Why Measure Temperature and Humidity?
Just like people, weed feels most comfortable when the temperature and humidity levels aren’t too low or too high. It grows best when it’s between 68 and 77 degrees F and between 40 to 70% humidity. Certain growth periods need a more specific range (but we’ll get to that in a minute). For best-growing conditions, you need a hygrometer and a thermometer.
[UPDATED August 2020] Welcome to this roundup of the Best Temperature & Humidity Controllers to monitor your grow room and make sure you are growing the best cannabis.
If you’re investing your time and money into raising cannabis, you’ll want to control grow room temperature and humidity to get the best harvest possible. When you grow indoors, you’re the boss of the environment. With the right tools, you can keep things in balance. Digital hygrometers and digital thermometers, and combination monitors, give you the information to precisely control your marijuana’s environment.
The best conditions for the best cannabis
You control the weather in your grow room. You can create the best conditions for your plants. We’ll get to how you can do that. Meanwhile, here are some guidelines.
Best marijuana growing temperature
The best temperature range for growing weed is between 68 and 77 degrees F. Also important for healthy cannabis, there shouldn’t be more than an 18-degree difference between daytime and nighttime temps or lights on/lights off. As we said, weed’s comfortable where people are comfortable.
If it gets too hot, like above 80 degrees, the plant growth may speed up but you’ll need to increase watering and fertilizing. It may stretch instead of focusing on growing big buds.
Keep your plants at the high end of the ideal range when they are vegetating, then drop the temperature to the low end for flowering and harvest.
Best humidity levels for cannabis
With regards to humidity or moisture in the air, cannabis likes it between 40 and 70%. Certain growth periods like more humidity than others, like sprouting.
- When you sprout seeds and have seedlings that are beginning to grow roots, give the plants 65 to 70% humidity.
- Once you have leaves and are in the vegetative stage, gradually lower the humidity each week by about 5% until the plants begin to flower.
- At flowering, keep humidity levels around 40 to 50%.
- Then about a week or two before you harvest, lower the humidity more, down to 30 to 40%.
Why do you need to lower the humidity as the plants grow? For a couple of reasons—One, too much humidity during the flowering stage can let your plants get moldy. You really don’t want moldy pot. Two, if the humidity hovers around 40% in the flowering stage, the plants will stay thirsty and drink a lot of nutrients and water. (But if you drop below 30%, the plants may react to protect themselves from dehydration. They will go dormant.)
Controlling Temperature and Humidity
Take a good look at your growing area. Is it a closet, a tent, or a room? Is it in a climate-controlled area like a bedroom or in something more exposed to the elements, like a garage? How much ventilation do you have?
If you use a grow tent, you probably have a relatively well-sealed-off area where you have good control over conditions. You may already have a fan or extractor setup, especially if you’re using hot lights like HPS.
And Don’t overlook How This Affects Your Home
It’s fine to ensure you are taking care of your plants but don’t overlook the potential effects on your home. Depending on where you are growing indoors the required humidity or the action you are taking to maintain levels may also affect the room itself, not to mention the distinctive scent given off by marijuana plants.
Many of the products listed below are equally suitable for maintaining appropriate levels of humidity in your home as well as in a grow room and will help to disperse the scent of your plants outside your home.
Heat Costs Money, So Cool It with LED Lights
HPS or high-pressure sodium lamps are great for growing weed, except for two things. They consume a lot of electricity and they make a lot of heat. You can hit over 100 F in a small tent with HPS lamps. If this is your setup, be very careful about monitoring the temperature and using the fan and ventilation system to keep things cool. Also, place your ballasts outside the grow tent if you can.
If you use LED lights, you’re wasting less power and you’ll have hardly any heat to expel. In fact, if your grow room is in a cold place, like a garage in the winter, you may need a space heater with a thermostat to help you warm it up. Always use a heater in conjunction with a shutoff temperature or you could roast your weed by accident while you’re out shopping.
We’ve reviewed a number of different grow room climate control options below. You’ll find simple hygrometers and thermometers; heaters and cooling; humidifiers and dehumidifiers; and full-featured grow room controllers. So, whether you’re on a budget or you’ve got money to invest, read on and you should find just the right grow room control solution for you.
Basic Hygrometers and Thermometers
The basic tools you need to control the environment in your grow tent or room are a thermometer and hygrometer. You can find good all-in-one digital hygrometer- thermometers for a decent price. If you plan to grow in the years to come, buy the best one you can afford. It will save you a lot of stress and probably some money, too.
We like the models below:
Extech Big Digit Indoor/Outdoor Hygro-Thermometer
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Extech is a trusted name in measuring equipment and this is our favorite tool. The 445713 hygro-thermometer is a handy all-in-one solution that shows you indoor and outdoor temperature and humidity. It has a max/min function so you can view differences over the period that passed since you last actively measured. It’s accurate down to +/-1.8 degrees F and +/-5% humidity.
Hang the 445713 on a nail or stand it up inside or outside your grow tent. Stick the probe into the soil in the shade under your plants. The display is big and clear for easy viewing even in low light.
