Best Temp And Humidity For Germinating Weed Seeds


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Discover more on how to control your grow room’s environment and how grow lights play a role in the ideal temperature for growing weed. How to measure and adjust humidity levels in your marijuana grow room? A guide with a schedule for the best humidity levels for your grow. 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

The Best Temperature for Growing Weed

Growing marijuana isn’t simply putting some seeds in the soil and watching them grow. Weed needs nutrients, water, proper growing material, good pH levels, ventilation, pruning, light, and space, just to name a few. So, does the temperature for growing weed matter?

Yes! One of the most important aspects of growing cannabis is the temperature of the indoor or outdoor garden. Weed likes a specific climate to create a reasonable yield without problems.

Continue reading to find out everything you need to know to create the perfect climate for your marijuana plants.

Why marijuana growing temperature matters

Temperature for growing weed matters because it’s linked to the health of your cannabis plants. When the environment isn’t quite right, the marijuana crop will have a small yield or be more prone to diseases.

Some hybrids are fragile and can’t take any extreme temperature changes without dying. Other cannabis strains are heat resistant or more stable. Even then, their maximum yield can be lower if not cultivated in the correct climate.

The best temperature for growing weed at different stages

The temp for growing weed should be between 65 to 85 degrees Fahrenheit, and marijuana crops prefer specific climates during the different growth stages.


At the seedling stage, marijuana likes it hot and humid. The best temp for growing weed indoors or outdoors is 70 to 85 degrees Fahrenheit with a 75 to 85% humidity level.

During this time, the cannabis seeds are growing roots and need to absorb extra moisture because of the rapid growth. Make sure the humidity level never goes over 90%, as this will welcome mold, mildew, and other pathogens.


The next phase of the weed growing cycle is the vegetative stage. The marijuana growing temperature needs to drop a little to 70 to 78 degrees Fahrenheit during the day. At night, it never should drop more than 10 to 15 degrees.

In the vegetative stage, you’ll start to reduce the humidity by 5% every week until you get to the range of 45 to 55%. By doing this, you’re preventing the risk of bud rot or damping-off.


The flowering stage is the last part of the marijuana plant’s life. During this time, you should reduce the cannabis temperature again to 68 to 75 degrees Fahrenheit. Keep an eye on CO2 levels, as this can increase the heat throughout the day.

You’ll need to lower the humidity level an additional 5% each week until it’s at 35 to 45%. During the last two weeks of growth, the moisture needs to be about 30%. Monitoring the humidity level will keep powdery mildew or other pathogens at bay.

How to control marijuana growing temperature

We’ve gone over the numbers, and now it’s time to tell you how you can achieve the best temperature for marijuana growing.

You can control indoor cultivating spaces easier because there are fewer elements you have to deal with. If you have central heating, you can use this to regulate the temperature. When this isn’t an option, you can buy a space heater. Remember, lights put off extra heat.

With artificial heating, it tends to create a dry environment. Make sure you have a humidifier in indoor gardens. Also, you’ll need some grow tent ventilation within the space to help reduce the temperature or humidity when required. This will also help with how to get rid of weed smell that lingers.

You’ll have to deal with natural sunlight, wind, rain, clouds, and changing temperature from day to night with outdoor gardens. To regulate the heat within the greenhouse, you can purchase an outdoor space heater.

Keep the humidity levels in check with a humidifier or by having buckets of water around so that the moisture will naturally be in the air. Use a ventilation system to help regulate the heat on hot and humid days.

With an indoor or outdoor growing space, you’ll need a high-quality thermometer and humidity checker.

Correcting temperature for growing weed

If there’s an issue with the climate in your marijuana growing area, you’ll need to fix it before any damage happens to your weed plants.

Temperature too low

When the climate is too cold, it stunts the growth of your cannabis plant, and your yield will be low. If the temperatures drop below freezing, your crops might die.

If you notice the temp dropping, slowly increase it by turning on your heating system. Then, look for the cause. Maybe there’s a crack in a window or a problem with the ventilation.

Temperature too high

Marijuana likes the heat, but too much of a good thing can damage the plant. Pathogens are quick to attack vulnerable weed crops.

Along with that, an excess of heat can hinder the harvest’s ability to perform photosynthesis, which harms the marijuana plant’s growth. Signs of cannabis heat stress are drooping, cupping, or yellowing leaves.

Temperature and humidity

Temperature and cannabis humidity levels are linked because the warmer the air, the more moisture it can hold and vice versa. This is important because you need the correct percentage to be balanced to produce a quality marijuana plant.

This table will give you an idea of what to expect at certain temperatures.

