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Greg the Alien is here and at it again! Sunlight and grow lights provide vital light for your cannabis plants to grow from seedling to harvest. These light sources can also add a lot of heat and humidity to any outdoor or indoor grow. Controlling and managing temperature and humidity effectively will ultimately impact the quality and quantity of your final harvest.
Humanoid scientific studies have done their best to confirm the ideal range for both, but there is no clear consensus due to several different variables [1]. However, finding a comfort zone for optimal conditions can still be manageable with the right environment and equipment. Whether you’re growing feminized cannabis seeds, autoflower seeds, or high-THC strains, managing your environment is one of the biggest factors in maximizing yield and potency.
Cannabis plant development depends on optimal temperature and humidity to process numerous internal functions vital for success. Learning how to manipulate both factors makes the difference between a high-quality, bountiful harvest and a cannabis plant full of bud rot and underdeveloped flower buds. Temperature and humidity control issues in either extreme range are important to control; however, so are air circulation and ventilation. This is especially true when growing premium cannabis genetics in controlled indoor settings.
Temperatures that are higher than the average range affect plant development by creating weaker buds in both potency and overall appeal. When I get too close to the sun in my spaceship, it can make me sweat and feel stressed—your weed plants aren’t any different!
High temperatures can create heat stress, which affects plant, terpene, and cannabinoid development and potency, while also causing nutrient burn and root rot. Low temperatures also slow down plant growth and create an environment for harmful mold, mildew, and bud rot. Growers working with rare cannabis strains or CBD-rich cultivars may find these temperature swings especially damaging.
Transpiration is essentially the process by which your cannabis plant sweats during development. It’s an essential process for photosynthesis and for moving nutrients and water from the roots to the rest of the plant while cooling it down. However, a major side effect is that a good amount of water vapor gets put back into the air as a result, causing increased humidity in a grow room or tent. [2]
Cannabis plants with excessive humidity have insufficient transpiration, which can lead to root issues, mold, mildew, and other plant diseases. Low humidity is often responsible for nutrient burn due to excessive water evaporation from leaves. This is why indoor growers who source their seeds from a reputable cannabis seed bank should also invest in quality ventilation systems to protect their genetics.
Growing cannabis outdoors can be an advantage due to the natural breeze and open space that allow for optimal air circulation and ventilation, which are essential for plant development. However, some geographical regions can be too stagnant and just plain hot. Try some of the techniques below to achieve optimal results.
Space your plants away from each other properly, so as not to overcrowd the grow area with too many transpiring plants not getting enough individual airflow. Be aware of the specifications of the specific strains you’re growing to space them correctly for all growth phases. This becomes especially important when cultivating large crops from bulk cannabis seeds.
Direct or create more optimal airflow naturally where open breezes occur, and there’s nothing in the way to block them. Create enough of a gap between all plants to avoid any issues.
Circulation fans aren’t just an indoor grow tool; they can also be used outdoors. Install oscillating fans to create a gentle breeze that keeps your plant foliage dry, thereby reducing the risk of mold and mildew issues. This can help ensure the success of outdoor cannabis seeds, especially in humid regions.
Use a greenhouse to maintain temperature, humidity, and proper ventilation, free of the often-overwhelming elements of the great outdoors. Keep doors and windows open for a steady exchange of fresh air.
Proper air flow and ventilation can often be thwarted simply by the very plant you are growing. When a plant has too thick and dense foliage, it’s necessary to prune and remove the excess. This will improve how air can circulate and be ventilated around your plants and grow area, while also helping to reduce moisture and humidity.
When growing indoors, avoiding mold, mildew, and a host of other detrimental plant diseases can be greatly achieved by maintaining proper air circulation and ventilation. This often requires additional equipment and costs on top of what you already have running in your grow setup. Indoor growers working with fast-flowering cannabis seeds or high-yield strains may find these investments essential for success.
As a crucial piece of indoor grow equipment, fans remove stagnant humid air while introducing fresh air and improved circulation. All of these fans, in conjunction with some ventilation ducts, will make a dramatic difference in maintaining proper temperature and humidity levels indoors.
