpiration and reduce the amount of nutrients from roots to leaves. It will also create a moist environment that invites fungal disease and mold.
While ideal conditions will also depend on the growth stage of your plants, it’s essential not to overlook the interconnectedness of both temperature and humidity in an optimal growing environment.
Maintaining Optimal Temperature and Humidity Conditions
The ideal temperature range for cannabis is between 77° and 86° Fahrenheit. Exceeding this range can impact everything from potency and flavor to plant health. While each grow house will vary depending on setup and specific needs, below are some good rules of thumb to maintain optimal conditions throughout each growth stage:
- Seedling stage: A temperature around 72-78° Fahrenheit (lights on) and 65-70° Fahrenheit (lights off) with a relative humidity (RH) of 70%-80%. These temperature and humidity conditions help nourish seedlings and encourage root growth.
- Vegetative stage: An RH level of 45%-60% (aim to slowly decrease this as your plants mature) and temperatures ranging from 75-80° Fahrenheit (lights on) to 65-75° Fahrenheit (lights off). These conditions help plants at this stage continue to develop stronger root systems while growing faster.
- Flowering stage: Aim for a temperature of roughly 75-80° Fahrenheit (lights on) and 65-75° Fahrenheit (lights off), and an RH level of 40%-50% for the first few weeks, and then change to an RH level of 30%-40% with temperatures around 70-78° Fahrenheit (lights on) and 60-70° Fahrenheit (lights off) for later flower stages.
Common Temperature and Humidity Mistakes to Avoid
The biggest mistake a grower can make is to ignore the conveniences and appliances at their disposal. Understanding how to control temperature and humidity in a grow house is about working smarter, not harder. Temperature and humidity levels can be set and controlled through appliances that reduce the chance of your environmental conditions being compromised.
These appliances include:
- Dehumidifiers: These help remove excess moisture from the air, which can contribute to a grow house that’s free from mold, mildew and condensation.
- Humidifiers: These add moisture to the environment. They work well for grow houses with a relative humidity that drops due to cold weather.
- Hygrometers: These devices are cost-effective and measure the current humidity levels in a specified area.
The second biggest mistake to avoid is ignoring the benefits of vapor pressure deficit (VPD) measures. Many growers avoid this subject as it can seem overly difficult to understand. However, it’s essentially a way to track how much moisture the air wants to take from your plants. Too little moisture means a weaker transpiration and reduced nutrient intake. Too much moisture means a higher water demand for your plants.
Optimal VPD levels contribute to a good balance of transpiration and CO2 intake, which helps increase photosynthesis. A typical range for optimum growth efficiency will be around 0.45 to 1.25 kilopascals (kPa). If you’re unable to track VPD, being strict about temperature and humidity levels will ensure that you stay within these measurements.
Carbon Dioxide
Carbon dioxide plays a key role in photosynthesis. Being able to raise CO2 levels in a well-maintained cannabis grow room can help create faster, healthier buds. While carbon dioxide is an important part of the entire growing process, implementing a CO2 enrichment strategy during the vegetative stage and early flowering stage is where you’ll see the most benefits.
A CO2 level between 600 and 1,000 parts per million (ppm) during the vegetation stage will support a faster rate of photosynthesis, while a general CO2 level between 1,000 and 1,300 ppm should be your goal during the flowering growth phase.
Maintaining Optimal Carbon Dioxide
Carbon dioxide primarily benefits grow house environments through photosynthesis. However, studies also show that elevated CO2 concentrations contribute to reducing stomatal conductance and enhancing water use efficiency in plants.
But what are the best conditions for a grow room that needs CO2 beyond the naturally occurring levels? To maximize the benefits of accelerated growth and potentially higher yields, supplemental CO2 should be used in conjunction with high-quality, powerful grow lights and temperature monitoring to create a higher-intensity — but still optimal — growing environment.
This involves finding a trustworthy and consistent source of high-purity gas. Common solutions for this need beyond CO2 enrichment include:
- Hydrocarbon extraction: This solution employs a method that uses butane (C4H10), propane (C₃H₈) or a combination of both to separate cannabinoids, such as cannabidiol (CBD), tetrahydrocannabinol (THC) and terpenes. This method separates the compounds that contribute to the flavor and aroma of cannabis without altering their structure.
- Propane: Low-emission propane can be used to maintain consistent heat in your grow house. Its versatility means it can power multiple things, including maintaining an optimal grow house temperature.
Common Carbon Dioxide Mistakes to Avoid
Professional grow houses tend to use CO2 for plant growth, but they will also have strict detection equipment that monitors carbon monoxide (CO), propane, ammonia (NH3) and methane (CH4). One of the most critical mistakes to avoid is exceeding safe CO2 levels. Not only does it damage your plants, but it can also be very unsafe for workers.
Ensure that you have both fixed and wireless systems in place to detect issues and closely monitor safety levels.
Air Circulation and Ventilation
Strong air circulation and ventilation do more than properly distribute CO2. They also help maintain consistent temperature and humidity levels. Additionally, they contribute to a healthier grow home ecosystem that strengthens plant stems and prevents pests from damaging your plants.
For robust air circulation and ventilation, growers will need a combination of oscillating fans and carbon filters:
- Oscillating fans: These fans help maintain air movement in a grow house. By mixing the hot air and cold air in a chosen area, oscillating fans create a more uniform temperature. This promotes better airflow, aiding consistency in plant growth.
- Carbon filters: These help eliminate unwanted air and reduce the smell within your grow room. Exhaust fans will remove necessary air until humidity levels are consistently where they need to be, while carbon filters absorb the smell.
Regularly exchanging the air in your grow house is a vital part of replenishing CO2 while removing any excess heat and humidity.
Maintaining Optimum Air Circulation and Ventilation
Airflow makes a difference in your environmental conditions. Indoor growing plants, especially cannabis, can be crowded and overlapped. Having a wide selection of fans to remove any unwanted areas of excess humidity (called microclimates) is important. However, this may still lead to uneven conditions based on plant spacing and the size of your grow house.
To reduce this issue, it’s a good idea to calculate the cubic feet per minute (CFM) of your grow house. Just multiply the room’s length, width and height to determine its volume, and then multiply your volume by the air exchange rate you’re looking for. This gives you the base CFM requirement.
Finally, add percentages to increase your base CFM — 25% for each carbon filter you have, 30% for each 90-degree duct bend, 15% for each 45-degree bend, 1% for each foot of ducting and 10% for every light. After you’ve added those percentage increases, you have your final fan rating.
Common Air Circulation and Ventilation Mistakes to Avoid
Achieving the best possible control of your grow house environment is about understanding what’s available to make the process work best for your specific needs. Some common air circulation and ventilation mistakes to avoid include:
- Shunning convenient automated systems that can work in tandem with dehumidifiers and CO2 emitters to improve efficiency and response times.
- Confusing healthy airflow with a strong airflow that causes your plants to sway and move (gentle air movement is just fine).
- Placing fans in areas that will create microclimates or dry leaves when placed directly in front of plants.
Conclusion
A combination of the essential equipment for optimal grow house conditions and a clear idea of your goals can make all the difference. Having the tools and knowledge to cultivate a more controlled environment can deliver a higher yield, a healthier growth experience and a more enjoyable, less stressful growing process.
Temperature, light, humidity, CO2 and airflow that work together as one cohesive unit is the true mark of good grow house. When done consistently, great environmental conditions will be a natural outcome of any crop.
This story was produced by Meritus Gas Partners and reviewed and distributed by Stacker.
