Humidity Rising? How to Dry Up!
Plants love a high humidity (most of the time). BUT too much of a good thing is bad.
If there’s too much moisture in the air:
- Plants don’t transpire as much
- Nutrient uptake and translocation is slower
- Growth and flowering are stunted
- Bud rot (botrytis) can take hold…especially in flowering
So, you need to make sure your humidity doesn’t climb too high.
The problem is, plants are like little humidifiers - they transpire all the time. This is where they lose water through their leaves.
Unless you remove it, this moisture will increase the humidity in your grow room air. In flowering, when buds have formed, and mould is a threat, this is even more of an issue.
Generally, the best humidity to aim for is:
- 70% - 80% (propagation)
- 50% - 80% (vegetative growth)
- 40% - 60% (flowering)
Is your humidity creeping up? Here’s what to do!
1) Extract Enough Air
This is one of the easiest steps to take. Just remember that extracting more air also impacts your grow room temperature. Some fans make a fair bit of noise at higher speeds, too.
2) Use a Dehumidifier
To remove lots of moisture quickly, grab a dehumidifier.
Save floor space - your humidifier's fixed to the top of your tent.
Move it from room to room – this thing is light and comes on wheels.
How to Size Up
Plants shouldn’t transpire any more water than they’re using. So the amount of water used in 24 hours is what you need to remove.
How much did you fill your reservoir with?
24 hours later, how much is left?
Subtract the amount left from the amount you originally had. That's how much plants have used.
[original amount in tank] - [amount still in tank] = [amount of moisture to remove a day]
If you have a 100L tank, and 24 hours later, it’s 80 litres, plants have used 20 litres. A Quest 70 is ideal.
|Dessicant Dehumidifier||up to 10L per day|
|Quest Overhead 70||up to 26L per day|
|Quest Portable 74||up to 36L per day|
|Quest Portable 114||up to 55L per day|
|Quest Overhead 155||up to 75L per day|
Don’t forget to aim for a lower humidity when it’s cooler.
The cooler your temperature, the lower your humidity needs to be for healthy transpiration.
There’s a handy table here, showing what humidity to aim for, based on your temperature.