8″ Copper Finish Decorative Indoor / Outdoor Thermometer
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If you’re old school, you may appreciate this simple and elegant wall thermometer from Bjerg Instruments. While it only shows you the temperature, you can hang it on the interior wall of your grow tent for a classy look.
If you’re only growing a few plants in a closet, this may be all you need. Plus, it’s just half the price of the Extech hygro-thermometer. But then you’ll still need a way to measure the humidity. Those little soil moisture meters won’t cut it.
AcuRite 00611 Indoor Outdoor Thermometer with Wireless Temperature Sensor & Hygrometer
- Digital thermometer | Monitor indoor & outdoor temperature, directly from the room thermometer
- Hygrometer | Humidity gauge allows you to track comfort levels inside & outside your home
- Wireless | Humidity and Temperature Sensor is weather resistant and can be placed indoor or outdoor
- Accurate | Wireless thermometer comes pre-calibrated for precise temperature and humidity readings
- Easy to Read | Large thermometer screen allows you to check weather conditions at a glance
Monitor conditions in your home environment. By tracking indoor and outdoor temperature and humidity conditions, you gain the information you need to take action and keep your plants healthy.
Now that we’ve covered some of the basic tools to measure environmental conditions in a grow room, let’s move on to what temperature and humidity levels are best for cannabis.
Heat your tent – Grow room heaters
Here’s a great little space heater for those cold grow rooms:
Portable Ceramic Space Heater 1500W/750W, 2 in 1 Oscillating Electric Room Heater
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- Easy control heater: Adjust the knob on the right to turn the unit on. “I” is for producing heat at 750 watts, “II” will produce heat faster and hotter at 1500 watts, and ”Fan” will blow out cool air. Then turn the thermostat knob on the left toward the + sign. The adjustable temperature range is 0℉ to 158℉. It will get the heater to cycle on and off according to if the room’s temperature reaching heater’s setting temperature
- Energy-efficient heater: Added 70 degrees oscillating switch on the top, PTC ceramic heating tech, and high-speed fan helps heat the room quicker and covers the space much more effectively. The heater put out tons of heat to heat up 200 square feet in seconds. Helps to save electric bills by heating up needed small spaces instead of heating the whole house with other centralized heaters. It’s quiet enough to use in a bedroom while sleeping
RIOGOO 9.5″x20.5″ Seedling Heat Mat and Thermostat Controller 68-108°F
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This heat mat and thermostat controller combo set increases the heat of soil moderately and provides optimum soil temperature for plants, so you have more confidence when waiting for your seeds to germinate.
Okay, besides making a grow tent warmer, how can you cool it down?
Cool your tent – Grow room fans and cooling
Let’s say you live in a tropical place where “cold weather” means you hit 65 degrees F at night. In that case, we hope you have an air conditioner. If not, get one for your weed. Or at the very least, try one of these solutions.
LG LW6017R 6,000 BTU 115V Window Air Conditioner, White
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Be prepared to take on the heat with the LG 6, 000 BTU 115V window air conditioner. Ideal for cooling a room up to 260 square feet coveted features include 3 cooling speeds, 3 fan speeds, 24-hour on/off timer, and an energy saver function.
Honeywell TurboForce Air Circulator Fan
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If you don’t have a ventilation system in place and you’re facing high temps in your grow room, try using fans to circulate the air. This quiet little fan from Honeywell has three speeds and can be hung on a wall.
Raise humidity – Grow tent humidifiers
If you happen to live in the desert, raising weed can be a challenge simply because your average daily humidity might be too low. Weed wants around 65% as a seedling, and at least 30% when you’re ready to harvest. This is hard when places like Phoenix and Las Vegas drop down to 20%.
Of course, you can spritz your plants with water to help raise moisture levels, at least temporarily. Or you can place an open container or two of water around the tent. This may not be enough either. If you live in a dry place, invest in a humidifier. You can run it on a timer so it can work while you’re playing.
Keep in mind that there are two kinds—cool mist and warm mist–and both may influence the temperature in the grow tent.
Raydrop Cool Mist 2.2L Humidifier
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- 2.2L (0.58GALLON) WATER TANK: The water tank offers up to 30 hrs of relaxing time on the lowest setting and up to 10 hrs working time on the high setting.
- MULTIPLE MIST SETTINGS: Adjust the mist output by rotating the dial knob, so convenient and precise.
- EASY TO CLEAN: Designed with 3.74 inches (9.5cm) large opening, raydrop humidifiers for the bedroom is really convenient for your daily clean and easy to refill.
- QUIET OPERATION: The new model of raydrop humidifier lowers the noise level to 30dB for quiet humidification without disturbing your study, working, or sleeping, away from those nasty noises.
- AUTO SHUT-OFF: raydrop humidifier will automatically shut off with red light on when runs out of water. Don’t worry about dry running when you are sleeping, since its auto-off feature will provide better protection for you.
Vicks VWM845 Warm Mist Humidifier
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This humidifier quietly releases warm, soothing vapor to help provide temporary relief from cough & congestion & help reduce respiratory discomfort so you can breathe & sleep better.
