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Why and How to Control Temperature and Humidity in Your Grow Room

[UPDATED Nov 2019] Welcome to this roundup of the Best Temperature & Humidity Controllers to monitor your grow room and make sure you are growing the best cannabis.

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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).

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.

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. Like 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.

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 Humidity and Temperature Tools

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 hygro-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

Extech 445713 Big Digit Indoor/Outdoor Hygro-Thermometer
51 Reviews
Extech 445713 Big Digit Indoor/Outdoor Hygro-Thermometer
  • Simultaneous display of Indoor/Outdoor Temperature and Humidity
  • ax/Min with "reset" function
  • Humidity: 10 to 99% RH
  • Temperature: 14 to 140°F (-10 to 60°C)
  • Accuracy: ±5%RH; ±1.8°F, ±1°C

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

Bjerg Instruments 8' Antique Copper Finish Decorative Indoor/Outdoor Thermometer and Hygrometer
397 Reviews
Bjerg Instruments 8" Antique Copper Finish Decorative Indoor/Outdoor Thermometer and Hygrometer
  • 8 inch diameter indoor and outdoor wall thermometer and hygrometer (humidity measurement).
  • Easy to read 5.5 inch diameter dial face. Hygrometer gauge / humidity monitor at the bottom.
  • Simultaneous Celsius and Fahrenheit temperature display. Adjustable.
  • Steel construction with antique copper finish suitable to hang inside or outside your house or home.
  • Real glass lens on this wall mount indoor outdoor thermometer.

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.

Ambient Weather 8-Channel Wireless Thermo-Hygrometer

43%
Ambient Weather WS-07-C Big Digit 8-Channel Wireless Thermo-Hygrometer Display Console
531 Reviews
Ambient Weather WS-07-C Big Digit 8-Channel Wireless Thermo-Hygrometer Display Console
  • The WS-07-C is a big digit thermo-hygrometer display console. It can be used as a standalone display, or additional console for the WS-07 wireless system (add as many display consoles as you like to your existing system).
  • Simple to read, simple to use, and affordable, the WS-07-C includes an indoor thermo-hygrometer in the console and can remotely read and update up to eight remote thermo-hygrometer sensors at the same from the large digit, uncluttered jumbo display.
  • Eight additional wireless remote sensors can be added (F007TH) for comprehensive monitoring (not included).
  • The uncluttered display console displays temperature and humidity with jumbo 1.25" LCD characters which can be easily read from across the room.
  • Optional temperature and humidity calibration is provided for the upmost accuracy.

Our last selection is less expensive than the Extech but still a full-fledged hygro-thermometer. The Ambient Weather WS-07 doesn’t have a probe to check the soil but at least it can help you see how the air in your grow tent is doing.

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:

Holmes Digital Bathroom Heater Fan

Holmes Digital Bathroom Heater Fan with Pre-Heat Timer and Max Heat Output, HFH436WGL-UM
1,994 Reviews
Holmes Digital Bathroom Heater Fan with Pre-Heat Timer and Max Heat Output, HFH436WGL-UM
  • Holmes, wall mountable bathroom heater, blows warm air for quick distribution
  • Manufactured in China
  • Easy to adjust digital controls will help maintain your desired comfort level
  • Use the timer to pre-heat the bathroom and keep it warm and cozy
  • Bathroom safe ALCI plug for worry free bathroom use; and wall mountable
  • Digital thermostat with a digital clock and timer
  • 1 heat setting, 1500 watt max output. 1 Year Limited Warranty
  • The dB level is max. 60dB measured 1.5m distance from the heater.
  • Easy to adjust digital controls will help maintain your desired comfort level
  • Use the timer to pre-heat the bathroom and keep it warm and cozy
  • Bathroom safe ALCI plug for worry free bathroom use; and wall mountable
  • Digital thermostat with a digital clock and timer

We like this little Holmes heater because it has a built-in thermostat and timer, it hangs on a wall, plus it’s made for the bathroom so it tolerates humidity well. It’s cheap so it only has one setting, which is full blast. Just don’t point it directly at the plants.

Another way to raise the temperature for your plants is a heating mat. It’s like an electric blanket for your weed.

Apollo Horticulture 10″x20″ Seedling Heat Mat

Apollo Horticulture 9”x20” Seedling Heating Mat for Propagation and Cloning
556 Reviews
Apollo Horticulture 9”x20” Seedling Heating Mat for Propagation and Cloning
  • Package Includes: 1 - Apollo Horticulture Seedling Heating Mat
  • Dimensions: 9"x20" / Power Cord: 6'
  • Boost plant growth with the Apollo Horticulture Seedling Heat Mat: warms root area 10 to 20ºF above room temperature to improve root growth and increase germination rate.
  • Heavy duty: made of durable waterproof material to ensure a safe grow environment. Constructed using reliable materials held together by enhanced internal wiring. You can always rest assured that you are backed by quality hydroponics equipment from Apollo Horticulture.
  • Designed for indoor gardening: enhances seed germination process and increases success of seedlings and cuttings.

