Cannabis Temperature Tutorial
Cannabis plants like a temperature similar to humans, or a little warmer – not too dry, not too humid.
For a lot of indoor growers, that is all you need to worry about. If it feels too hot or too cold for you in your grow area, it’s probably too hot or too cold for your cannabis plants as well.
Cannabis plants like about the same temperature as humans!
If your grow room feels warm or cold, humid or dry, that is a sign that you may want to look into changing the temperature or humidity of your grow area.
Generally, cannabis plants prefer temperatures in the 70-85 °F (20-30 °C) range during the day when lights are on. When grow lights are off (their “night”), cannabis plants are happy with slightly cooler temps.
Optimal Temps For Growing Cannabis
Vegetative Stage: Young growing cannabis plants in the vegetative stage like it a little warmer in the 70-85°F (20-30°C) range. More about temps in the vegetative stage.
Flowering Stage: In the flowering stage (when cannabis plants start making buds), it’s best to keep temps slightly cooler, around 65-80°F (18-26°C). This isn’t for the plants themselves as much as to ensure the best bud quality. Slightly cooler temperatures in the second half of the flowering stage helps produce the best bud color, trichome production, density, and smell. To really bring out colors, aim for a 10°F (8°C) difference between day and night. More about temps in the flowering stage.
Proper temperature brings out colors and can increase bud quality
7 Essential Concepts About Temperature Control
- Venting is your friend – Hot air should vent out of the grow space if heat is a problem. Vent air to the outdoors if you want to prevent the hot air from being recirculated around the grow room.
- Fans only push air around – It’s a common misconception that fans bring down the temperature, but fans don’t cool the air. They provide a breeze and help level out the temperature within an area. If it’s hot in your grow tent but cool in your room, then a fan will help equalize the temperatures. But if your entire room is too hot overall, then fans won’t bring the temperature down.
- ACs and Evaporative Coolers bring the temperature down – Besides exhausting your heat outdoors, the only way to bring the temperature down is to use an AC or Evaporative Cooler. Note: An AC will work in any climate, but evaporative coolers need dry air and only work when the humidity is under 30%.
- Strain makes a difference – Heat and cold bother certain plants more than others. The strain has a significant effect on a plant’s heat or cold resistance. Get a list of heat-resistant strains.
- Choose the right light schedule– Too hot during the day or too cold at night? Switch your timer’s on/off cycle, so your grow light is on at night and off in the day. Switching the time your grow lights are turned on will help equalize day and night temperatures. It may even reduce your electricity bill as some people get charged less for electricity used at night. Keeping grow lights off during the day will help with heat, while your grow lights being on at night will keep plants warmer when it’s the coldest.
- Get Extra Help – Here are 3 supplements that help cannabis with heat stress, and here are some tips for growers dealing with the cold.
Why Temperature Matters to YOU As a Grower
Why Is temperature critical when growing cannabis? Can cannabis stand freezing temps? What happens if your grow room gets too hot?
Different afflictions can happen from high or low temps, so let me break that down for you.
Learn more details below…
Too Low (Cold) Temps
Colder temps will tend to slow down growth. Temps lower than 60°F (15°C) tend to upset plant growth, and freezing temperatures will shock or even kill a cannabis plant. Some plants continue growing in the cold without signs of stress, but they often don’t yield as well as they should given the amount of light they receive.
Plants are also more susceptible to certain types of mold when it’s cool, especially if it’s damp, too. Mold sometimes occurs after frost melts and gets water all over your plants.
Colder temps and significant temperature fluctuations contribute to the over-purpling of leaves and can also reduce photosynthesis.
A plant that is grown in relatively cold temps can survive, but it will never grow as fast or as well as a plant living in a good environment. Indoor plants tend to be much more susceptible to cold than outdoor grown plants.
This plant is drooping after experiencing a cold night
Too High (Hot) Temps
While cannabis plants don’t usually die from the heat, too hot temps will cause plants to grow much more slowly.
Please note temps above 80°F (26°C) in the flowering stage will slow down bud growth and may cause them to become airy and loose. The heat can also reduce the potency and smell of your buds. Keeping the grow room temperature under control is especially important in the flowering/budding stage!
In the heat, cannabis is also more susceptible to many problems, including spider mites, white powdery mildew (especially if it gets humid, too), root rot, nutrient burn (from increased water transpiration), increased stretching, wilting due to root oxygen deprivation, and reduced “smelliness” of buds (as terpenes can burn away at higher temps).
More About the Upper Limits of Temperature
With bright grow lights (such as LEDs or 600W HPS and brighter), cannabis plants of all stages can thrive at slightly higher temps up to a max of about 85°F (30°C) even with no CO2 enrichment, as long as there is low relative humidity and plenty of air movement.
