Best Temperature To Grow Weed

If you are a seasoned marijuana grower, you know that cannabis enjoys a comfortable room temperature, especially when growing indoors.

Conditions should be warm but not too humid. If growing indoors, and that’s all you need to worry about.

If the grow room feels too hot or cold for you, then it is probably too hot or cold for your marijuana as well.

The question remains, what is the optimal temperature for growing marijuana?

Ideally, marijuana prefers temperatures in the 70 to 85°F range. This is especially during the day when the lights are on. At night when the lights are off, they are happy with slightly cooler temperatures.

The following guide will take a closer look at how to grow marijuana in the perfect temperature range.

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Why Is The Temperature Important For Growing Marijuana?

Growing Room Temperature

Temperature is vital if you want to grow a cannabis garden that is thick, luscious, budding, and produces excellent quality yields.

This means that you need to maintain the temperature in your grow room at all times.

When growing marijuana indoors, the temperature control factor is going to be one of the main aspects that distinguish how your marijuana will grow.

There are lots of things to consider when maintaining the temperature such as where your grow room is situated.

Marijuana plants prefer decent temperatures and need the ideal climate in order to thrive.

For this reason, you want to grow marijuana plants with high levels of THC and ideal temperatures at all times.

Marijuana plants enjoy temperatures of between 75 to 80° F when they are small.

Once they start entering the vegetation stage, you need to provide them with at least 82°  F maximum.

At nighttime, the temperature should naturally be lower, but the difference between the day temperature and night temperature should never be more than ten degrees celsius.

In fact, maintaining a difference of 5 degrees Celcius between day and night is essential.

This is so crucial because cannabis plants rely on heat for photosynthesis. Light needs to be present in order for your plants to feed, and heat is a natural consequence.

If there is not enough heat and the temperatures are too low, then there is not enough evaporation happening in the leaves.

The evaporation process is crucial for assisting the suction force required to nutrients from the roots to the leaves.

So the less evaporation, the fewer nutrients are being sucked up to the leaves.

Ultimately, the overall impact is that your plants will grow into smaller cannabis trees as opposed to bigger ones.

In the latter stages, this has various types of consequences such as overload of nutrients in the soil; however, not enough in the plant material itself.

Ultimately this leads to excessive acidity in the ground, and this brings with it a wealth of other problems.

On the other hand, temperatures that are too high or humid have consequences too.

Plants may not die, but they will grow very slowly.

When it’s too hot, cannabis plants are also susceptible to certain issues such as white powdery mildew.

Therefore, maintaining the ideal room temperature inside your grow area is crucial for the overall health, growth, and development of your cannabis.

Measuring Temperature

In order to get an idea of the exact temperature in your program, measure it at different locations.

The temperature needs to be ideal in range, and it needs to be equally dispersed.

In order to get accurate readings, take your thermometer to various spots in the growing area, and be aware of places that are too hot.

In order to be sensible, don’t measure temperature beneath the light.

This can give inaccurate readings since light bulbs emit heat.

Be sure that you’re holding the thermometer in the shade as well.

The heat given off from the globe is not the same as the room temperature, and what you are looking for is the precise temperature inside the room.

It would help if you also were mindful of exactly where the light bulb is situated.

If it’s too close to it will cause burn on the top of the leaves.

If the temperature in the shade is ideal, but the light bulb is too close to your plants, it is definitely going to cause some damage.

What Are Some Problems Connected With Cold Temps?

Cannabis On Cold Temperature

When temperatures in your grow room are too cold, it can be just as detrimental to your marijuana as high temperatures.

Unlike high temperatures, though, cold temperatures can shock your plants and possibly even cause them to die.

So as a rule of thumb, avoid growing marijuana in temperatures that are below 59° F.

Your plant will definitely struggle to control cold temperatures like these and ultimately will die.

Cold temperatures deter natural photosynthesis, just like hot temperatures do.

The enzymes responsible for the light-independent reactions of this process will become less active in low temperatures, so your plants will grow, but they will do so at an extremely slow rate.

Low temperatures believe it or not can also create the perfect environment for mold and mildew.

Mold prefers cold and damp environments and may form on your leaves, buds, and stems as well.

So if temperatures drop to an unacceptable range, mold can become an issue that wreaks havoc on your marijuana garden.