Cannabis plants rely on different temperature and humidity ranges according to several different factors. Understanding how these affect your plant’s specific needs will greatly impact your success as a grower. Indoor and outdoor grows also have different variables to control—some are listed below; however, keeping everything within range is doable for both.
Okay, so you’ve probably been thinking to yourself, when is this little green SOB gonna finally say what the ideal temperature and humidity levels should be? For outdoor growers, much of the outcome is directly related to the geographical climate.
If you’re growing outdoors in a humid region like most of the East Coast, you’re going to have to make RH adjustments. The same thing goes for the PNW–be prepared for levels that can contribute heavily to mold and mildew. Desert environments are arid and dry and can use the aid of a greenhouse to help manage conditions and pests like spider mites.
Mitigate the elements of the outdoors with a greenhouse or plant covers. You can also use an overhead tarp to keep moisture under control from morning dew, excessive heat, and torrential downpours when necessary.
Researchers still have a lot of work to do when it comes to cannabis cultivation-based studies. Currently, there are only a few humanoid peer-reviewed studies that confirm the ideal indoor growing temperatures by stage. On the other hand, every single humanoid weed grower, big or small, has their specific ranges and preferences for their grows that they think are ideal.
To straddle the line of science and experience, I have included ranges according to researchers and ranges according to cultivation and light systems pros. I think it’s important to understand what growers versed in just how much grow lights add heat and stress to the environment think the adjusted ranges should be as well.
Vapor Pressure Deficit (VPD) is a factor that measures the rate at which plants transpire and how much moisture the air can still hold. By calculating the VPD, growers can ensure their plants are not only getting ideal temperature and humidity levels but also optimal results with the following:
VPD is calculated by measuring air temperature, leaf temperature, and relative humidity levels in an indoor environment. Overly humid air that contains a lot of water equals low VPD, while dry air that can hold even more moisture equates with high VPD.
Adding more humidity to a grow space will lower VPD, while lowering it raises VPD. Increasing temperature raises VPD, while lowering it lowers the VPD level. Circulation and ventilation equipment like that described for outdoor growing is also crucial to indoor growers navigating extremes in both ranges. [6]
Several cannabis researchers have reported a few slightly different windows of efficiency for temperature and humidity levels when growing cannabis plants. It’s up to you to be the judge of which ranges work for you and the specific strains and region you are growing in.
Some of these ranges are not as specific (day levels vs night levels), but according to researchers, growers should keep temperature and humidity levels in the following ranges for optimal VPD.
Seedling
Vegetative Stage
Flowering
Indoor Humidity and Temperature Ranges According to Industry Experts
According to Spider Farmer, an indoor cultivation household name, home growers should try to zero in on the following ranges and humidity for each development phase.
Seedling
Vegetative Stage
Early Flowering Stage
Late Flowering Stage
Dropping the temperature a few degrees at night provides a signal to your plants that the cooler overnight temperatures of autumn are on the way. This signal naturally occurs with outdoor grows, and helps indoor grows with flower, trichome, terpenes, color, and cannabinoid development. Lower nighttime temperatures also give your plants a rest while facilitating the metabolization of carbohydrates crucial to plant health. [7]
On top of implementing quality air circulation and ventilation equipment already discussed for outdoor use, such as fans and exhaust systems, there are a few other ways to stay on top of your indoor levels.
Hygrometers and digital humidity controllers are crucial for monitoring and adjusting humidity levels. Humidity controllers can automatically adjust your indoor grow space in conjunction with a humidifier/dehumidifier. Adjusting watering practices to avoid overwatering and excess moisture keeps humidity levels lower, while running your grow lights at night can help reduce extra heat in the grow area as well. Like outdoor plants, proper spacing and upkeep of pruning on your indoor plants will help with air circulation and lower humidity immensely.
Paying attention to your levels and ensuring your environment has what it needs to maintain balance and be successful is paramount in navigating the spectrum of potential that temperature and humidity bring to every grow. Understanding and applying many of these concepts to newer growers can be tricky, so always feel free to reach out to Uncle Paulie and the grow experts at Multiverse Beans with any of your indoor/outdoor temperature and humidity control questions!