Cannabis plants can thrive at even higher temperatures, up to an ultimate max of about 95°F (35°C), in an environment with low humidity, extremely bright grow lights, and enriched CO2 (above 1500 PPM) – this is not your average grow! Learn more about CO2 here: https://www.growweedeasy.com/co2-marijuana-yields
Temperature & Humidity Adjustment Cheat Sheet
- Dehumidifier– Raises Temperature (somewhat), Lowers Humidity
- Space Heater– Raises Temperature, Lowers Humidity
- Air Conditioner– Lowers Temperature, Lowers Humidity
- Evaporative Cooler– Lowers Temperature, Raises Humidity
- Humidifier– Raises Temperature (somewhat), Raises Humidity
What else is affected by the temperature in the grow room?
Bud Color – The temperature experienced by your plants influences the color of buds and leaves. The temperature either suppresses or brings out blues, purples, and pinks if your strain has the genetics for it. Learn how to grow pink or purple buds.
Plant Growth Patterns – Temperature fluctuations can actually change how your plant grows! Warmer night temperatures tend to slow down upward growth. Cannabis generally prefers a cooler temperature at night. Maintaining slightly lower temps during the dark period will encourage your plant to grow as fast as possible.
Relative Humidity – Temperature has a significant effect on the relative humidity of your grow area.
Drying & Curing – Temperature is incredibly vital to the drying & curing process. A professional dry/cure is one of the most significant factors when it comes to producing top-shelf buds.
Cool night air can trigger purpling in some plants
Tip: Use Temperature to Help Control Growth!
Cannabis generally prefers slightly cooler temperature at night, and warmer night temperatures will tend to slow down upward growth. But… you can occasionally use this knowledge to your advantage to help control plant growth!
By artificially raising temperatures during the dark period, it will slow stretching plants that are growing too tall too quickly. That means warmer nights can be a helpful way to reduce the “stretch” if you’re growing in a situation where you don’t have a lot of vertical room. And never forget about supercropping, the ultimate way to break down the height of your plant at any time.
By keeping temps a bit cooler during the dark period, you will encourage your plants to grow as fast as possible.
Temperature & Humidity (VPD)
In this section, you will learn a little bit more about how the temperature in your grow room affects the humidity.
Before we talk about VPD, here are some humidity guidelines for growing cannabis
Although those are general guidelines, plants can thrive at different relative humidities depending on the temperature of the air.
Once the air becomes too saturated with water, it tends to form dew or films of water over leaves, which leads to mildew and bud rot. Plants also tend to grow more slowly in very high humidity.
Wet or humid conditions can lead to bud rot
Temperature and relative humidity (RH) are closely related to each other. Sometimes you can overcome a problem with one by fixing the other.
“Humidity” measures how much water is currently “being held” in the air. “Relative humidity” compares that amount to the maximum amount of water that air holds at that temperature.
For example, Warm air can “hold” more evaporated water than cool air
For those interested in learning more about the science behind this, there is a term used by greenhouse growers known as VPD or “Vapour Pressure Deficit,” which roughly measures the temperature and relative humidity.
According to Wikipedia: “the ideal range for VPD in a greenhouse is from 0.45 kPa to 1.25 kPa, ideally sitting at around 0.85 kPa. As a general rule, most plants grow well at VPDs of between 0.8 to 0.95 kPa.”
When growing cannabis plants, relative humidity (RH) is just as important as the temperature of the air and is something you should pay attention to, especially if you notice that your grow room is dry or humid.
If your grow area is particularly dry or humid, you should pay attention to RH (Relative Humidity) in the grow room…
You need to control both temperature and RH at the same time to get the best results when growing cannabis.
If the air is too hot and dry (high VPD), plants will tend to have slow, stretched growth.
If the air is too cool and humid (low VPD), plants grow slowly and are prone to problems with mold or fungus.
Note: Pay attention to buds. The best VPD for water moving through the plant does not necessarily match the best temperature/humidity for bud growth, smell, and development. Additionally, each plant is different. As growers, we care more about bud quality than VPD, so make sure to pay attention to your plants before VPD numbers.
Clones prefer higher humidity than plants with developed roots
Optimal Temperature At Different Life Stages
Preference: Comfortable Room Temperature or Slightly Warmer 70-85°F (20-30°C) – High humidity preferred (60-80%)
Clones do not have a root system yet, and so they need to get all their water via transpiration of the leaves until their roots form. Therefore, clones prefer humid conditions with plenty of water evaporated in the air. That’s why many people use a humidity dome or “cloner” to artificially raise the humidity for clones. However, like anything in life, there can be too much of a good thing. You shouldn’t let the humidity get higher than 80% if possible because it can encourage the growth of mold or mildew, and may cause plants to root slower.
Clones seem to root and grow the fastest when the temperature is slightly warm, about 70-85°F (20-30°C), just like a cannabis plant in the vegetative stage.
Seedling & Vegetative Stage
Preference: Comfortable Room Temperature or Slightly Warmer 70-85°F (20-30°C) – Avoid very low humidity
Young seedlings tend to grow faster with mid-to-high humidity and warm temperatures.