Cannabis plants do prefer slightly cold temperatures at night; however, it should never be too cold.

Certain marijuana plants will develop a beautiful looking purple and blue hue you when they’re grown at low temperatures and ultimately, this makes for beautiful buds when you are harvesting.

However, the ability to develop these hues depends on genetics as well and are not entirely related to the room temperature.

Overall speaking, cold temperatures are extremely hazardous to your marijuana garden and should be avoided at all costs.

What Are Some Problems Connected With Hot Temps?

Marijuana Plant Powdery Mildew

Hot temperatures are none the better.

Although hot temperatures or high temperatures are less of a concern than cold temperatures, cannabis plants prefer an ideal temperature to thrive.

It’s usually not heard of that plants die from too much heat; however, temperatures that are over 100 degrees Fahrenheit will cause your plants to grow slower.

This is mainly because the enzymes that play a role in photosynthesis are not able to work effectively.

Aside from stunting the growth of your marijuana garden, heat will attract pests and diseases.

White powdery mildew and spider mites can tend to become one of the biggest issues you’re facing when growing marijuana in extremely hot conditions.

High temperatures will also cause water to evaporate from your soil quicker.

So you need to water your plants more often, and they may also struggle to absorb the nutrients in the soil.

Eventually, this can lead to nutrient burn, which ultimately will damage your foliage and roots.

High temperatures that are combined with high levels of humidity also expose your plants to additional issues.

If you’re growing your marijuana garden in hot and humid conditions and there is not enough ventilation and circulation, your plants will suffer from root rot or mold.

This eventually puts too much stress on the plant and essentially destroys the buds that you’re working so hard to grow.

What Are The Optimal Temperatures At Different Stages Of The Growing Process?

Now that you understand the overall preferred temperature of your marijuana plants, you also need to understand the preferred temperature at different stages of your marijuana plant lifecycle.


Thermometer In Cannabis Grow Room

Clones prefer a temperature that is between 70 to 85° F with high humidity levels.

Since clones don’t have a root system as yet, they get all of their water via transpiration of the leaves.

This process occurs until the roots are fully formed.

Therefore, clones prefer human conditions with plenty of water to be evaporated into the air.

So many people use a humidity dome, which artificially raises the humidity for clones.

They also grow faster when the temperature is slightly warmer at about 70 to 85° F

Seedling And Vegetative Stage

70 to 85°F is a preferred temperature range with low humidity.

Seedlings prefer high temperatures with high humidity.

However, if you can achieve this while they are seedlings, as they grow older, even if the temperature fluctuates slightly or humidity drops a bit, it will not affect the growth and development.

Cannabis plants are able to withstand the cold and dry conditions even as it ages.

Outdoor plants are naturally more resistant and tougher when it comes to temperature fluctuations than indoor plants.

With indoor cannabis trees, it’s best to aim for temperatures between 70 to 85°F.

During this vegetative stage as well, these temperatures are recommended as it gives plants the ability to flourish.

Cooler temperatures are recommended during darker periods as well.

At night, cool temperatures will promote faster growth during the vegetative phase for your marijuana garden.

Flowering Stage

Using Thermometer For Weed

Temperatures between 65 to 87 degrees Fahrenheit with low humidity is preferred during this stage

During the flowering stage, temperatures should be kept under  80°F throughout this stage unless you are supplementing your marijuana with CO2.

One of the most crucial factors during this stage as far as temperatures go.

Keeping temperatures below will help your plants become more potent, have prettier buds and also an abundance of trichomes.

This is ultimate because high temperatures during that stage cause plant problems and slow down growth.

It also causes terpenes to evaporate.

So if your room temperature is too hot during the flowering stage, it could be burning away the terpenes, which gives your marijuana the flavorful taste and smell.

To ensure that plants are not exposed to high temperatures after the sixth or seventh week off flowering because this is the stage when the terpene content in your body really starts to multiply.

Drying And Curing

Starting with good genetics and giving your plants ample nutrients is the best way to get a bountiful harvest.

However, the drying and curing stage is crucial as well.

Buds that are dried and cured efficiently are more potent, look better, and are smoother to smoke than those that haven’t been cared for as well.

In order to dry and cure your buds, maintain the proper temperature and humidity during this process as well.

