VPD in flowering

[Timj]

I find this chart helpful. You can plug in your values to quickly check your VDP. I don't get crazy controlling mine and always have very respectable harvests. https://vpdchart.com/#F,53,76.1,72.5

 

[Douglas.Curtis]

Wow, that is really unlucky a NLD molding at 55%. I've run Afghanicas with consistent 65-70% RH and no fungi problem indoors (as long as you have adequate ventilation and defoliate). I guess big dense buds are a liability no matter the genotype.

Nutrition, nutrition, nutrition.

As for myself, I prefer a VPD which is muuuch higher than most charts show. 70F max and mid 20's - low 30's RH. Veg to size before flip, because you're not going to get explosive flower growth. What you do get is an insane resin to plant ratio.

 

[Crooked8]

Hey bud.

My newest unit is 14 years, and I dread to think how old my oldest is. It's loosing some efficiency now, but uses a proper blower fan and buckets out 13c air, when it's about 25c going in. I have to plumb in the drain, as it's trickling more than dripping at times. It uses just the same parts as a fixed install, so there should be no difference in reliability. Just like your domestic fridge or freezer, they should really last till they rust away.

The cold bit shouldn't be getting below freezing, with enough air over it. Though the wider fin spacing of a freezer will always be more resistant to freezing than the closer spacing of a chiller. These are things the manufacturer should be taking care of though.

My fridge man won't even look at a portable unit. He wants to tell me they are different, but fails at a weak jaw movement. He knows I changed out all the mechanical controls on our walk-ins, to programmable stuff with digital displays. Controllers I jog along for him when he doesn't want to wait for the cycle time. So when I tell him it's the same, he just chews air. Our main aging problem there, is the acidic nature of food stuffs, eating the evaporator over time. He want hear of leak seal. Again, he's chewing air, with no words coming out. He was hard to find though, so we let the old gizzard get on with it.

I have to wonder.. is the resin in the air going to eat away at the alloy or copper cores. All them voc's that we actively try to get more of. My units don't get used in sealed rooms, where that risk exists. Like the OP, I treat the air going in.

You know.. that might be it. Years ago we knew of a guy changing quite a few dehu's on a yearly basis. They were always caked up, and a disposal problem. I had clean forgot about this, as it was an isolated case for me. Strongest tested weed ever found in the UK, when they got it. I just heard the story, as I was asked why it might be happening. I was clueless.. It must be 30 years ago.

Dude, my duuuuude, i agree maybe its air quality impacting efficiency and longevity here. Having run many non commercial ac and dehums, they were effed up in no time. Ive run through SO many. Meanwhile, current me is running commecial level AC and quest dehums cranking no problem. BUT, a big but, i have to change filters literally every month on them all. I mean i set it in my calendar to do so. Its so dramatic. 2in badass merv 10+ filters on the quests get swapped and totally change color every 30 days. I do the same for my AC blower which is a carrier, imo the best there is. I do not recommend a high Merv or tight filter for those. Looser and more efficient air movement is the way here ime. As always i love your insight my dude. You gotta come to California and puff down w me some day lol.

 

[Crooked8]

I find this chart helpful. You can plug in your values to quickly check your VDP. I don't get crazy controlling mine and always have very respectable harvests. https://vpdchart.com/#F,53,76.1,72.5

There are really convenient apps for this too. But check it, not all are the same! You can plug values into some and get BS results. I recommend the Dr. greenhouse VPD app here. Makes the most sense. Tells you when you are in the goal range and in danger of stress etc.

 

[Crooked8]

Nutrition, nutrition, nutrition.

As for myself, I prefer a VPD which is muuuch higher than most charts show. 70F max and mid 20's - low 30's RH. Veg to size before flip, because you're not going to get explosive flower growth. What you do get is an insane resin to plant ratio.

My dude, 20-30% RH and you are severely strangling your plants ability to transpire. Resin or not, no reason to do so weeks 1-6, at all. Your VPD must be so friggin high. I admire your effort to push your plants but dauym, thats way too hard imo. If you give them an easier time earlier on it will repay you in spades. It doesnt matter what youre feeding if they can barely even use it.

 

[thugpoet]

Nutrition, nutrition, nutrition.

As for myself, I prefer a VPD which is muuuch higher than most charts show. 70F max and mid 20's - low 30's RH. Veg to size before flip, because you're not going to get explosive flower growth. What you do get is an insane resin to plant ratio.