However, a cannabis plant’s ability to withstand drier and colder/warmer conditions tends to increase as it gets older. Outdoor-grown plants tend to be much more robust about temperature fluctuations than indoor plants.
It’s good to aim for a temperature of 70-85°F (20-30°C), during the vegetative stage. It’s not always possible, but try to give plants slightly cooler temps during the dark period than during the light period as long as you stay within the recommended range.
Maintaining slightly cooler night temperatures (in the specified range) tends to promote the fastest and healthiest vegetative growing for cannabis plants.
Two happy vegetative plants getting a comfortable 75°F (24°C)
CO2 Enrichment Changes the Optimal Vegetative Temperature
Vegetative cannabis plants like higher temps when you supplement the grow room with CO2, but there are a few critical things you must know about CO2.
- Seal the environment and maintain at least 1500 PPM of CO2 in the air
- Provide a lot of light (more light than your plants would typically be able to use)
- Keep temperatures between 85°F (30°C) and 95°F (35°C).
- Avoid high temperatures after buds start forming, so they develop properly
Preference: Avoid hot temps! 65-80°F (18-26°C) – Mid-to-Low humidity – Slightly cooler at night than during the day
In general, you should strive to keep temps under 80°F (26°C) throughout the flowering stage, and especially towards the crucial second half when buds are in the midst of development.
The temperature in the flowering stage is too important to ignore. That’s because keeping temps low during the flowering stage will help your plants produce the most potent, dense, smelly, and trichome-covered buds as possible.
Unfortunately, higher temperatures during the flowering stage can cause plant problems and slowed bud growth. It can also cause terpenes and potency to evaporate into the air.
What that means is if your buds stay too hot during the flowering stage, the higher temperature may accidentally be burning away some of your terpenes and cannabinoids (reducing the final taste/smell/potency of your buds after harvest).
Read more about how to improve the taste and smell of your buds here: https://www.growweedeasy.com/better-taste-better-smell
It is especially important to make sure buds are not exposed to too-hot temps after week 6 or 7 of flowering, as this is when the terpene content in the buds starts to ramp up.
Give plants colder temperatures at night, especially towards the end of the flowering stage
Note: Slightly chilly is okay, but never expose your plants to freezing temps!
Too-cold air can cause buds to grow airy and loose
Bonus! In addition to improving taste and smell, terpenes can affect the color of plants and cannabis buds. For example, terpenoids are what gives tomatoes their red color. The same process may be at work with certain cannabis strains, too. By maintaining lower night temperatures in the last few weeks before your cannabis harvest, you will help bring out colors in your cannabis (purple, pink, blue, etc.). Of course, this only works if your strain has the genes to produce colored cannabis buds. Most strains will only grow green buds, but if your plant can produce other colors, cooler night temps can help bring them out!
Drying & Curing Buds
While starting with good genetics and properly caring for plants is key to growing top-shelf quality buds, your job isn’t over when you cut down your plants at harvest. I’d say that almost 50% of the final bud quality is determined after you cut down your plants, but how you choose to dry & cure your buds.
Buds that have been professionally dried and cured are more potent, denser, smoother to smoke, look better, and have that coveted “sticky-icky” feeling.
The main thing you must do as a grower to professionally dry and cure your buds is to maintain the proper temperature and humidity during the process. If you follow the right method, you never have to worry about mold or overdrying, and you will get beautifully cured buds every time.
Learn more about how to professionally dry & cure your buds here: https://www.growweedeasy.com/how-to-cure-buds
Choose Proper Grow Lights For Your Grow Area
Many cannabis growers worry about how their indoor grow lights will affect the temperature of their grow room. Heat production from grow lights is a valid concern, and this section will break everything down for you.
CFLs & Other Fluorescent Lighting
CFL grow lights can be purchased from the grocery store and can be kept mere inches from your plants, so they are great for growing in very short/tight spaces where ultimate stealth is the biggest goal.
CFL grow lights have earned a reputation for being very low heat. And, indeed, you can successfully grow a cannabis plant under just a few CFLs, and they won’t give off much heat.
However, if you want to get bigger yields, you’ll have to keep adding more and more CFLs, and the heat they give off will start building up.
I generally don’t recommend growing more than 1 or 2 cannabis plants at a time under CFLs – if you want to grow more plants than that, I highly recommend upgrading to a small HPS grow light instead.
Other fluorescent lighting uses very similar technology as CFLs, but the bulbs come in different shapes, some of which can be more suitable for growing. While not as stealthy or small as CFLs, other fluorescent lighting can be a cheap and effective way to nurture young cannabis plants.
HID Grow Lights – Metal Halide (MH), High Pressure Sodium (HPS) & LECs/CMH
MH/HPS/LEC grow lights are known for using a lot of electricity and producing a lot of heat. And while that’s true for the bigger models of HID lights, I think a lot of growers overestimate how much heat will be produced by the smaller HID models.
