Bomb, Bomb Folks!
It’s getting hot and sticky in the garden. What is going on…? Wikipedia says Humidity, is the measurement of the water vapor in the air. What is this water vapor (Humidity), where does it come from, do I want it, and what should I do with it?
We can get super deep on humidity with talks about Absolute Humidity or Relative Humidity (RH). In this article, we are going to keep it simple because we are talking basics.
The indoor garden will be best served by referring to the topic as just humidity.
Fact: the hygrometer we suggest just refers to it as Humidity and spits you out a number between 0-100.
What is humidity or the measurement of water vapor?
Think steam but not super heated. It really is the amount of water in the air.
How can air hold water? Well, don’t think about it too much but it can, and you feel it depending on how much moisture is in the air. Then, when you think you have it figured out, air temperatures play a role in how much moisture can be held in the air. Hot air holds more moisture than cold air.
How did all this moisture get into my grow room?
Well folks, this isn’t rocket science. You watered the plants. Watering your plants brings in 98% of humidity in the grow room.
Recall back to transpiration, the way a plant moves water from its roots to its shoots. Once the water gets to the top, it’s given off into the environment. The moisture will linger in the environment until it’s addressed with an Air Conditioner or a Dehumidifier.
Science has given us a better tool to help plants grow and it is called VPD or Vapor Pressure Deficit. VPD measures the temperature and pressure inside the plant in comparison to the temperature and pressure outside the plant. VPD is a moving value throughout the plant’s life cycle. Generally, vegging and early flowering plants like higher humidity. As the plants ripen, dial back the humidity to prevent mildews and molds. The changing humidity requirements over the plant’s life make it difficult to use on perpetual gardens as compared to a singleton grow where plants are all the same age in flower.
To accurately use VPD, head to the interwebs and Google VPD, you will find a chart. The chart will indicate what humidity should be achieved for the temperature of the room. Again, VPD is for plants of the same age all going through flowering. As plants enter flowering the humidity should be high (like 70%) and weekly dropped by 5% to 40% the last weeks of flowering.
VPD has shown that the closer the internal humidity (pressure) of a plant to its environment will produce the fastest growing and flowering plant. It’s all about moving water (fertilized) from the roots to its shoots. VPD is not ideal for all gardens but all gardens need a certain level of humidity / moisture to encourage growth.
Perpetual gardens, where plants are brought in to the flower room on a cycle prior to the previous plants being harvested, are not ideal for VPD. Since the plants are different ages, late plants do poorly with high humidity (think powdery mildew). Typically, if a garden is run as perpetual, a range of 45-55% humidity is ideal. This gets close to the young plants desire for high humidity and stays low enough to keep PM down during late flowering. The thought may be contrary but both a humidifier and dehumidifier maybe needed in the same room depending on the outdoor season and how dry it is in the garden.
Ideally, most veg rooms are typically more humid than flowering rooms.
In veg, there is no real need to vary the humidity for the plants since they are all going through the same phase. Keep your veg room in a range from 55-65% even upwards of 75% with the right controls.
Regardless of the type of garden you run, keep humidity in mind when the lights shut off at night. The plants have been humming away pumping water and don’t turn off like a light switch. What happens is for about an hour as the plants cool and go to sleep, they are still pumping water into the environment. The result means that daily there is a large humidity spike that needs to be controlled with a dehumidifier. It may be the only hour it runs but could be the difference between success and failure.
Looking back to our oak barrel back in previous articles, these environmental factors all play a role in how fast your plants grow. Your garden will benefit from dialing in every environmental factor to a stable zone.
Tune into the sweet spot!
Air temps 78-82 Deg F, Perpetual grow humidity 45-55% or singleton grow follow VPD.