What is the ideal humidity level for Growing Cannabis?
Humidity is an important topic for cannabis growers. But why is humidity so important for cannabis plants, and what are the ideal humidity levels to maintain in your grow room?
To better understand why humidity is important to plants, it helps to think about how plants absorb air from the environment. Remember, all plants respire carbon dioxide from the environment through their leaves. In doing so, they naturally lose some of the water retained in their foliage.
Dry air causes plants to lose more water when respiring than moist air, and hence, drives down the overall moisture content in the plant more quickly. Once the environment becomes too dry, plants lose more water than they are able to regain via their roots.
When this happens, plants will almost entirely close the pores in their leaves in order to minimize moisture loss. This works, of course, but also means the plants receive less carbon dioxide from the environment. This causes cell death within the plants and leaves them looking limp and ill.
Now, you might think to water your plants more regularly in order to combat moisture loss in dry conditions. And while it seems logical, it won’t work. As you overwater the soil, you’ll only reduce the amount of air in the soil, further asphyxiating the plant and also increasing the chances of the plants developing root rot.
When plants have the right amount of humidity, however, they flourish. The correct amount allows plants to open their pores more fully, respire more carbon dioxide, and grow rapidly.
However, overly moist conditions can also be harmful to plants, especially cannabis, and puts them at risk of developing bud rot and other diseases as water builds up in the thick foliage and creates the perfect environment for bacteria and fungi.
HUMIDITY LEVELS AND TEMPERATURES: FROM SEEDLING TO HARVEST
We need to define what humidity and temperature control actually means when growing cannabis. It makes sense to divide the life of cannabis plants into 4 different stages in which humidity levels, and temperatures, should be adjusted to ensure healthy growth. Don’t think that humidity and temperature control is complicated and not worth it! It’s generally very easy, and more about keeping parameters within a certain range, and as constant as possible.
The first thing you need to do is to buy a hygrometer and thermometer, preferably a digital one with memory function, also showing maximum and minimum values of the past. Some hygrometers aren't the most accurate, so don’t bother having several devices in your grow room to compare values. Now that we’re able to closely monitor our conditions, we can get to the essence of humidity and temperature control – the actual humidity levels and temperatures we aim for.
1. Seedling Stage
Optimal Humidity is 70% RH
A new cannabis clone showing her first roots. Clones need time to develop a root system to intake water. Young clones are solely dependent on getting water through their leaves from the air and this is only possible with high humidity.
Maintaining high levels of humidity will dramatically increase the chances of clones rooting successfully, and will increase young clone growth.
This is why many growers use a humidity dome for new clones!
2. Vegetation Period
In this stage the RH can be 50-80%
Now that your plants have entered their main growing phase the RH can be a lot more varied. This is because your plant will now have a much bigger surface area with which to transpire, meaning less stress is put on it through faster transpiration.
However, this does mean your plants can transpire at a much greater rate, be sure to keep an eye on your plants. If the levels of humidity drops below a safe level then your plants will transpire so rapidly that they run the risk of over fertilization from their fast uptake of nutrients drawn in from the soil.
3. Flowering Period
The final growth period of the weed plant is the flowering stage, which is where all of the buds, the THC, and those crystal trichomes develop. You will once again need to make some changes in terms of humidity and temperature for the weed plant flowering stage. Here, you want to keep humidity fairly low.
The plants can handle it, they don’t need the air to be too humid, and it can actually cause problems. A humidity level between 35% and 40% for the flowering stage will do just fine. Now, when it comes to temperature, for the flowering stage, you want to turn it down a bit when compared to the vegetative state.
4. Late flowering (1-2 weeks before harvest)
Bring down humidity levels as much as you can: 30-40%
Lower daytime temperatures, and also increase the temperature difference (day/night)
How to lower humidity levels in grow rooms?
If you grow marijuana in too humid conditions you risk mold, mildew, and other problems. It’s fairly easy to lower moderately high humidity issues.
Proper ventilation will help replace humid grow room air with fresh air, which can lower humidity while bringing in fresh supplies of CO2. Make sure to have lots of air movement blowing on the plants directly, this reduces the chances of problems from humidity issues such as bud rot, mold, or mildew.
Using a dehumidifier can reduce indoor grow tent air moisture content quickly. Dehumidifiers for cannabis can be attached to humidity sensors to keep your room with in a desired range.
Air conditioners cool air by removing moisture, making them another good way to reduce not only humidity levels but heat levels as well.
Defoliating your marijuana plants can help reduce the amount of large fan leaves the often touch each other and lead to moisture issues. Since these fan leaves release moisture in the air, taking some out will help reduce this. But don’t go nuts and chop away your fan leaves unless you’re sure what you’re doing, removing these leaves will deprive the plant of energy sources.
How to raise humidity levels in grow rooms?
Humidifier for Plants – will add additional moisture to the air, I like the evaporative type of humidifier because it also works to cool down temps slightly. Make sure you get a humidifier with a large holding tank (holds at least 6 gallons of water at a time). Those “one-room” humdifiers with a 1.5 gallon tank often need to be refilled several times a day.
This humidifier for cannabis is an evaporative swamp cooler that holds 7 gallons of water at a time – great for hot, dry climates.