For example, a lot of people recommend that new growers get CFLs instead of HIDs so that there’s less heat in the grow room. Yet it’s essential to keep in mind that 250W of HPS light will produce about the same amount of heat as 250W of CFLs, except that you’ll get more light and better yields with HIDs. Another advantage of HIDs over smaller lights like CFLs is good models of HIDs come pre-built to accommodate cooling via an exhaust system.
That’s why it’s easier to cool an equivalent amount of HIDs compared to CFLs.
However, HIDs do need more height than growing with CFLs, so if the height is limited, than HIDs may not be the right choice for you.
But, if you do have the height to accommodate an MH/HPS light, I highly recommend going for that over CFL grow lights. In my opinion, CFL grow lights a best in very short/tight spaces where ultimate stealth is the biggest goal.
Learn About LEC/CMH grow lights (highly recommended as it seems to beat other HID lights for yields, smell, and trichome production)
LED Grow Lights
LEDs are known for needing just a little electricity and for producing less heat than HID grow lights like MH or HPS lights.
But is all the marketing hype true?
It’s actually a lot more complicated than just a “yes” or “no” answer. The truth is, some LED grow lights work incredible, and some are a ripoff. It’s helpful to educate yourself about LED grow lights to make sure you get exactly what you’re looking for.
How to Control Temperature in the Grow Room Step-By-Step
Step 1: Get a Way To Monitor Temperature (Thermometer)
In addition to measuring the temperature, it’s also important to know the relative humidity (RH) of your grow room. So you might as well get a thermometer that measures both temperature and humidity at the same time.
But it’s not necessarily that easy. The quest to find the perfect thermometer/humidity monitor can be tough.
While you can find cheap ones at the local store, you may notice that a lot of the cheaper models are a few degrees “off”. A few degrees probably won’t have a massive effect on your results, though. Some growers will buy 2 or 3 different thermometers and use the average to determine what’s really going on in the grow room. I have several that I’ve picked up over the years, and they all sit in my grow room now.
Here’s a popular thermometer/hygrometer that has all standard features and costs $12
That model works pretty well, but next is the temperature and humidity monitor that I use primarily. The humidity number is more prominent on the screen because it was initially made for incubating chicken eggs (humidity is critical to egg hatching rates). I’ve found that many thermometers slowly die from the heat of a grow light, but this particular one seems to keep on trucking despite the extreme environment. I bought my first one over 5 years ago, and it still works great.
This thermometer ($25) seems more accurate than many others I’ve tried and is resistant to heat from grow lights
It can be tough on the quest to find the perfect thermometer/humidity monitor, especially if you don’t want to spend a pretty penny. I like this one. It only costs $8, and it comes with a probe. I have the probe hanging in my grow tent near the plants, with the screen outside the tent. This setup makes it easy to see the temperature and humidity exactly where the plants are without having to open the tent.
I like that this thermometer/hygrometer ($8) has a probe you can hang in the grow space.
Step 2: Refer to Temperature Chart
Chart – optimal temperature for growing cannabis plants
Vegetative Stage: 70-85°F (20-30°C)
Flowering Stage: 65-80°F (18-26°C)
If your temperature is too high or low….
Step 3: Correct Too-High or Too-Low Temps (explained)
There are many tools available to help you control the temperature of your grow room.
Both hot and cold in your grow room? For those who struggle with both hot and cold temps where you live, you may want to consider getting an All-in-One Heater & Air Conditioner.
Too Hot: What to Do
Exhaust System: Make sure you have a sound exhaust system to pull out hot air and increase air circulation to your plants. If you don’t have an exhaust fan pulling hot air from your grow lights outside, fixing that is your first step. Remember! An exhaust system is important not only keeps temps down; it improves the air circulation your plants need to thrive. Learn how to set up a proper exhaust system here: https://www.growweedeasy.com/hps-grow-lights-setup
Tips for controlling the heat in the grow space using an exhaust system
Air Circulation: If there is a lack of proper air circulation in the grow room, you will tend to get hot spots that can damage your plants. It’s always a great idea to install fans in the grow room to help circulate the air inside the tent. Remember, don’t point fans directly at plants. Leaves can be rustling slightly, but stems should not be waving around due to the direct breeze of the fan. I like to point fans somewhat over or under the canopy, so it doesn’t aim directly at plants. Sometimes I point the fan at a wall to move the air around without blowing on the plants.
Change the Light Schedule: If you’re in a situation where the temperature is climbing too high at specific parts of the day, then you can change your light schedule so that your grow lights are off during the hottest part of the day. For example, in the vegetative stage, your plants need 18+ hours of light each day. If it gets too hot in the middle of the day, you could set your timer to turn your lights off for 6 hours during that part of the day. This strategy will not fix a major heat problem but can help alleviate symptoms of heat stress during a short hot spell or heatwave.
