What is the Ideal Temperature to Grow Marijuana?

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Have you ever heard someone say “growing pot is easy, it grows like a weed”.

Yah that’s not true.

Anyone can throw a few seeds in the dirt outside and water them. You might get decent product like 10% of the time.

But seeds are expensive.

And if you want to consistently grow high quality weed with big yields, you need the right conditions for your plant.

The temperature of your grow room is extremely important for the health of your plant.

Cannabis thrives in temperatures between 70–85°F (20–30°C) during the day. Most growers try to maintain a temperature of about 75°F (25°C).

In the night when you have your grow lights turned off, cannabis plants do best with temperatures that are around 62-68°F (17-20°C).

Too hot, it dies.

Too cold, it dies.

In this article, we’ll cover what you need to take into consideration for temperature when you’re growing weed and tell you exactly what temperature you should use for growing marijuana.

In truth, many people wonder what it’s like to grow weed for a living, especially with marijuana being legal in so many states. In addition, there are many questions and concerns for first time growers such as what the humidity and temperature should be for spacebuckets and other the temperature for environments.

The Best Temperature to Grow Marijuana: Grow Room Temp & Humidity

Although growing marijuana is pretty simple, there are a few things that are crucial for a plant’s health such as temperature and humidity. In fact, getting the right temperature is very important.

The temperature affects your plant’s ability to grow and synthesize sugars or other elements through photosynthesis.

Basically, photosynthesis is the method that plants and other organisms use to transform light energy into chemical energy. As result, the chemical energy is stored in a carbohydrate molecule to be used when needed like sugars and other elements.

For example, sugar is synthesized from carbon dioxide and water when it goes through photosynthesis.

Additionally, oxygen is typically released as a waste product. However, without photosynthesis, the oxygen content cannot be maintained.

Marijuana, cannabis, pot or weed plants growing indoor


Should You Grow Your Marijuana Indoors or Outdoors?

One of the biggest concerns for first time growers is whether to grow their plants indoors or outdoors. On the other hand, the decision does not have to be immediate since you can start your plants indoors then move them outside at a later time.

There are actually several pros and cons for growing indoors and for growing outdoors.

Indoors – Pros and Cons


  • Grow time is shorter
  • Growing is more discreet and hidden from view
  • Can have numerous crops a year with the potential of a continual crop
  • Environment control is easier which often produces a consistent high quality bud


  • Start-up costs are high
  • Requires more maintenance than growing outdoors
  • Good ventilation and a clean area are vital for optimum growth
  • Overhead is high such as electricity or utility costs, system expansion, etc.

Outdoors – Pros and Cons


  • An easy method with minimal maintenance
  • Inexpensive start-up costs – free ventilation and light
  • Generally higher yields when compared to growing indoors
  • More space to grow with limitless sunshine (weather permitting)


  • Unrealistic for people who live in a city
  • Water source needs to be close by or it has to be carried to the grow area
  • Elements are unpredictable like early frost, drought, heavy downpour etc

What Temperature Is Too Cold for Plants Outside?

For the most part, marijuana is pretty robust and resilient. However, keeping the ideal temperature is important if you want optimum growth and higher yields.

If the temperature falls below 40°F (4°C), your plants will be highly stressed.

This can cause them to lose leaves or stop absorbing nutrients.

Temperatures below 59° F (15°C) will cause everything to slow down which means lower yields. They can recover from this pretty easily but it will have a negative impact on the plant.

What is the Ideal Temperature to Grow Marijuana?

Additionally, if plants are exposed to the cold for a long time, the buds can easily be damaged, growth can be slowed, yields are drastically reduced, mold easily breeds, and possible death.

Raising the Temperature of Your Grow Room

When temperatures get too cold outdoors, growers can help keep their plants warm with various techniques like a portable gas heater, insulation like polyethylene plastic, or place them inside if your plants are in containers.

Likewise, the temperature can be raised in your grow room using various methods like

  • Install extra insulation
  • Use a stronger and hotter grow light
  • Use reflective insulation to emit more heat
  • Grow strains that are more resistant to colder temperatures
  • Makes sure that the roots say warm and are off the cold floor
  • Keep the grow lights on at night and off in the day for best efficiency
  • Be careful and not allow hot air to directly blow on your plants – it can burn or destroy the leaves and buds

What Happens When the Temperature is to Hot?

Generally, high temperatures are a lot less of an issue for cannabis growers than low temperatures.

