Humidifier/Echaust question

I try for best the best vpd the conditions allow sometimes its ideal other times its well out.

the uk isn't great for growing its cold and rarely below 90% rh, surprisingly rot isn't a big problem I think the humidity tale has been blown way out of proportion, humidity is conductive to mould no doubts but live plants aren't, with good air flow 90% healthy plants will take mould spores in their stride.
Folk in low humidity areas of the world still have bud rot issues if the plants aren't healthy, I'm not trying to promote high humidity lol I'm saying chill 60/70% isn't too concerning to healthy plants.

If you plug in leaf temps +2-3 degree you pretty much get what ive been recommended by growbro/growshop dudes for HPS growing for years.
Without that radiant heat the vpd recs look very different and scary to someone used to hps grows, it looks very mold inducing. But with good air flow this doesnt seem to happen. I can understand someone in a tent being scared of those high rh but it really isnt much more difficult than moving air above and below cannopy, and lolipopping anything to deep down, something you should anyway really. If you cant keep a match lit in any part of your grow space, you eont get mold unless you introduce it by carelessness intracting from a moldy place or if youve gotten mold spores in you led heatsinks that you cant clean.
VPD doesnt grow great weed, it increases transpiration. You can run vpd at the lower range of transpiration if you compensate by raising nute levels; less volume of a stronger juice. In any case its more of a guideline, showing where to take your environment when you have transpiration related issues. See slouchy plants; check which way to go with vpd.

Well, somehow I didn’t notice all the replies to my thread. Thank you

Star Dog said:

I try for best the best vpd the conditions allow sometimes its ideal other times its well out.
View attachment 5437238
the uk isn't great for growing its cold and rarely below 90% rh, surprisingly rot isn't a big problem I think the humidity tale has been blown way out of proportion, humidity is conductive to mould no doubts but live plants aren't, with good air flow 90% healthy plants will take mould spores in their stride.
Folk in low humidity areas of the world still have bud rot issues if the plants aren't healthy, I'm not trying to promote high humidity lol I'm saying chill 60/70% isn't too concerning to healthy plants.

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I’ve read several people state that they grow in 70s humidity through flower and with good airflow they never have bud rot. Either way I decided to raise the airflow and vpd as I watered them all really good yesterday and gave them some excellent worm castings with live worms inside from uncle Jim’s worm farm. Scratched in some espoma garden tones about 2 teaspoons a plant (1tsp for the little ones in 2 gallon). The other big plants are in 3 gallons. One thing I’m noticing is I believe the small veg tent is in need of some fresh air, so I’m gonna go and put a small exhaust fan on it. May end up buying another drum fan to move the air around in this room.

Rocket Soul said:

Yo always need exhaust or humidity will slowly rise to 100% or close to it. I guess if you open every once in a while the tent but really some exhaust is necessary.
You can try extracting from the bottom and intracting from the top; this will keep the tent more hot and moist

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Yes I’m noticing with my small grow tent that the plants are drooping and don’t look as lively because the airflow is not as good in there. I lm sure the stagnant air is doing them good

Rocket Soul said:

If you plug in leaf temps +2-3 degree you pretty much get what ive been recommended by growbro/growshop dudes for HPS growing for years.
Without that radiant heat the vpd recs look very different and scary to someone used to hps grows, it looks very mold inducing. But with good air flow this doesnt seem to happen. I can understand someone in a tent being scared of those high rh but it really isnt much more difficult than moving air above and below cannopy, and lolipopping anything to deep down, something you should anyway really. If you cant keep a match lit in any part of your grow space, you eont get mold unless you introduce it by carelessness intracting from a moldy place or if youve gotten mold spores in you led heatsinks that you cant clean.
VPD doesnt grow great weed, it increases transpiration. You can run vpd at the lower range of transpiration if you compensate by raising nute levels; less volume of a stronger juice. In any case its more of a guideline, showing where to take your environment when you have transpiration related issues. See slouchy plants; check which way to go with vpd.

Click to expand...