Consider Getting Different or Smaller Grow Lights: Learn about different grow setups.
AC or Evaporative Cooler: If you have good air exchange and have tried all the steps above, but the temperature in the grow area is still too hot, you will need to use a piece of equipment that can lower the temperature of the air.
Air Conditioner – (some are portable, some ACs fit in your window) – in addition to cooling the air, an AC will also tend to lower the relative humidity of the air. To be effective, and AC must be able to exhaust hot air outside the house, just like hot grow lights. If the air outside the grow tent is already too warm, you will need to get an AC to pre-cool the air before it enters the grow tent. No matter how strong your exhaust system, it won’t be able to bring the temperature lower than your ambient room temperature. If you need to lower the ambient room temperature, you’re going to need a way to cool the air, and air conditioners are hands-down the most effective way to cool your air.
Swamp cooler – (also known as an “evaporative cooler”) Ideal for those where it’s both hot & dry as the swamp cooler will bring down temps while also adding additional humidity to the air. Works best when humidity is too low, and the temperature is too high. Repeat: these do NOT work well if your humidity is above 30% RH! Read how one user used a swamp cooler to control his temps & humidity.
Too Cold: What To Do
If it’s too cold in your grow room, sometimes you have additional options besides just getting a heater, such as getting a stronger/hotter grow light or using extra insulation to contain the heat of the grow lights you do have.
If your plant is not insulated from the cold (for example, if it’s growing in the middle of your garage, basement, attic, etc.), then the first step is to make sure your plant is adequately insulated. It’s cheaper and easier to insulate a small space, so create a dedicated grow box or get a grow tent that will act as the outward bounds of your grow area.
Then you can buy rolls of insulating materials for cheap at your local home improvement store and use these to insulate your grow area further. Insulation will help keep the cold air out, and the hot air inside.
Reflectix material is both reflective and insulating. Line the inside of your grow space to help contain heat.
With a properly insulated grow box, your grow lights will likely provide enough heat to keep your cannabis plants warm unless you live in a freezing cold area, or perhaps if you’re in the middle of winter or a cold spell.
If you must get a heater to keep your plants warm, avoid letting it blow hot air directly on your plants, and especially avoid ever having it in the tent with your plants. You want a heater that radiates heat out evenly, instead of pushing out a blast of hot air like a space heater. Never allow hot air to blow directly on any part of the plant. Most heaters can turn on and off depending on the temperature, so they turn off when unneeded.
The following model of heater is an excellent example of the type of heater you want for your grow room – it puts out gentle heat and has a thermostat you can use to have it automatically turn on and off as needed. The heat radiates out instead of being pushed out (which you don’t want in your grow room). It’s almost entirely silent. Plus, it comes with a timer, so you can have it preset to turn on just before lights go off for the night (or whatever you need for your space).
This heater gently radiates heat instead of blow hot air
Keep roots warm and up off the cold floor
If you’re growing in a basement or garage, it’s common for the floor to be cold. If growing plants in containers, it can help to put them on a piece or some other barrier to prevent them from sitting directly on the floor.
Some people are growing in a garage or attic that is okay during the day but is getting too cold at night when their grow lights go off.
It can help to switch your timer’s on/off cycle, so your grow light is on at night and off in the day.
Switching the light schedules helps equalize day and night temperatures. Keeping grow lights on at night will keep plants warmer when it’s the coldest.
Change your timer so grow lights are on at night
However, to get most cannabis plants to start making buds, you need to give them at least 12 hours of complete darkness every night, which means grow lights need to be off for 12 hours/day. For some growers in a wintry climate, a 12-hour dark period (even during the day) will send the temperature plummeting too low.
But did you know there’s a type of cannabis that will make buds even if you leave your grow lights on for 24 hours a day?
Auto-flowering strains let you keep your grow lights on for 24 hours/day, which helps keep plants warm in cool growing areas!
They are described as “auto-flowering” because these strains will automatically start making buds and be ready to harvest in about 3 months, no matter what light schedule they get! This lets you leave your grow lights on all day, every day, so your plants stay warm!
An example of autoflowering plants
Be Prepared For When the Electricity Goes Out!
One challenge for growers in wintry climates is the impending chance of a power outage during the winter months. Indoor growers rely on electricity to keep plants alive, especially in the winter, so try to prepare ahead of time!
And while you’re here…
Strain Makes a Difference!
Some strains are much hardier than others when it comes to the cold. If possible, it helps to pick a cold-resistant strain. Learn where you can get seeds.
One advantage of cold temperatures is it tends to bring out colors like purple and pink
Too Hot for Pot?
Marijuana plants can grow and survive practically anywhere regardless of the climate, hence the nickname “weed.” However, they will struggle and likely not produce desirable effects if the temperature is too hot.
The easiest way to prevent heat problems is to select strains that do well in your particular climate. You can also use grow rooms or greenhouses to create ideal environments. However, even if you create a dedicated indoor space, you’ll still need to pay close attention to the temperature. You don’t want it to be too hot for your plants.