Marijuana plants love the heat.

However, temperatures that are higher than 85°F (30°C) will play havoc on your plants.

When cannabis is overheated your plants growth and maturity will considerably slow down. In addition, the excess of heat can attract various pest and diseases such as spider mites and powdery mildew.

Background Canopy of Budding Indoor Marijuana Plants

Too much heat along with extra humidity causes a ton of other issues.

For instance, with the lack of extra ventilation, condensation builds up and mold or bud rot can quickly develop.

Mold is a crop killer and will ruin an entire grow tent full of weed. 

Additionally, you have to water your plants more often because the soil dries out at a much faster rate. In turn, the cost to water your plants is much higher.

Water might be cheap, but if you’re supplementing with nutrients, you’ll be using a lot of nutes and wasting a lot of money.

How to Detect Heat Stress on Your Cannabis Plants

When a plant is exposed to too much heat, it can cause irreversible damage and sometimes even death. Unfortunately, high temperatures can sometimes go unnoticed, especially if you’re a beginner.

However, there are numerous heat stress symptoms to watch for

  • Leaf edges curl
  • Brown or burnt leaf edges
  • Drooping and wilting leaves
  • New, higher growth is affected
  • The whole plant droops and wilts

In addition, plants that are outdoors can also be exposed to excess heat. Some of the symptoms include leaf edges curling, plant wilting or drooping, and burnt leaf edges.

Hand Holding Big Cannabis Bud. Medical Marijuana

As well, there may be spotting and discoloration like brown or yellow. Extremely low humidity can also cause your plants to get heat stressed.

Your plants environment may not be super-hot, but the low humidity will cause your plant to be exposed to dry, hot air. In turn, the low humidity can cause similar symptoms of heat stress such as the leaf edges curling or turning brown.

How to Lower Grow Room Temperature

Your plants can easily be stressed if the grow room temperature are too high. Fortunately, there a several things you can do to lower the temperature.

  • Use a dehumidifier
  • Install an air conditioner
  • Plant a heat resistant strain
  • Check or install your exhaust system
  • Utilize an evaporative cooler (swamp cooler)
  • Make sure that there is proper air circulation
  • Get smaller grow lights that produce less heat
  • Change the light schedule so that the grow lights are off during the hottest part of the day

How to Monitor the Temperature for Growing Marijuana

Cannabis, marijuana, and hemp all require the right temperatures for optimum growth. Exposure to both high and low temperatures not only stunts the growth of your plants, but can do considerable damage and sometimes cause death.

Nevertheless, there are numerous ways to keep the proper temperatures so that your plants can thrive and grow healthy buds.

  • Install the right sized HVAC system
  • Set up horizontal air flow (HAF) fans
  • Makes sure to measure the temperatures correctly
  • Utilize shade curtains during the hotter part of the day
  • Buy a thermometer that measures both the temperature and relative humidity (RH)
  • Makes sure that you have the proper heating and cooling capacity in your greenhouse

Grow Room Temp and Humidity for Various Growth Stages

The ideal temperature range not only fluctuates from daytime to evening, it is also different during each stage of plant growth. As well, relative humidity is different with each stage of growth.

  • Vegetative stage – 70-78°F (21-25°C) during the day and 10-15 degrees cooler at night. RH levels should be 45-55%
  • Flowering stage – 68-75°F (20-23°C) during the day and 10-15 degrees cooler at night. RH levels should be 50-60% during early flowering and reduced to 40-50% for late flowering

Grow Tent Temperatures for Dark Periods during the Vegetative Stage

Similar to the temperature for plants outdoors, you don’t want your indoor plants to be too cold during the dark period of growing.

Grow tent temperatures during the dark periods of the vegetative stage should be between 62-72°F (16-22°C). If the temperatures reach outside the guidelines, your plants could suffer immeasurable stress or stunted growth.

Marijuana and Cannabis growing indoors in a tent

In fact, it can change the potency and flavor of the buds. As well, intense hot or cold temperatures can sometimes destroy the buds. Just make sure that the temperatures are not too extreme between the day and evening hours.

The Perfect Solution

As many experts suggest, grow temperatures for marijuana should be around 77°F (25°C). However, this number can change depending on the strain and environmental conditions.

Just remember, if you are a novice or you are working with a new strain, don’t be afraid to experiment a little on the temperatures and humidity. As well, closely monitor any changes of your plants whenever you alter the growing conditions like the temperature or other factors.