Beginners Guide to Relative Humidity

The Vault Cannabis Seed Store Relative Humidity

We know that one of the keys to growing perfect plants is environmental control. No matter what we feed them, how we prune them or how we water them if the environment isn’t conducive to healthy growth we will encounter problems. The primary aspects of the controlled growing environment are humidity and temperature. Plants can be delicate and picky, so we need to ensure their space has the right balance of both. One will affect the other in ways that growers may not foresee, and that is why we have to not just talk about the two aspects of the environment, but bring them together in relative humidity.

Relative Humidity

Whenever we are thinking about humidity in growing terms we are thinking about relative humidity. This isn’t quite the same as the overall humidity of the space, which is essentially the amount of water vapour in the air. However, the amount of airborne moisture does also depend on temperature, hence the term relative humidity. Air will hold different amounts of water at different temperatures. Hot water will add more water and cold air will decrease the moisture.

The reason that humidity is so important is that if plants are too moist or too dry it can cause a whole host of issues. Everything from stunted growth to mould and insects can take down a whole crop if not dealt with properly. Plants also need different levels of heat and humidity in different growing stages. So during the seedling stage, the ideal is 65 – 80% humidity, during vegetation, it’s 55 – 70% and during flowering, it is 40 – 50%.

The same goes for temperature and during the seedling stage, it should sit around 20 – 25c when the lights are on and 18 – 22c when they are off. During vegetation, we move up to 22 – 28c lights on and stay at 18 – 22c with the lights off. Finally, during flowering, we cool off slightly to 22 – 26c lights on and again 18 – 22c lights off.

This of course may vary depending on the type of plant we are trying to grow. Plants from warmer climates will likely prefer higher relative humidity whereas cold weather plants will prefer lower. We always want to attempt to mimic the plant’s natural environment as much as possible.

It is also important to look at the kind of plant we are growing for other reasons. For example plants with dense buds and foliage are far more likely to grow mould in high humidity environments. This is because the air moisture gets trapped in the bud and cannot drain out again. It is not only a good idea to regularly check plants for signs of mould but a hygrometer can let growers keep an eye on the ambient humidity.

Controlling Relative Humidity

Once we know what we are looking for in our growing space we need to figure out how to achieve it.

Monitoring the Relative Humidity:

Of course, it is always a good idea to keep a close eye on the plants and see how they are reacting to their environment. This includes looking out for mould, wilting leaves, silky colouring and a variety of other issues. However, especially for newer growers, it is a good idea to use actual tools to monitor the relative humidity in the space. Buying a decent hygrometer is vital to anyone who isn’t sure about controlling their relative humidity. Honestly, I would recommend them even to the most advanced growers in order to ensure the plants can grow properly.

A few of the top hygrometers on the market are:

  • Thermogrow TP55 – This monitor has a bright and clear to read display that is extremely accurate. It will keep track of any changing humidity and temperature in the space. It is not only easy to read but easy to set up and to use.
  • ACURITE 00613 – This model is cost-effective but still extremely impressive. It is a good option for newer growers as it is reliable and easy to read without breaking the bank. It is also clip and magnet mountable so it can be placed anywhere in the grow space for easy monitoring.
  • RockyMars RT36 – For anyone who has a few grow spaces this portable model can be the best option. Its display is backlit and it has min/max hold capabilities for easy reading.

Increasing Humidity:

  • Simply increase the temperature in the grow space with heaters or by ensuring the space is fully closed off.
  • Reduce the fans in the growing space to lower the air circulation.
  • Before the plants flower, it’s a good idea to use a misting bottle to keep them moist. Don’t do this when flowering as it will likely cause mould issues in the buds.
  • Ensure the surface of the soil remains damp but not wet.
  • Hang wet cloths or towels around the space which will increase the moisture in the room overall.
  • Use larger or warmer lights to bring up the temperature.

Lowering Humidity:

  • Increase the cool air supply with fans, this will reduce the amount of liquid being held in the air.
  • Make sure the plants are being watered at the start of their light cycle, this gives plenty of time in the warmer air for the water to evaporate.
  • Increase the exhaust vent in the grow space or use a dehumidifier. Always make sure a decent amount of money is spent on the dehumidifier as small cheap ones can’t hold very much water.
  • Use low heat lights and potentially fit a cooling tube.
  • Install an airconditioning unit.

By ensuring the relative humidity levels, the combined humidity and heat level, is appropriate we can encourage healthy happy plants. By not paying close attention to relative humidity a grower could quickly lose an entire crop. As always it is important to research for the specific strain we are growing to ensure we can give them what they need. Every plant is different, so we can use these tools to try and figure out the perfect balance.

*Image via Unsplash

Remember: It is illegal to germinate cannabis seeds in many countries including the UK. It is our duty to inform you of this fact and to urge you to obey all of your local laws to the letter. The Vault only ever sells or sends out seeds for souvenir, collection or novelty purposes.

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