Whether you are growing outdoors in Las Vegas or setting up an indoor grow room in Detroit, you’ll need to watch your plants carefully for signs of heat stress. Even in a grow tent, if your marijuana grow tent temperature is too high, your plants will start to have problems.
About Too Hot for Pot?
Symptoms of Heat Stress
In general, a sign of heat stress in marijuana plants are curling leaves. Here are some other signs to look out for:
- Leaf edges that curl upwards
- Burnt leaves with the tips that appear brown
- Wilting and drooping of the entire plant
- The development of foxtails. This is where a plant grows a new bud on top of the initial one. Foxtailing often occurs during the flowering stage .
Too much heat can be a real problem. When marijuana plants are exposed to extremely high temperatures, they are susceptible to:
- spider mites
- root rot
- nutrient burn, which is as a result of increased water transpiration
- white powdery mildew, which is a result of too much humidity
- Wilting, which is a result of lack of enough oxygen
- Buds that lack smell. This because terpenes burn away at high temperatures
- Increased stretching
Do marijuana plants stop growing at certain temperatures?
The good news is marijuana plants do not stop developing when there is too much heat. However, their growth will slow down. This is because too much heat affects the process of photosynthesis. The activities of the enzymes are also stunted, and the plants produce very few proteins. However, if it is exposed to heat for long durations, your plant might end up dying.
If you are growing marijuana in a grow room, keep in mind, the maximum temperature for marijuana grow tent success is 85 °F. Temperatures higher than this will result in the plant’s death.
When the marijuana grow room temperature is above 85 degrees Fahrenheit, photosynthesis will be affected; however, the plant will still produce sugar. For the sugars to be distributed throughout the plant, the plant temperature should be above 20ºC or 60ºF. In the case of sugars, heat is a good thing. If the plant is not warm enough, the sugars will be stuck, and the plant will suffer. Once the plant is warm enough, the sugars will be distributed to their respective places.
However, if the temperature is above 85ºF during the flowering stage, bud growth will be stunted, which may result in an airy and loose bud. The potency and smell of your buds may also be reduced. Maintaining the right temperatures during the flowering stage is crucial if your goal is to produce densely packed buds.
How to grow marijuana in extremely high temperatures
In some areas, high temperatures cannot be avoided. In that case, you may want to consider using a grow tent. Grow tents help ensure an ideal marijuana grow room temperature . They do this by using an exhaust system to move hot air from the grow tent to the outside. If you are not using an exhaust system, you should, at least, make sure you have enough ventilation. An air conditioner can also remove hot air and cool an indoor growing area. Also, keep in mind that your lights will cause heat. Choosing low heat options will lower the temperature in your growing area.
Whether you use a grow tent or grow your plants indoors with an air conditioner, maintaining the ideal temperature is essential for producing the highest quality harvest.
What is the ideal temperature for growing marijuana?
Maintaining the ideal temperature for your marijuana plants when using a grow tent is not always the easiest thing to do. This is because marijuana plants require different temperatures at different stages of their growth.
During the vegetative stage, marijuana plants thrive in temperatures between 70-85 degrees Fahrenheit (20-30ºC). This is also the maximum temperature for marijuana grow tent use.
During the flowering stage, however, the ideal temperature to grow marijuana plants can be a little colder. The temperature should be kept between 65-80 degrees Fahrenheit (18-26ºC). The second half of the flowering stage is when the temperature should be at its coolest. This helps your marijuana plants produce flowers with rich color, as well as increased trichomes, denser buds, and more potent smell.
When growing outdoors, the ideal temperature is a little cooler. Marijuana outdoor grow temperature is best when it is close to 60ºF.
On the other hand, you also don’t want it to get too cold. When using a tent, the marijuana grow tent temperature should always be above 60ºF. Anything below that and the plant growth will be stunted, the plant may freeze, and it will eventually die. Sometimes you might experience a night or two where temperatures may fall below 50ºF, but as long as it is not prolonged, you don’t need to worry. Keep in mind, outdoor cannabis may die if the temperature drops below 40ºF. Some plants can withstand the cold, but their yields will be less than that of a typical plant because of delayed growth.
Just like with too much heat, the main problem with cold temperatures is photosynthesis. If it is too cold, your plant will not undergo photosynthesis, and the leaves will develop a purple color. Marijuana plants grown in cold weather are also more susceptible to mold.
In general, the best temperature to grow marijuana is about 68 degrees Fahrenheit during flowering, and 70-78 degrees Fahrenheit during the vegetative stage.
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Soil temperature and marijuana plants
Soil is a crucial component when growing marijuana, so you should make sure that you have chosen the best soil for cannabis growth. We recommend a Pot for Pot’s Superb Soil . It has the perfect balance of nutrients, perlite, and vermiculite to encourage proper soil pH, temperature, and drainage.