Stage Temperature Humidity
Seedling 70 to 85°F 75 to 85%
Early Vegetative 70 to 80°F 60 to 80%
Late Vegetative 70 to 80°F 45 to 55%
Early Flowering 65 to 80°F 35 to 45%
Late Flowering 65 to 80°F 30 to 35%
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Temperature and choosing the best grow lights

All lights give off a certain amount of heat. When you’re growing indoors, this is a factor you’ll need to consider.

You don’t want grow lights that give off too much heat because the leaves closest will be at a higher temperature than the rest. Try to look for lamps that don’t change the environment too much.

Ideally, you want the temperature to be consistent in all parts of the room.

Final thoughts on the ideal temperature for growing marijuana

When you’re a weed grower, you have to keep in mind many factors. One of the most influential aspects is the temperature of the growing space.

When the temp is perfect during the different stages, your cannabis crop will yield the proper amount and be less prone to diseases.

Now that you know all this information check the temperature and humidity levels in your garden. If you haven’t started planting yet, buy some cannabis seeds and use these tips on your way to becoming a successful marijuana grower.

Visit our shop to get the best deals in marijuana seeds! We offer the best genetics and a germination guarantee, so why look anywhere else for your favorite strains?

About the author: Derek LaRose

Also known as Kronic from The Cannabis Kronicles, Derek LaRose is a young ambitious cultivator and a staple educator for indoor cultivation.

Marijuana humidity

We are going to take some time to delve into some much-needed information to further your understanding of the importance of humidity for seedlings when growing marijuana plants.

What is humidity

Humidity is expressed as the quantity of water vapor in the air. Humidity plays a necessary role in influencing how much evaporation occurs in cannabis plants.

Your plant will take in more nutrition and water when the humidity is low.

If for any reason the evaporation strain gets to be too much, marijuana plants will guard themselves against scarcity by closing their stomata. So naturally, this will stunt the growth of your plant due to the lack of water absorption.

This is why you must have the proper humidity levels in your marijuana factory. When the plant is in the growth stage, it will need high humidity, unlike the blooming phase.

This is mainly because the roots of baby plants are much smaller. Measure the humidity using a hygrometer. In the first stages of growing your plant, the humidity can be about 70%, and you can reduce it by 5 every week until it gets to 40%. Included in this article is a helpful schedule to assist you with the right information on humidity levels for both indoor and outdoor growing.

Relation to temperature

Before we go any further, we have to discuss the connection between temperature and humidity. First you must understand that the percentage of absorbable water is determined by the temperature. At the temperature of 68 degrees Fahrenheit, air can take in up to 7.2 ml of water. In this case, air has a corresponding humidity of 100%.

With temperatures and humidity such as that you are guaranteed to see absolutely nothing because the water vapor is very high. At 32 degrees Fahrenheit, the air will take in around 5 ml of water. For this reason, air is much drier during the winter time than the summer months.

‘The hotter it is, the more moisture the air could hold at the same temperature.’

Jorge Cervantes

Since you will be airing out your grow room quite frequently, you will end up releasing the humidity as well. So you have to be sure that your marijuana factory is always moist so the humidity level goes up. Later in the article you will be informed of options for adjusting the humidity levels.


At first, your marijuana cuttings will have very small roots so they are not able to take in much water yet. At this stage, you want them to evaporate a very small amount of water. Cutting will only evaporate a small amount of water when the humidity is high, and require fewer roots.

Another way to reduce the amount of evaporation is chopping the bigger leaves halfway from the cutting. A humidity of 70% is exactly what you want when putting the cuttings in your marijuana factory.

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Your cuttings will begin growing roots in a clone box when the temperature is around 71.5 degrees

Fahrenheit in a very humid environment and fluorescent lighting.

I suggest the cuttings go beneath a 600-watt HPS lamp in an environment with 30% humidity for good results.

For as long as the 2 nd or 3 rd week of blooming the roots are going to grow the size of the actual plant. The roots must be durable for proper water and nutrient absorption.

If you’ve produced a bountiful harvest with your desired attributes, cloning these marijuana plants is the next best thing to do so you can recreate the same results.


Seedlings require a separate set of rules since they have a taproot at germination that takes in moisture and grows fairly quickly. Never clip the leaves of a seedling. The leaves are necessary for absorbing light and evaporating water.

To help the seedlings take in water and nutrition through its leaves, have the humidity at high levels. Begin at 60% and slowly work your way down to 40%. Click this link to buy marijuana seeds

Flowering stage

As your plant start flowering, you can gradually decrease the humidity level.

At this stage the roots are very mature, so the plant is able to take in the most nutrients and water. You will want to reduce the humidity level in the flowering stage since mold has a tendency to flourish in high humidity environments.