This heating mat from Apollo Horticulture will raise the temperature 10 to 20 degrees F to help your seedlings grow strong roots. It’s waterproof, an essential thing for using with plants.

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.

Frigidaire Mini-Compact Air Conditioner with Remote Control

Frigidaire FFRE0533Q1 5,000 BTU 115V Window-Mounted Mini-Compact Air Conditioner with Full-Function Remote Control
329 Reviews
Frigidaire FFRE0533Q1 5,000 BTU 115V Window-Mounted Mini-Compact Air Conditioner with Full-Function Remote Control
  • 5,000 BTU mini-compact air conditioner for window-mounted installation
  • Uses standard 115V electrical outlet, Product Dimensions - 15.2(W) x 16(D) x 12(H) inches
  • Quickly cools a room up to 150 sq. ft.
  • Dehumidification up to 1.1 pints per hour
  • Ready-select electronic controls allow you to easily select options with the touch of a button

Made to run off ordinary household current, this A/C window unit from Frigidaire cools and dehumidifies air in a room up to 150 square feet in size. You can wash the air filter to keep smells and bacteria under control. Plus, you can direct the air flow so it doesn’t blow directly on your plants.

Honeywell TurboForce Air Circulator Fan

39%
Honeywell HT-908 Turbo Force Room Air Circulator, 10 inch, Black
3,727 Reviews
Honeywell HT-908 Turbo Force Room Air Circulator, 10 inch, Black
  • FAN FOR TABLE OR FLOOR: The Honeywell Turbo Force Air Circulator Fan has 3 speeds & a 90 degree pivoting head; This quiet fan is compact and perfect for placement on the floor, but powerful enough to provide comfortable cooling in small to medium rooms
  • FEEL THE POWER: Honeywell's TurboForce line of fans have an aerodynamic turbo design to maximize air movement, offering the power for intense cooling or energy saving air circulation; The ease of a medium fan with power you can feel from 32 feet away
  • INCREASE YOUR COMFORT: Using fans for air circulation in your home can help increase your comfort, and help reduce energy costs as well; Honeywell carries a range of tower fans, floor fans, and oscillating fans find one for every room in the house;Fan diameter 12 inch
  • HONEYWELL FANS: The right fan helps cool you off & improves airflow in your room or home; Give your air conditioner & wallet a break by using fans to help reduce your energy consumption & costs; Honeywell carries a variety of fans to meet your home needs
  • HONEYWELL QUALITY: Help improve air circulation & energy savings in your home, bedroom or office with Honeywell fans; Compare to tower fans, oscillating fans, desk fans & similar fans Dyson, Blizzard, Turbo, Holmes, Vornado, and Pelonis

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.

Holmes Cool Mist Comfort Humidifier with Digital Control

17%
Holmes Cool Mist Comfort Humidifier with Digital Control Panel, HM1865-NU
271 Reviews
Holmes Cool Mist Comfort Humidifier with Digital Control Panel, HM1865-NU
  • Humidistat with ICD Display
  • Featuring 3 speeds and 16 hour programmable on/off timer
  • Filter treated with antimicrobial protection
  • 1.5 gallon tank capacity is ideal for larger rooms
  • Uses HWF65 C replacement filter

Sometimes we wonder if the folks at Holmes raise marijuana on the side because they make a lot of useful products for growing. Their Cool Mist Comfort Humidifier runs up to 48 hours on a single tank so you have to fill it fewer times. It has four settings so you don’t drown your plants in moisture. It will shut off when it reaches the desired humidity, and it also has a timer.

Holmes Warm Mist Humidifier

While not as fancy as their Cool Mist Humidifier, the Warm Mist Humidifier from Holmes runs up to 24 hours on a single tank.

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 around with a fan won’t cut it.

Ivation Thermo-Electric Dehumidifier

Ivation 13-Pint Small-Area Desiccant Dehumidifier Compact and Quiet - With Continuous Drain Hose for Smaller Spaces, Bathroom, Attic, Crawlspace and Closets - For Spaces Up To 270 Sq Ft, White
111 Reviews
Ivation 13-Pint Small-Area Desiccant Dehumidifier Compact and Quiet - With Continuous Drain Hose for Smaller Spaces, Bathroom, Attic, Crawlspace and Closets - For Spaces Up To 270 Sq Ft, White
  • 13-PINT DESICCANT DEHUMIDIFIER – Highly Efficient Desiccant Rotor Removes Moisture, Odors & Mold While Warming Ambient Air; Perfect for Colder Seasons
  • LIGHTWEIGHT BUT POWERFUL – Enjoy Adjustable Humidity Control & Whisper Quiet Operation for Small Spaces Up to 270 Sq/Ft in Home, RV, Boat or Laundry Room
  • USER-FRIENDLY LCD DISPLAY – Sleek Digital Interface Lets You Power On/Off & Adjust Humidity, Fan Speed, Timer/Sleep Mode, Vent Swing & Screen Brightness
  • MULTIPLE DRAINAGE OPTIONS – High Capacity Reservoir Holds Up to ½ Gallon of Water for True Portability; Includes Connection Hose for Continuous Drainage
  • VERSATILE PERFORMANCE – Works in Temperatures from 33°F to 104°F; Convenient Carry Handle, Washable Filter, Alerts, Auto-Shutoff & Adjustable Swinging Air Vent

This Ivation Dehumidifier works silently. It takes care of small rooms by condensing water from the air and draining 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.

