Opinions on RH during flower

Greetings RIU, I am in the middle of week 5 of flower (8-10 week strain from what I've read) and have been adjusting my RH per a vapor pressure deficit chart I found online and so far everything seems to be going well. Hoping to get some opinions on when I should lower the RH to avoid mold/bud rot and perhaps increase trich production. Also what RH should I be lowering it to? I keep my temps around low 70s during lights on and high 60s lights off if it matters.
Thanks!

I've never seen mould indoor myself and sometimes fight to keep RH below 60% lights off. My area is bad for PM though and if I can keep RH below 50% it doesn't show up, anything above that and I'll see it on strains that have little or no resistance to it, even with preventative spraying on some strains, particularly Indica's.

Only relevance temps have is higher temps = lower RH, based on the temps you posted, you have room for some additional heat in there which should reduce your RH further.

I would try to make sure the humidity doesn't stay above 60%. I have heard of some people going as 30% in the last few weeks of flowering.

I go low as possible...because the way I was taught, to create some more resin

Nice do you give it total darkness for a day or two before harvest? I heard that forces the plant to produce more trichromes as well. I would think with 20% RH coupled with the total darkness could yield super frosty buds. What do you think?

My property is so dry it's been under 20% for the last 3 months straight never see mold again

peter berger said:

Nice do you give it total darkness for a day or two before harvest? I heard that forces the plant to produce more trichromes as well. I would think with 20% RH coupled with the total darkness could yield super frosty buds. What do you think?

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supplementing with UV-B also gives you more trichs. plant will produce more as a sunscreen from the UV.

good air circulation is always crucial to avoid mold too. i don't adjust RH at all throughout my grows. it is usually low here in CO especially at close to 9000 ft.

@nomoresnow : i'd change your temp range too for flower. you want a good 10 to 15 degree diff b/t lights on and off. i think your range is too close together.

rkymtnman said:

@nomoresnow : i'd change your temp range too for flower. you want a good 10 to 15 degree diff b/t lights on and off. i think your range is too close together.

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I can't get much spread because of my ac unit, it's just set to a certain temp and whatever heat my light puts out brings the temp up.

I had 2 fans blowing on them but turned one off cuz I thought it was beating them up too much. I still get a little bit of movement out of all the plants so I think it's ok. I'll turn down the ac so it always stays above 70° and turn the dehumidifier down a bit.
Should I drop the rh as far as it will go now or wait until I am closer to harvest? I'm thinking I have 4 or 5 weeks left but it's my first grow so only guessing.

I'm not a rh professional by any means but what I've learned from experience is having low humidity has never done me wrong and high humidity has screwed me up the ars... Just my $.02

nomoresnow said:

I can't get much spread because of my ac unit, it's just set to a certain temp and whatever heat my light puts out brings the temp up.

I had 2 fans blowing on them but turned one off cuz I thought it was beating them up too much. I still get a little bit of movement out of all the plants so I think it's ok. I'll turn down the ac so it always stays above 70° and turn the dehumidifier down a bit.
Should I drop the rh as far as it will go now or wait until I am closer to harvest? I'm thinking I have 4 or 5 weeks left but it's my first grow so only guessing.

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i'd play around with the A/C and see if you can get a bigger difference in temps.

the rule of thumb i went by for RH was above 60 for veg and below 40 for flower.
strong air flow won't affect the plants other than strenghtening the stems which will help when those buds get huge.

i'd get your RH around 30 to 40 if possible fore the rest of the grow

good pt ca mtn man. you get mold and your harvest is in the trash. the plant will adapt to lower RH's without issue.

I grow in my danky musty damp old city basement. I'm very susceptible to mold so I have to keep an eye on it when flowering. If I let it get above 50% for me thats asking for trouble. Strains also have a lot to do with it as some are very resistant to it more than others. Lots of air movement and a carbon filter fan help a lot.

If you use co2 it helps with mold. Dr. Who gave me this advice.

That chart is similar to the one I have. I don't use co2, just an in wall ac unit, a 4" inline fan that pipes in outside air, a 70ppd dehumidifier and a couple oscillating fans in a 4.5'x4'x8' room.... with 4 plants in 5gal pots it's packed in there. I bumped my temps up to 75-70 and turned the dehumidifier down so now my gauge at canopy level in the middle of the plants is reading 38%-42%. I raised it up about an inch from where it was in the pic because the rh readings were jumping all over, I think it was picking up all the moisture coming out of the leaves.

On a side note, I accidentally touched one of the smaller buds while I was adjusting the dehumidifier and my fingers were practically stuck together and smelled like juicy fruit gum and pine, so excited!

ax 1000000 on the VDP chart. I run 75% in veg (82*) and 65% r/h (73-75*) in flower. I use an ultrasonic fogger system in my veg room. I can dial in the r/h by fan speed or my timer.