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With age, there is a higher chance of your marijuana plant getting mold.

As a result of the high humidity, water gathers around the tops and that when mold has the opportunity to develop. Bud rot is the most frequent type of mold.

Levels of humidity in cannabis plants

Once the plant is fully grown you will need to start thinking about harvest time. Our free little Harvest Guide will help you determine the best moment to cut your plants.

Follow this schedule to ensure you give your plants the right amount of humidity for optimum growth. Notice there is a difference in clones and seedlings.

Clones humidity level

Growth Week 1 70%
Growth Week 2 70%
Flowering Week 1 65%
Flowering Week 2 60%
Flowering Week 3 55%
Flowering Week 4 50%
Flowering Week 5 50%
Flowering Week 6 45%
Flowering Week 7 45%
Flowering Week 8 40%
Flowering Week 9 40%

Check this complete Marijuana Grow Schedule with temperatures, humidity, watering and nutrients tips.

Seedlings humidity level

Growth Week 1 60%
Growth Week 2 60%
Flowering Week 1 55%
Flowering Week 2 50%
Flowering Week 3 50%
Flowering Week 4 50%
Flowering Week 5 50%
Flowering Week 6 45%
Flowering Week 7 45%
Flowering Week 8 40%
Flowering Week 9 40%

How to raise the humidity in your grow room

So, you have a few options for raising the humidity in your grow room. For starters, you can try spraying water on the walls and flower.

Also, try putting the lights further up so the temperature will go down a little near the plants. This way you won’t have to turn on the extractor fan as often. If you put bottles or buckets of water around the grow room, or even wet towels, this will raise the humidity level.

How to decrease the humidity

Dehumidifiers are most certainly your best option. It has the capability of taking moisture from the air and draining it or holding it in a reservoir. Make sure to get a larger humidifier because the smaller ones fill up quickly.

Once your marijuana plant starts flowering the humidity will need to be decreased, so it is necessary to dehumidify. Try using the extractor fan on a higher setting than usual or even you can even shoot cold air into the room.

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Keep in mind that the humidity outside may influence the humidity in your marijuana factory. For instance, if on a rainy day the humidity increases quickly, you can shut off the extractor fan or turn it to a much lower setting. Make sure the temperature doesn’t rise too quickly because you’re getting less cold air from outside.

How to measure humidity levels

Hygrometers are used to measure humidity levels (wiki on hygrometer at this link). All you have to do is put it over the plants, so long as it is in an area that easily aired out. The analog hygrometers cost $5 and you can buy a digital one for $10.

The higher priced hygrometers are usually of better quality. For ease of use, get the one that has a wire attached to it. This makes it easier to see the humidity without having to turn the lights on in the room. These devices have a built-in storage bank that tracks the highest and lowest values, to help you determine how well you stayed within the preferred range. Buy the best hygrometers at this link.


Watering your plants causes the humidity to go up quite a bit, which is fine when in the growth stage because you just spray the floor and walls to raise the humidity. During the flowering stage, humidity levels often go up way too much after you water your plants.

Once the lights are no longer on in the grow room, the temperature decreases and extracting a lot of hot air is unnecessary, which usually is the cause of humidity increases.

Nourish your plant with water once the lights are on, that way they will evaporate most of the water throughout the day. Understand that spraying water on top of the buds is pointless because you will raise the possibilities of the humidity rising and leading to mold.

Outdoor plants

Humidity is much less of an issue when growing your cannabis plants outdoors. The springtime and the start of summer offer higher humidity which works just fine since there are no buds present on the plant for moisture to gather. Any moisture on the plant from morning dew will easily evaporate throughout the day.

Once Summertime ends, the flowering stage starts and there is a shift in the climate, resulting in cooler days and more rainfall. This usually makes the humidity higher. In the cooler months, the morning dew could be an issue since the sun is not guaranteed to come out and the temperatures are sometimes too low to evaporate it.

Luckily a tad bit of rain will not cause the buds to rot, but just in case you may want to be on the lookout for this. In the last of the blooming stage, it might be a good idea to brush the dew off your marijuana plants in the mornings. If you notice that rain is expected, go ahead on move your plants to a location where they will be kept dry, away from the rain. It is always best to take the necessary precautions.

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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.

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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:

  1. Increase fresh, cool air in the growing area
  2. Water plants right when lights are turned on in the growing area
  3. Add a dehumidifier to regulate humidity in the growing area

Tips to Increase Humidity and Temperature

  1. Keep the soil surface moist
  2. Surround the room with moist towels and open containers of water
  3. 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.

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