Lower humidity – Grow room dehumidifiers
Let’s imagine that you live in a humid place, maybe that town where those vampires and werewolves and that pasty-faced girl lived. Wait, you didn’t see the movie? That’s cool. Just think of a place where it rains a lot. Growing pot in high humidity means you’ll have to constantly watch for mold and mildew and growth problems. While seedlings like it wet, adult plants thrive around 40% humidity as they near harvest.
If you want to lower humidity in your grow tent and you live in a hot place, an air conditioner will help you a lot. If you don’t have one, you’ll need to upgrade your ventilation system or invest in a dehumidifier. Just blowing around with a fan won’t cut it.
Ivation Thermo-Electric Dehumidifier
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This Ivation Dehumidifier works silently. It takes care of small rooms by condensing water from the air and draining it into the transparent cup at the bottom. When the cup is full, it shuts down until you empty it. This is a low-cost solution for a small grow tent. In fact, be sure to monitor humidity levels to make sure this isn’t taking too much out of the air.
MIDEA MAD35C1ZWS Dehumidifier
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Able to collect 35 pints (50 pints 2012 DOE standard) of water a day and adjust humidity from 35% to 85%. Perfect for use in the basement, bathroom, bedroom, or crawlspace.
DampRid Hi-Capacity Moisture Absorber, 4-Pound Tub
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If you have a very small tent, DampRid is probably the cheapest way to control humidity. Again, just keep an eye on your hygro-thermometer.
Carbon dioxide, the greenhouse gas
Did you know that CO2 also affects the growth of your cannabis? If you have a large grow operation, you’ll want to invest in monitoring equipment for this factor too.
With a small home grow, all you need to worry about is getting fresh air to your plants. A simple fan will mix up the air and help the plants get the CO2 they need.
You may be thinking that all this is a lot to manage by yourself. Sure, you can put some things on timers, but it’s still a lot of monitoring and tweaking. Isn’t there an easier way? Of course!
The best controllers for temperature + humidity
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Make it easy on yourself. If you have a hydroponic setup, these controllers make grow tent or grow room climate control so much easier. They help with cannabis planted in soil too. You can monitor and control temperatures, humidity, CO2, and even control lights and watering with some of these babies.
Titan Controls Hyperion 1 Wireless Environmental Controller
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Titan Controls Hyperion 1 is the ultimate controller. You can mount the panel up to 150 feet away from your grow tent and still see what’s going on. It keeps track of temperature, humidity, and CO2 levels. If you add on a lighting controller, you can also take care of your grow lamps.
If temps get too high, Hyperion will save the day.
If the Hyperion 1 seems a little too much for your small setup, check out this controller below.
AutoPilot APE4100 Eclipse F60 Digital Environmental Controller
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- 4 outlets control temperature (heating & cooling), humidity and a cycle timed device
- Operates temperature and humidity outlets independently or synchronized
- Separate day/night temperature and humidity setpoints
- Cycle timer outlet modes: day only/night only/24 hours
- Cycle timer is programmable down to 1 second
Titan Controls 702450 Spartan Series Complete Digital Environmental Controller
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This controller will allow you to precisely monitor and control the environment in your grow room. Featuring an easy-to-use analog interface, this digital controller is easy to program and use. Each set point (temperature, humidity, and CO2) are programmed using a set of dedicated knobs. Readings are displayed on easy-to-read digital displays. The sensor which measures the temperature, humidity, light, and CO2 levels in your room attaches to the controller with a 15 ft cord. Enclosure resists dust, rust, and moisture. 14.5 Amps maximum/120 Volts/60Hz.
Other tools to help you grow the best cannabis
You’ll need a timer because even rocket scientists forget to turn off the lights sometimes.
Intermatic Two-Outlet Digital Indoor Timer
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This digital timer from Intermatic has two outlets so you can program different times for two devices, like lights and a fan, or a heater and humidifier.
Choose the best setup for your grow
Whether you have one plant or ten, design your grow setup ahead of time for the best results. Buy higher capacity or better quality products than you think you’ll need so you won’t have to replace them soon.
Save money by using LED lights instead of HIDs. It’s a bigger initial investment but you won’t spend as much on electricity and you won’t have to replace bulbs for up to ten years down the road. Plus, you won’t have to cool down your grow tent just because of the lights.
If you’re in doubt as to how much weed is legal in your area, check out this handy site that keeps track of the laws in various states. It’s always better to know before you grow. Then you can plan the appropriate precautions, like a good ventilation system with an odor-reducing carbon filter.
Once your plants have matured, use a bud trimmer to make harvesting easier and faster. And don’t toss out those leaves because you can use them to make cannabis oil.
Wrapping Up with MaryJane Farmer
We hope you enjoyed our guide to the best temperature and humidity controllers for growing cannabis. Learn more with our free guide to growing weed. Send me a photo of your grow operation: MaryJane@420beginner.com
Check back soon for more reviews of the best products to help you harvest the best buds or sign up for our growers’ newsletter.
Last update on 2025-01-13 / Affiliate links / Images from Amazon Product Advertising API
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