Swamp cooler – will cool down air while increasing the relative humidity; works best when humidity is too low and temperature is too high. Read how one user used a swamp cooler to control his humidity.
To better understand why humidity is important to plants, it helps to think about how plants absorb air from the environment. Remember, all plants respire carbon dioxide from the environment through their leaves. In doing so, they naturally lose some of the water retained in their foliage.
Dry air causes plants to lose more water when respiring than moist air, and hence, drives down the overall moisture content in the plant more quickly. Once the environment becomes too dry, plants lose more water than they are able to regain via their roots.
When this happens, plants will almost entirely close the pores in their leaves in order to minimize moisture loss. This works, of course, but also means the plants receive less carbon dioxide from the environment. This causes cell death within the plants and leaves them looking limp and ill.
Now, you might think to water your plants more regularly in order to combat moisture loss in dry conditions. And while it seems logical, it won’t work. As you overwater the soil, you’ll only reduce the amount of air in the soil, further asphyxiating the plant and also increasing the chances of the plants developing root rot.
When plants have the right amount of humidity, however, they flourish. The correct amount allows plants to open their pores more fully, respire more carbon dioxide, and grow rapidly.
However, overly moist conditions can also be harmful to plants, especially cannabis, and puts them at risk of developing bud rot and other diseases as water builds up in the thick foliage and creates the perfect environment for bacteria and fungi.
HUMIDITY LEVELS AND TEMPERATURES: FROM SEEDLING TO HARVEST
We need to define what humidity and temperature control actually means when growing cannabis. It makes sense to divide the life of cannabis plants into 4 different stages in which humidity levels, and temperatures, should be adjusted to ensure healthy growth. Don’t think that humidity and temperature control is complicated and not worth it! It’s generally very easy, and more about keeping parameters within a certain range, and as constant as possible.
The first thing you need to do is to buy a hygrometer and thermometer, preferably a digital one with memory function, also showing maximum and minimum values of the past. Some hygrometers aren't the most accurate, so don’t bother having several devices in your grow room to compare values. Now that we’re able to closely monitor our conditions, we can get to the essence of humidity and temperature control – the actual humidity levels and temperatures we aim for.
1. Seedling Stage
Optimal Humidity is 70% RH
A new cannabis clone showing her first roots. Clones need time to develop a root system to intake water. Young clones are solely dependent on getting water through their leaves from the air and this is only possible with high humidity.
Maintaining high levels of humidity will dramatically increase the chances of clones rooting successfully, and will increase young clone growth.
This is why many growers use a humidity dome for new clones!
2. Vegetation Period
In this stage the RH can be 50-80%
Now that your plants have entered their main growing phase the RH can be a lot more varied. This is because your plant will now have a much bigger surface area with which to transpire, meaning less stress is put on it through faster transpiration.
However, this does mean your plants can transpire at a much greater rate, be sure to keep an eye on your plants. If the levels of humidity drops below a safe level then your plants will transpire so rapidly that they run the risk of over fertilization from their fast uptake of nutrients drawn in from the soil.
3. Flowering Period
The final growth period of the weed plant is the flowering stage, which is where all of the buds, the THC, and those crystal trichomes develop. You will once again need to make some changes in terms of humidity and temperature for the weed plant flowering stage. Here, you want to keep humidity fairly low.
The plants can handle it, they don’t need the air to be too humid, and it can actually cause problems. A humidity level between 35% and 40% for the flowering stage will do just fine. Now, when it comes to temperature, for the flowering stage, you want to turn it down a bit when compared to the vegetative state.
4. Late flowering (1-2 weeks before harvest)
Bring down humidity levels as much as you can: 30-40%
Lower daytime temperatures, and also increase the temperature difference (day/night)
How to lower humidity levels in grow rooms?
If you grow marijuana in too humid conditions you risk mold, mildew, and other problems. It’s fairly easy to lower moderately high humidity issues.
Proper ventilation will help replace humid grow room air with fresh air, which can lower humidity while bringing in fresh supplies of CO2. Make sure to have lots of air movement blowing on the plants directly, this reduces the chances of problems from humidity issues such as bud rot, mold, or mildew.
Using a dehumidifier can reduce indoor grow tent air moisture content quickly. Dehumidifiers for cannabis can be attached to humidity sensors to keep your room with in a desired range.
Air conditioners cool air by removing moisture, making them another good way to reduce not only humidity levels but heat levels as well.
Defoliating your marijuana plants can help reduce the amount of large fan leaves the often touch each other and lead to moisture issues. Since these fan leaves release moisture in the air, taking some out will help reduce this. But don’t go nuts and chop away your fan leaves unless you’re sure what you’re doing, removing these leaves will deprive the plant of energy sources.
How to raise humidity levels in grow rooms?
Humidifier for Plants – will add additional moisture to the air, I like the evaporative type of humidifier because it also works to cool down temps slightly. Make sure you get a humidifier with a large holding tank (holds at least 6 gallons of water at a time). Those “one-room” humdifiers with a 1.5 gallon tank often need to be refilled several times a day.
This humidifier for cannabis is an evaporative swamp cooler that holds 7 gallons of water at a time – great for hot, dry climates.
Swamp cooler – will cool down air while increasing the relative humidity; works best when humidity is too low and temperature is too high. Read how one user used a swamp cooler to control his humidity.
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