Soil is essential from the very beginning of a marijuana plant’s life. Marijuana seed germination is triggered when soil temperature, light, and moisture work together. For the best environment for your plants, consider investing in a soil thermometer to measure its temperature. The soil temperature should be maintained at 80ºF. This ensures that the roots stay warm. It also helps the stems and leaves withstand bouts of colder air (if you’re in an area that gets cool air). You can also place heat mats on the floor to maintain the soil temperature if your plants are not getting enough heat.
What marijuana strains grow well in hot temperatures?
Cannabis plants are hardy. Most marijuana strain will adapt to different climates and environments; however, some strains are better at it than others. When growing marijuana in a hot region, it’s best to choose strains that originated in similar climates.
Here are some marijuana strains that thrive in hot temperatures:
- Northern Lights is best cultivated in warm temperatures. It provides up to 22 ounces per plant.
- Amnesia Haze grows in hot and dry regions, preferably grown indoors with a controlled climate.
- Fruit Spirit thrives in areas where the temperature is hot. It can produce up to 19 ounces per plant.
- Tangerine Dream can be grown both indoors and outdoors as long as temperatures can be controlled. It produces high yields of about 18 ounces per plant. It reaches maturity in 9-10 weeks.
- Grape Ape grows best where there is both heat and sun. Grape ape produces high yields of up to 28 ounces per plant. It is mold and pest resistant.
What about humidity?
When growing marijuana in a grow tent, you must monitor both the marijuana grow tent temperature and humidity. The same is true when growing both indoors or outdoors; however, it is more noticeable in grow tents. Humidity is formed in the air the plants breathe out, as it contains water vapor. That’s why in a grow room, the moisture will always be at a higher percentage than temperature. This is because marijuana plants emit 90% of the water and only absorb about 10%.
High humidity levels are a problem for marijuana plants. Excessive humidity can slow your plant’s growth, encourage the development of mold, or even cause root rot. That doesn’t mean your plants want a desert environment, either. Excessively low levels of humidity can stunt growth and cause stress on the leaves.
Also, just like temperature , marijuana grow tent temperature and humidity needs differ depending on the plant’s growing stage. During the seedling stage, keep the humidity levels at around 65-70%. During the vegetation stage, humidity levels can lower to a range of 40-70%. Finally, once you reach the flowering stage, humidity levels should range between 40-50.
Near the end of your plant’s life, during the late flowering stage, humidity levels should range between 30-40%. Purchase a hygrometer to monitor the humidity levels of your plant’s environment.
Fixing and preventing marijuana heat problems
If you are growing indoors using a tent, the marijuana grow tent temperature is a crucial factor in whether your plants merely survive or thrive. To create and maintain the ideal temperature in a grow tent, start by ensuring you have ventilation. Fans are a great way to do this in a grow tent, or you could use air conditioning in a larger grow room. Your focus should be on any heat that is near your plants since excessive heat can cause heat stress. Most of the time, growing lights are the main heat source to be concerned about.
Maintain a cool environment by installing an exhaust fan to make sure that the hot air from the area is directed outside. To prevent smells from escaping with the heat, use an exhaust fan that has a carbon scrubber.
You can also fix a heat problem by situating the lights a little bit further from the plants. You can also use cooler lights. Air or water-cooled grow lights can protect the plants from heat, despite the light intensity. If using regular grow lights, keep them at least three feet away from your plants. Air or water-cooled lights can be placed as close as a foot away from your plants.
When outdoor marijuana plants are affected by heat stress, it can take several weeks to recover, so it is essential to prevent that stress in the first place. Luckily, protecting your outdoor cannabis plants from heat stress is almost the same method as protecting yourself – stay hydrated. Use micro-sprayers to cool your plants. This simple step can cool your plants by up to 30 degrees. You can also keep your roots cool by using fabric pots . This type of material allows your roots to breathe.
When you choose to water your plants can also help with absorption and prevent heat problems. To help keep your plants hydrated, water in the early morning before the sunrise and late in the evening after sunset. When you water at these times, your plants are better able to absorb more of their water because it does not evaporate as quickly.
Placing your plants in the shade can also help; however, you should only do this for the occasional heatwave. If your plants are not regularly exposed to direct sunlight, they may go into shock when they eventually are exposed to it. This includes moving your plants that are growing in containers.
You can also use seaweed kelp extract to protect your marijuana plants while they are recovering from heat stress. This ensures the plants are protected from the possibility of contracting heat stress in the future.
Growing marijuana is one of the easiest things to do; however, you’ll get the best results if you focus on creating and maintaining the correct temperature. Start with high-quality seeds or clones, Superb Soil , and a little bit of love, and you’ll be well on your way to growing healthy marijuana plants.
