The temperature for germinating cannabis seeds is best at 78° F (25° C) because both low and high temperature impairs germination and growth. The best 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. So what is the best temperature for growing weed and what about the humidity in your grow room? Check it out!
Cannabis Air & Temperature for Germination
The temperature for germinating cannabis seeds is best at 78° F (25° C) because both low and high temperature impairs germination and growth. The best conditions are native conditions so if you know what type of cannabis that you are growing, you will be able to better match the optimal growing conditions for that variety.
When your seed has sprouted and is growing then your plant is ready for their vegetative growing environment. They will be better able to handle cooler temperature, more intense light, and lower humidity levels.
Be sure to avoid high temperatures and lower intensity of light levels since this will stunt growth and cause very ‘lanky’ formation of the plant.
Necessary Air (Oxygen) for Germination
The last basic necessity for seed germination is air so if a seed is allowed to be in a very moist, soggy growing medium, it will cut off all oxygen supply to the seed.
Another common way seeds get deprived of oxygen is planting them too deep in the medium, this is because the moisture and depth of the seed will cause a lack of oxygen and your seed will not thrive.
Cannabis seeds come provided with enough food within their shell for them to be able to germinate and break through the soil. But, if seeds are planted too deep in the ground, they will not have enough energy for them to be able to break through soil that is too deep.
A good rule of thumb for planting cannabis seeds is to plant them about a quarter of an inch (0.25 inches or 6 mm) deep.
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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.’
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
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.
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.
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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Best Temperature and Humidity for Growing Weed
Getting the temperature right for your cannabis plants is an essential part of each stage of the growing process. If the temperature in your grow room or outdoors is too hot or too cold, your young weed plants will not be able to photosynthesise properly, and this will inevitably affect their growth and development. However, it is not as simple as saying ‘this is the correct temperature; the temperature needs of the plants vary according to their stage of development, so you must have some knowledge of their requirements. To help you, we have written this guide which will explain the best temperature and humidity for growing weed for each phase of your young weed plants.
Now, we understand that establishing the ideal temperature for weed plants can be tricky – some say that it is as much instinct as it is science. However, it is certainly possible to work things out for the growing conditions of your plants, and this article will tell you everything you need to know.
What you need to know about temperature and humidity
The first thing you need to understand is the close relationship between temperature and humidity levels. Let’s look at science. Humidity refers to the amount of water vapour present in the air. At higher temperatures, molecules move at top speeds; thus the probability of condensation of water vapour due to the collision of molecules is less. This makes the air hold more water vapour at high temperatures. In other words, as the temperature increases, the humidity of air also increases.
Most plants including cannabis plants, need humid air to thrive. This is because the pores through which they breathe lose most of their moisture when the surrounding air is dry, a loss that the plant can’t always replace through the water absorbed by its roots. The thinner the leaf – and cannabis plants have quite small, narrow leaves, the higher its need for humidity.
When deciding the correct temperature for your plants, therefore, it is also sensible to assess the humidity levels as the two go hand-in-hand. To do this, you should invest in a good-quality thermometer and a hygrometer, ideally digital models with the ability to store historical maximum and minimum levels.
When the temperature is 68°F (20°C), air can absorb 7.2 ml of water maximum. When this occurs, the air has a relative humidity of 100 percent. There will be so much water vapour that the air will be as dense as a cloud and will affect your ability to see anything. Air with a temperature of 32°F (0°C) is only able to absorb about 5 ml of water. This is the reason why the air is a lot drier in the winter than in the summer.
Temperature and humidity for the germination phase
The first moments of your cannabis plant’s life are crucial. Germinating seeds indoors will allow you to have more control over the temperature, but it is also possible to do so outdoors if the climate conditions allow. Having a high temperature (from 22 to 26°C) is an important factor for your seeds to decide to emerge into the world.
However, the temperature must not fall to less than 20 degrees Celsius nor rise to more than 30. If you are using a greenhouse for the germination phase, be warned that it can get sweltering so you must regularly monitor the temperature. Humidity must also be continuously monitored. If the seed trays dry up, germination will not take place or recently sprouted shoots will wither and die. You must not forget to add water when necessary – a spray dispenser is gentle for this, but you should not give them too much water. The seeds should only be soaking wet during the first two days.
Once the first seedlings emerge with two cotyledons (the first two round leaves that develop), they should be carefully transplanted. If the seeds are autoflowering, you should transplant them to a large pot. If they are feminised seeds, however, you can transplant them to a smaller container and move them to the large bowl when they are a bit more established.
Best temperatures and humidity for the seedling phase
The optimal conditions for cannabis seedlings are a sunny, warm (20-25ºC) and humid environment with well-circulated air. Their underdeveloped root systems mean that seedlings need to be exposed to lots of light and heat. Problems arise as their immaturity means that they cannot withstand high temperatures. Therefore, we recommend that growers maintain 20ºC to 25ºC indoor environments when the lights are on.
Humidity levels also need to be high. Levels between 65 percent and 70 percent are sufficient for seedlings to absorb enough water through their leaves.
Optimal temperatures for the vegetative phase
You can start to relax a bit during the vegetative phase. As cannabis plants mature, they grow stronger and better able to cope with extremes of heat. They start to be more resistant to heat and cold. You can raise the temperature to as much as 30ºC.
As the roots have sufficiently developed to absorb plenty of water, you may wish to reduce humidity levels by 5 percent each week. The relative humidity should ideally fall between 40 percent and 70 percent.
The best humidity and temperatures for the flowering phase
The last phase of the cannabis growth cycle is the flowering phase. Growers should aim to maintain warm temperatures that are pretty much the same as when the plants were at the seedling stage. Ensure that the temperature stays at a nice warm 20ºC to 25C to prevent buds from burning their terpenes. This will allow your plants to produce deliciously potent flowers.
It is also a good idea to lower humidity levels to about 40 percent to 50 percent, especially during the late flowering phase. This encourages the production of highly-prized resin and a higher terpene content leading to a more aromatic and flavourful crop.
Cultivators should be advised that typical temperature variance when the lights are switched off is 5ºC, and this applies to all the phases of development.
Temperatures that are too cold
Temperatures that are too cold will slow down a cannabis plant’s metabolism and its roots system will become increasingly ineffective. If temperatures drop below 12 degrees, the plant is even at risk of death.
The obvious solution to boosting the temperature of the grow room is to get an electric heater and plug it in. This has several disadvantages, however, mainly due to its high consumption of electricity but also because of its drying nature which can affect levels of humidity, and the direct distribution of the heat which makes it hard for all the plants to enjoy the uneven heat. An oil-filled portable radiator is another option if you can get one which isn’t too large to fit into the grow space. We recommend small tubular electric heaters which can be placed conveniently on the floor and only use a few watts of electricity. Radiating cables for indoor use are another excellent alternative, especially if you need to heat trays of seedlings.
Temperatures that are too hot
Reducing heat levels in a grow tent can be much harder to control than the reverse. We recommend using electric fans to circulate the air as much as possible to disperse the heat and thus cool the young cannabis plants.
Placing an exhaust fan in the ceiling vent of your grow tent is also highly effective at reducing heat. After all, heat always rises to the top.
You could also use a cooling humidifier which reduces temperatures while boosting humidity levels. Just take care that the humidity does not increase too much for the growth phase. Remember, seedlings need higher levels of humidity than vegetative marijuana plants, for which 40 percent is optimal.