During this stage, if you keep temperatures optimal, you don’t have to worry about mold or over-drying, and you get perfectly good buds each and every time.

How To Control Temperature In A Grow Room?

Step 1

Modern Digital Thermometer

It’s important to measure the temperature inside your grows room, but it is also to know essential to know what the relative humidity of your grow room is.

So to do this, you need to get a tool that allows you to measure both humidity and temperature simultaneously.

Ultimately you need to find a thermometer that works accurately.

There are cheap ones on the markets; however, they are a few degrees off and do not give you an accurate reading.

So it is recommended that you purchase two or three of these thermometers and use the average to determine what the actual room temperature is.

However, if you do have a budget for it, go ahead and invest in a thermometer of the highest quality.

Step 2

Download a temperature chart online or write down the recommended temperatures for each stage of your marijuana plant life.

Step 3

Next, once you have purchased a thermometer, used it, and gotten an average reading, you want to correct temperatures that are either too high or too low.

There are various tools available to help you control your room temperature. One solution is investing in an all in one air-conditioner.

Too Hot

Ensure that your grow room is equipped with an excellent exhaust system that draws out hot air and increases circulation to your marijuana plant.

If you don’t have an exhaust fan that’s drawing out the hot air from your grow lights, correcting that will be your first step.

An exhaust system is crucial as it keeps temperatures down and it will also improve the air quality for your plants to thrive.

Air Circulation

Ensure Air Circulation How To Make Buds Bigger During Flowering

If there is not enough good circulation inside the room, then there’s likely to be hotspots that will damage your plants.

Using fans is a great way to not only get the air circulating but keep temperatures down.

Ultimately it’s crucial that you remember not to point the fans directly at your plants.

Your leaves should be slightly rustling and never ever waving around.

If your leaves are waving, that means that your fan is either too close to the plant or it’s on a very high setting.

Change The Light Schedule

If it is getting too hot during certain parts of the day, then you need to adjust your light schedule so that the grow lights are turned off during the hottest parts of the day.

During the vegetative stage, plants require approximately 18 hours of light by day.

If it gets too hot in the middle of the day, you can switch the lights off for six hours during that part of the day.

However, this strategy may not be effective in resolving the main problem, but it will alleviate heat stress.

Investing In Different Grow Lights

It is possible that grow lights could be affecting the grow room temperature, and if that is the case, then you need to use your dissection and invest in different grow lights.

Other Ways To Cool The Air

If you have good air exchange and you’ve tried all of the above steps, but the temperatures are still too high, then you should use a proven air cooling method.

And perhaps one of the most effective and foolproof ways of doing this is by installing an air conditioner.

What To Do When Temperatures Are Too Cold?

Marijuana LED Grow Lights

If it’s too cold in your grow room, then besides getting a heater, you should invest in a stronger grow light in addition to insulating and containing the heat.

Plants should be insulated from the cold, and this is the first step in eliminating cold room temperature.

It’s cheaper to insulate a small space; however, you must create a dedicated grow box as well.

Insulating materials are affordably priced and can be found at local home improvement stores; ultimately, you use this to insulate your growing area, and this will keep the cold air outside and the hot air inside.

Once you have a properly insulated the grow area, your grow lights will provide enough heat to keep the cannabis plant warm enough so that they can grow and thrive.

Related Questions

How Important Is Maintaining An Optimal Room Temperature When Growing Cannabis?

Maintaining the ideal room temperature when you’re growing marijuana indoors is absolutely crucial to your plants’ growth and development.

It can mean the difference between succeeding and failing as a marijuana grower.

How Can You Determine The Indoor Room Temperature?

There are various tools that you can use, such as a thermometer to measure the temperature and humidity levels inside the grow room.

How Can You Maintain Or Control The Room Temperature In Your Grow Room?

When temperatures are too cold, you can invest in insulating supplies, heaters, and stronger grow lights to increase the heat inside this room.

When the room temperatures are too hot, then you can invest in fans, increase ventilation, and air circulation or ultimately buy an air-conditioner to control the temperatures indoors completely.

James Alexander James Alexander
Hey, I'm James! The founder and head writer here at I started this site to share my passion and knowledge of all things cannabis. I used to work as a budtender in central Amsterdam, and have over 7 years of growing experience.

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