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. 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.
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
- 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
- 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.
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:
OPOLAR Oscillating Bathroom Heater
- 💖No longer feel cold in winter mornings💖 with this heater, your bathroom will be heated very quickly and you don’t have to rush into a robe. Please keep water away from the heater as the protection rating is IP21.
- 💖Get warm instantly💖 The heater will heat within 3s because of the ceramic heating elements. Besides, three settings are provided: Fan / 750w / 1500w.
- 💖Highly concerned your safety💖It will auto switch off when over heat and accidental be knocked off. The ALCI plug will protect the device if there is any electric shock.
- 💖Wide Heat Coverage💖The heater oscillates up to 80 degrees to fast heat your bathroom, home, office. The adjustable thermostat can maintain your room temperature to a certain degree.
- 💖Adjustable Thermostat💖This is a high tech home device that has a thermostat detector to maintain the room temperatures. No bother you to turn it off when feeling too hot.Super heat provider for your home, office and bathroom.
We like this little Opolar heater because it oscillates up to 80 degrees to fast heat your bathroom, home, office. The adjustable thermostat can maintain your room temperature to a certain degree. plus it’s made for the bathroom so it tolerates humidity well. 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.
RIOGOO 9.5″x20.5″ Seedling Heat Mat and Thermostat Controller 68-108°F
- Super Cost-Effective: Package includes 1-pack 9.5"*20.5" seedling heat mat and 1-pack digital thermostat controller Combo Set, very cost-effective and useful.You do not need to waste time to choose sepate seedling heat mat and Digital Thermostat Controller.
- Control the Temperature: Our digital thermostat controller is compatible with almost all seedling heat mats. The thermostat sensor probe delivers accurate readings in both cold and warm environments. Keeps a stable temperature between 68°F /20°C - 108°F/ 42°C for the professional needs.
- Keep Your Seed Root Warm: Our newly seedling heat mat will automatically warms rooting area 10-20F over unique temperature. For example, it can be used indoor or in a greenhouse, providing enough heat to keep your plant energetic and healthy.
- Super Easy to Use: Please put the heat mat on a flat and dry surface under a seedling tray and plug the cord into a standard 120V outlet to begin heating your roots. The digital controller has 3-button interface for simple operation and easy calibration.
- 1 Year Warrantee: We provide 1 Year Warrantee for our products.If any problem, we can resend a new one for you
This heat mat and thermostat controller combo set increases the heat of soil moderately and provide 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
- LOW NOISE PERFORMANCE: Operates at sound levels as low as 52dB (in low mode) eliminating unnecessary noise.
- MULTIPLE FAN SPEEDS: 3 cooling and fan speeds allow you to customize your cooling.
- MAXIMUM USABILITY: Easy to use electronic controls with remote
- AUTO RESTART: After a power failure, auto restart will automatically turn the unit back on when power is restored
- COOLS ROOMS UP TO 250 Square Feet: LW6017R is ideal for cooling medium rooms (10' X 25')
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
- 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.
- 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.
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.
Sunbeam Cool Mist Humidifier, White
- Brand New in box. The product ships with all relevant accessories
Improve indoor air quality in any room with the Sunbeam 1 Gal Cool Mist Humidifier. This powerful, easily portable device helps protect you from the effects of damaging, dry air.
Vicks VWM845 Warm Mist Humidifier
- RELIEF & COMFORT: 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.
- SPECIAL FEATURES: This humidifier's scent pad door allows you to enjoy aromatic Vicks VapoPads for added comfort & the Medicine Cup accepts inhalants like Vicks VapoSteam for cough relief
- COUGH & CONGESTION RELIEF: When you or your child has a cold, it can be difficult to sleep through the night. Humidifiers provide temporary relief so your rest won't be as disturbed by coughing fits.
- VICKS VAPORIZERS, HUMIDIFIERS, & STEAM INHALERS: Steam & humidity offer relief from cough & congestion due to colds or allergies, helping you breathe easier wherever you are, from bedroom to office
- TRY IT & SEE: Our humidifiers & vaporizers help you breathe better wherever you are.
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 around with a fan won’t cut it.
Ivation Thermo-Electric Dehumidifier
- 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.
MIDEA MAD35C1ZWS Dehumidifier
- 3,000 SQ FT DEHUMIDIFIER – Our dehumidifier are able to collect 35 pint (50 pint 2012 DOE standard) of water a day and adjust humidity from 35% to 85%, perfect for use in basement, bathroom, bedroom, or crawlspace. Maintaining a healthy 45%-55% humidity range has never been easier! Please note: depending on the climate in your area, as well as room size, you may need to purchase a larger unit for best effect
- INNOVATIVE FEATURES – Auto restart function limits disruption due to power outages by engaging your chosen settings as soon as power is restored. The auto defrost function prevents the collected water from being frozen and doing harm to the machine
- QUIET AND CONTINUOUS OPERATION – A maximum 51 decibel limit enables low volume operation equivalent to a quiet conversation. Meanwhile, with Energy Star certification, the unit features a continuous dehumidification mode designed to keep your home at the proper humidity level 24/7
- EASY MAINTENANCE – Easily empty the included tank (1.6 gallon) when it’s full, or simply connect a standard .75 inch female garden hose (not included) to the built in socket for gravity fed continuous draining. Meanwhile, a reusable filter preserves air quality without expensive replacement parts
- WORLDWIDE WARRANTY - Midea is the world’s largest provider of air conditioning products. As a testament to our dedication to quality, we offer a one year parts and labor warranty on this product
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 basement, bathroom, bedroom, or crawlspace.
DampRid Hi-Capacity Moisture Absorber, 4-Pound Tub
- DampRid Hi-Capacity Moisture Absorber Bucket attracts and traps excess moisture, eliminating musty odors from damp areas.
- The hi-capacity design features a unique Moisture Lock spill resistor technology with a sealed safety cover for a mess free solution.
- Ideal for larger spaces like basements, garages, where stagnant air and excess moisture is a problem.
- The 4 lb. Hi-Capacity bucket lasts up to 6 months, depending on temperature and humidity levels.
- To use, remove the plastic lid exposing the sealed safety cover. Discard once the moisture absorbing crystals have fully dissolved.
- 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
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
- 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
No products found.
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
- Country Of Origin: China
- Model Number: 702850
- Item Package Dimension: 12.2" L x 8.8" W x 6.4" H
- Item Package Weight: 4.6 lb
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
- 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 2021-07-27 / Affiliate links / Images from Amazon Product Advertising API
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