Frigidaire 50-pint Dehumidifier

24%
Frigidaire FAD504DWD 50-pint Dehumidifier
12,630 Reviews
Frigidaire FAD504DWD 50-pint Dehumidifier
  • 50 pints per day dehumidifier for a room up to 1000 sq. ft.
  • Protects your home from mold and mildew caused by excess moisture
  • Front, pull-out 16. 3-pint tank with handle and splash guard
  • Electronic controls with digital humidity readout and 2 fan speeds
  • Helps eliminate bacteria in the air that can make breathing difficult

This beast from Frigidaire can run continuously if you run a hose to a drain. If you have a large grow setup in a damp basement, this is the dehumidifier of your dreams.

DampRid Hi-Capacity Moisture Absorber, 4-Pound Tub

11%
DampRid FBA FG50T Hi-Capacity Moisture Absorber, 4-Pound Tub, Fragrance Free, 4 Pound
1,152 Reviews
DampRid FBA FG50T Hi-Capacity Moisture Absorber, 4-Pound Tub, Fragrance Free, 4 Pound
  • The product is 64OZ Moisture Absorber
  • Easy to use
  • The product is manufactured in China
  • Protect large problem areas from moisture damage
  • Use in basements, crawlspaces, garages, storage rooms, vacation homes, boats & RV’s
  • Eliminate musty odors caused by excess moisture
  • Attract and trap excess moisture in your space
  • Spill resistant safety cover
  • Protect large problem areas from moisture damage
  • Use in basements, crawlspaces, garages, storage rooms, vacation homes, boats & RV’s
  • Eliminate musty odors caused by excess moisture
  • Attract and trap excess moisture in your space

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

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

Titan Controls Wireless Environmental & Lighting Controller, 120V - Hyperion 1
2 Reviews
Titan Controls Wireless Environmental & Lighting Controller, 120V - Hyperion 1
  • Complete control of your grow room from up to 150 feet away without wires
  • Monitor & control the CO2, temperature and humidity during the day & night periods
  • Add a fully functional lighting controller (via trigger cordsets)
  • Even tells you when to change your grow bulb
  • 15 Amps maximum/120 Volts/60 Hz

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 Digital Combination Recycling & Lighting Timer

Autopilot Master Digital Timer
6 Reviews
Autopilot Master Digital Timer
  • Autopilot Master Digital Timer
  • White

The Autopilot Master Digital Combination Recycling and Lighting Timer is made by hydroponics specialist company Hydrofarm. It can manage your lights as well as a CO2 injection setup. It protects your weed from too-high temps, too.

Titan Controls Digital Day and Night Controller with Photocell

17%
Titan Controls Digital Environmental Controller w/ Photocell, 120V - Saturn 4
8 Reviews
Titan Controls Digital Environmental Controller w/ Photocell, 120V - Saturn 4
  • The Saturn 4 is a basic environmental controller
  • It's digitally precise with easy to use knob's to dial in your desired temperature and humidity settings
  • Will operate a CO2 controller, fan, dehumidifier and a night only device to keep your garden flourishing

The Saturn 4, also from Titan Controls, is an analog grow room environmental control system that manages a fan, dehumidifier, a CO2 device, and another device that you only want to run at night. (The photocell is what it uses to determine when nighttime is for your plants.) It has a remote sensor on a 15-foot cable so you can plant it in the soil.

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

5%
Intermatic DT122K 15-Amp Two-Outlet Heavy Duty Digital Indoor Timer
262 Reviews
Intermatic DT122K 15-Amp Two-Outlet Heavy Duty Digital Indoor Timer
  • This heavy-duty indoor digital plug-in timer can be programmed with up to 7 on/off program settings for either daily (24 hour) or weekly (7 day) schedules
  • Provides two grounded outlets and controls LED and CFL lights and other 15 Amp loads
  • An optional random setting turns items on/off at times up to 15 minutes before or after the programmed time, allowing for a more 'lived in' look
  • The astronomic feature automatically adjusts to sunrise/sunset times throughout the year
  • This plug in outlet timer features an automatic Daylight Saving Time adjustment so you won't have to re-program your timer twice a year

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 to our growers’ newsletter.

Last update on 2019-11-13 / Affiliate links / Images from Amazon Product Advertising API

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