Thanks for your comment(s). We would be glad to share our sources / bibliography for this or any other article published in Urban Garden Magazine. I can also confirm that no posts from any Internet forums formed any part of our research and they were certainly NOT plagiarized! What do you take us for? LOL! Would it be out of the question that you may have erred into a little self-flattery in this regard?

Notwithstanding your malapropisms and general internet bravado, please consider providing a valid email address with any future posts please, lest we don’t take your outrageous slurs as seriously as we might.

Peace, love and patience,

Everest

Glad to see none of my massages (gojo from TCC) about your plagiarizing of my work are getting posted.

You guys/gals should just have me write your articles for you!

/sarcasm

In situations where CO2 is used there is little point in injecting the CO2 when the stomata are closed – so avoid having an environment where the VPD is high (above 11 millibars (approx.)) during this period. A lowish VPD (between 6-8) will encourage the stomata to open wide and gobble up all that lovely CO2. If you can’t get the VPD down when the lights are on then maybe switch off CO2 injection and save the planet.

During the night period, VPD is not as important because stomata are closed. However, problems can occur when indoor gardens run with a drastically higher VPD during the night in comparison to the day, which could come from using excessive dehumidification during the night. You should aim to have slightly lower VPD in the night than during the day, which is usual for most indoor growers.

If fungal growth is your main concern, running the RH between 55-65% at 70F during the night should be fine. Even running as low as 45% at 70F in the last few weeks should be ok if you want piece of mind when growing varieties that are particularly susceptible to botrytis or mildew. Note that RH can vary from place to place inside the grow area so you may be getting 65% at your RH sensor but without any air stirring going on it could be getting much higher in cooler areas (a cold corner or inside a crowded crop canopy facing a cold wall) where there is not much air movement.

Questions:

Using your chart at 70 degrees should I be able to keep my RH at night time to 55-65% during the last two weeks without fungus problems?

Is the VPD as important during lights out as during daylight?

I am interested in recommendations for the last
two weeks of flowering/fruiting.

Thanks again for the excellent article.

P Dude

The white one is a Centrifugal Humidification System made by Faran, the model number is HR 50. They also do a smaller one called the HR 15. I’m sure if you give it a google you’ll find a few retailers selling them.

The unit further back in black is actually two lots of five disk ultrasonic foggers/misters floating in a shallow reservoir.

I hope that helps

BCMAFF Floriculture Factsheet No.400-5 (June 1994)

Autogrow Systems Ltd – Humidity and VPD

If you are interested in calculating VPD, an on-line calculator can be found here: Autogrow VPD Calculator