Temperatures and Medical Cannabis Growing: From Seedling to Harvest
The marijuana industry created an estimated $34 billion economic impact in 2018. Legal sales of marijuana are expected to increase from $10 billion in 2018 to $20 billion by 2022, according to the Marijuana Business Fact Book. This means that more and more legal growers (under strict governmental regulations) will be on the American horizon seeking the best indoor growing practices. Temperature and humidity monitoring are essential for growing healthy cannabis plants throughout the entire life of the plant…seedling to harvest.
What’s the Difference Between Temperatures and Humidity Levels?
Temperature and humidity levels interact and are very similar and are closely related to one another. Humidity is the measure of how much humidity is actually being held in the air. Relative humidity (RH) which is one way to measure humidity levels, is how much water is in the air compared to the maximum amount of water that can be held in the air at that temperature. The premise is that warm air holds more water vapor than cold air so it is important to get the warmest air in the environment. It is necessary to extract the warmest air from the growing environment while allowing cool air to enter. The warm air alone has way too much vapor for ideal growing conditions.
Horticulturalists know that the key to success in any growing plant is understanding the lifecycle of the plant. This is also true with growing cannabis. Throughout every stage of growth, cannabis plants will have a constant need for water which the amounts will fluctuate with the humidity. When the humidity is high, plants use their leaves to absorb moisture from the air which results in less water drawn from their roots. On the other hand, when the humidity is low, cannabis plants will take more water through their roots.
Monitoring and having the right humidity encourages strong, healthy, nutrient-dense leafy plants with optimal growth.
Humidity levels must be monitored to prevent:
1. Bud Mold/Rot: A condition when the inside of the plant is taken over by mold. When this happens the buds are unusable.
2. White Powder Mildew: White Powder Mildew (WPM) is a rapidly reproducing fungal disease resulting in a white powder or mildew covering the plant. If caught early enough, it can be prevented, if not the plant will become unusable.
3. Nutrient Problems: If a cannabis plant takes in too many nutrients at once the leaves will turn yellow and the tips will look burnt, called nutrient burn or nute burn.
4. Slowed Growth: If humidity levels are not optimal for the growth stage, they don’t grow as fast as they could. Younger cannabis plants grow better in higher humidity than more mature plants.
So, the next question is how do you measure the ideal levels?
Cannabis Temperature Monitoring In All Stages of Growth
There are four stages or periods of cannabis growing, all requiring different temperature and humidity levels. They are seedling, vegetation, flowering, and late flowering. Experts recommend monitoring levels throughout all four stages using a digital thermometer and a digital hygrometer that include a memory feature so history can be reviewed. The four stages and what they require are:
1. Seedling Stage: Seedlings or clones, little cut-off pieces from a parent plant that needs to develop roots, require high humidity levels between 65 and 70 percent. These high humidity levels are needed because the root system is not established and humidity allows water intake through the plants’ leaves. Young growing cannabis plants prefer temperatures between 75 and 80 degrees Fahrenheit. Anything above 80 degrees Fahrenheit is not recommended.
2. Vegetation Period: This is the stage that cannabis starts developing its renowned leaf shape. It is important to note that light exposure is a very important part of this stage. The number of humidity levels should be lowered by five percent each week throughout the vegetation period. The temperature can be increased, too because roots absorb more water and evaporate through the plants’ leaves. Humidity levels should be before 40 and 70 percent. If wet spots are forming on the leaves, humidity levels are too high.
3. Flowering Plants: The humidity levels of cannabis plants at the beginning of the flowering stage should be lowered to 40 to 50 percent. At this stage, the plants have created a robust root system to meet their water needs. They still absorb water through the leaves. A lower humidity level is required to prevent mold and mildew from forming. Note that mold and mildew infect the plant from the inside the buds, so it isn’t visible at first.
4. Late Flowering Period: This period lasts anywhere between six and 12 weeks and when plants mature. During this time careful temperature and humidity monitoring are necessary. It is recommended that humidity levels be lowered between 30 and 40 percent to improve the yield, flavor, and appearance of the plant. Temperatures can range between 70 and 80 degrees Fahrenheit.
Tips To Adjust Temperature and Humidity for Cannabis Growing
It can be difficult to keep humidity and temperature levels at the right balance throughout the plants’ life cycle. Keep in mind that warm air retains more water than cold air and that relative humidity and temperature interact to create the perfect balance. The following are hands-on tips for adjusting these levels but note that there is technology available in the SaaS Cloud that will wirelessly do the work for you.
Tips to Lower Humidity and Temperature:
- Increase fresh, cool air in the growing area
- Water plants right when lights are turned on in the growing area
- Add a dehumidifier to regulate humidity in the growing area
Tips to Increase Humidity and Temperature
- Keep the soil surface moist
- Surround the room with moist towels and open containers of water
- Use a humidifier to constantly add moisture to the room
It is difficult to be present for the entire life cycle of a cannabis plant. There are more innovative and technological methods for monitoring temperature and humidity levels. Contact SensoScientific for a free trial and to learn more about the most advanced wireless monitoring solution available for cannabis temperature monitoring.