I really am scared of mold so I took heed to what others warned me and did raise the vpd for my plants that are still early in flower this month. It’s sitting around 68rh and 84f in my 2x4. Plants must be around 20 days in

Avering said:

Well, somehow I didn’t notice all the replies to my thread. Thank you

I’ve read several people state that they grow in 70s humidity through flower and with good airflow they never have bud rot. Either way I decided to raise the airflow and vpd as I watered them all really good yesterday and gave them some excellent worm castings with live worms inside from uncle Jim’s worm farm. Scratched in some espoma garden tones about 2 teaspoons a plant (1tsp for the little ones in 2 gallon). The other big plants are in 3 gallons. One thing I’m noticing is I believe the small veg tent is in need of some fresh air, so I’m gonna go and put a small exhaust fan on it. May end up buying another drum fan to move the air around in this room.

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The key issue for bud rot is temperature. When temps fall <75, that's favorable for botrytis.

Another way to reduce the chances for bud rot is to use a silica supplement. The addition of silica improves the strength of cells and will tend to stave off mold and mildew.

Rocket Soul said:

If you plug in leaf temps +2-3 degree you pretty much get what ive been recommended by growbro/growshop dudes for HPS growing for years.
Without that radiant heat the vpd recs look very different and scary to someone used to hps grows, it looks very mold inducing. But with good air flow this doesnt seem to happen. I can understand someone in a tent being scared of those high rh but it really isnt much more difficult than moving air above and below cannopy, and lolipopping anything to deep down, something you should anyway really. If you cant keep a match lit in any part of your grow space, you eont get mold unless you introduce it by carelessness intracting from a moldy place or if youve gotten mold spores in you led heatsinks that you cant clean.
VPD doesnt grow great weed, it increases transpiration. You can run vpd at the lower range of transpiration if you compensate by raising nute levels; less volume of a stronger juice. In any case its more of a guideline, showing where to take your environment when you have transpiration related issues. See slouchy plants; check which way to go with vpd.

Click to expand...

Amen!

It's amazing to see the amount of mishegas about VPD. It's not just here on RIU. I frequent another cannabis site and people get completely twisted around the axle there, as well.

VPD is not the Holy Grail. It's just a way of combining temperature and RH to help plants grow well. If VPD is 1 or so and 1.2 or higher in flower, you're going to do fine. As you point out, as temperature increases and/or RH drops, plants have to transpire more. If temperature is really high and/or RH is really low, transpiration can get so high that lots of nutes get taken up and nutrient issues will show up.

Everyone running around with their hair on fire will not that I wrote "temperature increases and/or RH drops". Well, "VPD" is just an easier way to put and sure as heck is easier to use with a controller device.

When growers have nutrient issues, check that they've mixed the nutes correctly (I f'd up 28 gallons of nutes yesterday but caught it before I swapped the res, so yeh, dumbshit happens) and if they're watering correctly. If both of those are being done right, check the temp and RH and it's amazing how often those two parts of the grow environment are out of whack. A little hot and dry or a little cold and wet aren't a big issue. But when growers are running EC 2.5 with 45% RH and 85°, things aren't going to work out well.

VPD doesn't have anything to do with that condition. It's too hot and dry or, in some cases, cold and wet, and the nute strength needs to be adjusted.

And the idea that it's only something that works in a laboratory - that's true only if the laws of physics don't apply to cannabis plants.

Avering said:

I really am scared of mold so I took heed to what others warned me and did raise the vpd for my plants that are still early in flower this month. It’s sitting around 68rh and 84f in my 2x4. Plants must be around 20 days in

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This is from Mitch Westmoreland's super videos on cannabis cultivation. He's a PhD student studying under Bugbee and he released a video about a year ago (title in the screenshot) in which he discusses four major topics re. cannabis, on of which is temperature.

The graphic below is from his recent video but he also did a video in 2021 that discusses cannabanoid levels and temps in flower. Bottom line - if the temperature at the tops of flowers is in the 80's, your cannabinoid levels will plummet.

I've generally grow with ambient temps in the low 80's in flower but I've had to re-think things after this research.

The 78° mark is the highest it should be. Some cultivars should be kept cooler.

Check out the video. It's excellent.