In the US there are 26% of the whole population has at least smoked weed once, and with the rise in popularity and weed research, that number is only going to rise.

So, maybe you want to get into this giant industry that is being legalized everywhere in the world day after day.

In this article, we will go over why temperature and humidity are important for your weed growing. It doesn’t matter if you are growing it for yourself; you should always aim for the best quality.

How Temperature and Humidity Levels Interact?

It’s of crucial matter that you know that temperature and humidity levels are closely related to one another. When we say humidity in this context it means relative humidity or RH. The relative humidity is the ratio of the partial pressure of water vapor to the maximum vapor pressure at the same temperature.

You get the whole concept when you know the basic principle that warm air holds more water than cold air. So, in your grow room, you need to extract warm air and allow cool air to enter the room.

Humidity Levels and Temperatures: From Seeding to Harvest

You need to know exactly what you should be aiming for when it comes to humidity and temperatures for growing quality cannabis. For this, we are going to divide the life of a cannabis plant into 4 different stages where for each one, there is a different setting for temperature and humidity to ensure healthy growth. 

When it’s time for harvesting, whether you plan on drying your buds or keeping them fresh to make rosin, you want to lower the humidity level in your grow room. This helps prevent mold and other diseases that can ruin your harvest. The ideal temperature range for harvesting is between 20°C and 23°C (68°F – 73°F) with a relative humidity of 45% to 55%.

Equipment-wise, there are only two things that we need to have for these parameters: a hygrometer and a thermometer. You should have a few of them in case some don’t work; you can check the others.

In the list below, we are going to cover recommended humidity levels, reasons for that humidity, and temperatures with and without the light on:

Seeding Stage

  • Humidity levels should be in the range of 65 to 70%.
  • Reason: The root system is not yet established.
  • High humidity levels allow water intake through leaves.
  • Temperature with the lights on should be from 20 to 25C° and when the lights are off it should be 4 to 5C° lower.

Vegetation Period

  • Humidity levels can and should be lowered by 5% each week and be in the range of 40 to 70%.
  • Reason: There are roots now that absorb more water and evaporation through leaves cool down the plant.
  • Temperature can be increased due to leaves cooling the plant but it’s not necessary. 
  • Temperature with the lights on should be in the range of 22-28C° and 4-5C° lower when lights are off.

Flowering Period

  • Humidity levels need to be lowered to 40-50%, which becomes extremely important in this stage. Anything above 60% is going to be very bad.
  • It’s best to lower temperatures in the flowering period.
  • The temperature with the lights on should be 20-26C°, and there are no more lights off. You should avoid high temperatures in this period.

Late Flowering

This is about one to two weeks before harvesting, these steps are not necessary for the process but can improve flavor, yield, and appearance.

  • Humidity should be as low as possible around 30-40%
  • Lower temperatures and an increase in temperature difference between day and night
  • Temperatures with lights on should be around 18-24C° and with lights off it should go to minus 5-10C°.

Adjusting Temperature and Relative Humidity

Now that we know what ranges of humidity and temperatures we need to aim for it’s time to get to the practical part. We need to go over ways to control things and bring them back to balance when they are not within our ranges.

Most of the people who are growing weed are going to have a hard time keeping both humidity and temperature in check at all times. Especially if you are living somewhere that is either very hot or very cold.

So, in the list below, we are going to explain how to keep both parameters in check at all times:

1. How to Lower Humidity

  • Run your tube vent at a higher velocity or upgrade it.
  • Increase cool/fresh air supply.
  • Try to water your plants right after the lights are switched on.
  • Invest your money into a decent-sized dehumidifier.

2. How to Lower Temperatures

  • Install air conditioning; they can also lower humidity in the room.
  • If you are growing with HPS lights, consider using a cool tube.
  • Like with lowering humidity, you should extract warm air and let in more cool/fresh air.
  • You should turn off lights during the daytime and always turn them on at night.

3. How to Raise Humidity

  • You should always keep the surface of the soil moist but not wet.
  • You can increase humidity levels with a spray bottle but that won’t last for long.
  • Hanging wet towels and clothes and putting open water containers in grow room can be a great way to raise humidity.
  • It’s also advisable to invest in a humidifier with a large water tank, so you don’t have to refill it as often.

4. How to Raise Temperatures

  • Place a heating mat in your grow room.
  • Isolate your grow room.
  • Use a space heater but remember it needs to have a thermostat.
  • You can also simply upgrade to a bigger grow light with more heat.

Closing Thoughts 

Whether for personal or commercial use, humidity levels and temperature play an important role in growing cannabis. By closely monitoring and controlling the temperature and humidity levels, you can ensure you have quality marijuana.

We are sure that after reading this article, you will be equipped with the right knowledge to start growing healthy cannabis plants.



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