Mastering Cannabis Humidity Indoors
Cannabis humidity is a term for the amount of water vapor that is contained in the air for your indoor grow room. It refers to any one of several measurements of humidity.
Formally, humid air is not “moist air” but a mixture of water vapor and other constituents of air so cannabis humidity is defined in terms of the water content of this mixture, called the absolute humidity.
Humidity is, therefore, relative and air holds different quantities of water at different temperatures when you are growing cannabis indoors. The hotter it is then the more moisture air can hold and when the cooler it is there will be less moisture that the air can hold.
The greater temperature variation, the greater the relative humidity variation will be so if you need more cannabis humidity, add a humidifier to your room. If you have a portable air conditioner in your grow room, this will cause the humidity to drop; sometimes it is better to vent the cool air in.
Cannabis seedlings and vegetative plants grow best in 65 – 70 percent relative humidity, while flowering cannabis is best within the ranges of 55-60 percent relative humidity. This is the same as temperature, the more consistent the humidity is, it will promote healthy and evener growth.
When the cannabis humidity is high the water evaporation slows, the plant’s stomata close, and transpiration slows as well as the plant’s growth. If you need to add a heater to the room for the plants.
This will increase the cannabis humidity within the room if there is water that is open to the air. Relative humidity affects the transpiration rate of cannabis’s stomata on the leaves.
Beyond 70 percent relative humidity the pressure outside of the leaf is too high and inside too low, this will cause the plants’ stomata to close up and slows plant growth. A plant that is between 3 – 4 feet tall can easily transpire a gallon of water a day when the humidity is below 50 percent and the same plant will transpire only a half-pint or one-eighth of a gallon on a cooler humid day.
Measuring Relative Humidity
You can measure relative humidity with a hygrometer that you can purchase at most any grow store or hardware store. The hygrometer will give you a reading of the percentage amount of cannabis humidity that is present in the indoor grow room that you place it in.
The humidity should be adjusted to 55 – 60 percent level that is safe and encourages plant transpiration. Relative humidity is an important part of insect and fungus prevention control for indoor gardens.
With humidity above 80 percent, it discourages spider mites but promotes fungus, root rot, and stem rot. When cannabis humidity is below 60 percent it reduces the chances of root and stem rot.
There are several types of hygrometers that are produced, but there are common types of hygrometers are used for indoor grows. There is the spring-type of hygrometers that use a spring, they are relatively inexpensive and accurate within 5 – 10 percent.
Another type of hygrometer is the psychrometer, this one uses a dry bulb and a wet bulb, it is a little more expensive but very accurate. One of the last hygrometers that cannabis growers love to use is digital hygrometers that are very accurate and affordable.
A humidistat is like a thermostat where it regulates humidity instead of temperature; many houses have these built into them. With newer environmental control systems for your garden, you can plug in your heater, humidifier, air conditioner, fans and CO2 system all up to a single control.
When the cannabis humidity gets too high or too low, it will kick on whichever equipment is needed to get the environment back into balance. Humidity lowers when heat is present, in a grow room the HID lamp and ballast radiates heat and it helps to keep the humidity about right within a grow room.
If there are additional heat sources such as a wood stove or gas heater, this will lower humidity too much and should be watched. If dry hot heat is blown directly onto plants, it will cause them to quickly dehydrate.
You can increase the cannabis humidity in your room by misting the air with water or leave a bucket of water in the room to evaporate into the air. Or you can purchase a humidifier that works well within the room, but a humidifier will some extra work since it will need to be replenished with water every couple of days.
On the other hand, if your ventilation system is unable to lower humidity in your room then a dehumidifier can assist in lowering it to the proper levels. Also, air conditioners draw moisture from the air and lower the humidity, which works well.
In most cases, if the humidity is high, you will need to empty the water bucket under the air conditioner so it does not overflow into the room. When you are rooting clones or seeds they thrive best in 70 – 100 percent humidity.
In most cases, marijuana growers will use humidity domes to contain the humidity that is controlled by adjustable vents on the top or sides of the dome.
If seeds or clones are allowed to be in a dry environment or environments that are under 70 percent, they will not be able to absorb enough water with their under-developed roots so they will quickly die.
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