I have had 2 times spider mites in different setups (including one time where I had lots of ventilation, reasonable temps and a humidifier the whole cycle). So anything below 40s seems like tempting fate to me.
It's worth noting that at <70F 25-30% RH the plants will have a much slower metabolism, slower growth, yield and possibly slightly longer flowering times. It's definitely something that not everyone is ready to sacrifice.

Interesting that you mention that, it is possible to induce or simulate acute hydric stress in late flower to stimulate the production of resins, but there is virtually no point in doing this before flower onset from my understanding. Veg needs a lower VPD for sure.

Cannamicably,

Thug

 

[Douglas.Curtis]

My dude, 20-30% RH and you are severely strangling your plants ability to transpire. Resin or not, no reason to do so weeks 1-6, at all. Your VPD must be so friggin high. I admire your effort to push your plants but dauym, thats way too hard imo. If you give them an easier time earlier on it will repay you in spades. It doesnt matter what youre feeding if they can barely even use it.

I live in the desert. Without spending a LOT of cash, cooling the dry air is as good as it gets. FWIW, I feed very lightly due to these high transpiration rates and it works well. They definitely use a LOT of water.

 

[WingzHauser]

Is that why a lower RH is suggested for flower?

No one knows. The theory is flawed, in that chelated nutes will flow against transpiration in reality, and that PK relies on diffusion for uptake, not transpiration. 99% of Cannabis info is misinfo. Look at what people are doing these days. Fine tune vpd with imaginary arbitrary numbers, then dim lights to deal with real issues. Something tells me they miss the point of growing plants following all this bro grower weed dude info.

Some say a low rh is recommended for mold. So I tested that. I grew plants with no fan except a moldy wicking humidifier. Dripping water leaves stuck together the entire grow never dropped below 80% rh or 90°. The bud was great. Meanwhile all my peers point to curled leaves as heat stress in their 70 degree tent and blame mold on 65% rh.

I live in the desert. Without spending a LOT of cash, cooling the dry air is as good as it gets. FWIW, I feed very lightly due to these high transpiration rates and it works well. They definitely use a LOT of water.

You must exhaust outdoors. Otherwise plants become their own humidifier. I've started breeding arid varietals, so far the ones that tolerate zero humidity are very dank.

 

[Crooked8]

I live in the desert. Without spending a LOT of cash, cooling the dry air is as good as it gets. FWIW, I feed very lightly due to these high transpiration rates and it works well. They definitely use a LOT of water.

Gotta work with what we got! Respect

 

[Ca++]

I live in the desert. Without spending a LOT of cash, cooling the dry air is as good as it gets.

Have you used evaporative coolers? It's very cheap cooling, but is unpopular as it raises RH. I'm not sure that's an issue for you though.

 

[flylowgethigh]

I live in the desert. Without spending a LOT of cash, cooling the dry air is as good as it gets. FWIW, I feed very lightly due to these high transpiration rates and it works well. They definitely use a LOT of water.

A swamp cooler would add humidity and cool.

 

[Crooked8]

these dudes know things

 

[Ca++]

It's hard to get real figures to work with. The DOE (government body) say 5-15 degree drops are possible with a little portable. While 15-40 is possible. Other papers suggest a degree drop is accompanied by a 2-3% RH increase. These are favourable numbers for a desert property.

Evaporative Coolers

In warm climates with low humidity, evaporative coolers can be a cost-effective cooling strategy.

www.energy.gov

I had one of the spinning ones. Something like a cage fan, with capillary matting around it. Dipped into the water. That thing fogged, and you could feel the cooling effect a lot. Even a desk top ultrasonic has a cooling effect.

 

[Douglas.Curtis]

Swamp coolers are nasty. Like I said, I live in the desert and I've been around them for decades.

What do you want? Do you want to pack bowls all day, or would you rather pack a couple bat-loads you take tokes off of occasionally? Yeah the yield is lower when you don't veg to size. I personally don't give a crap, because my grown lasts significantly longer than hot/wet grown.

The down side of cool/dry grown is I have to constantly clean out my bats (edit: Bats, as in one-hitter style smoking bat) on the daily. (Gosh I miss my cannabis. *sigh*)

 

[Ca++]

Bats.

Hmm.

What does that mean over there?

 

[goingrey]

Bats.

Hmm.

What does that mean over there?

Same as everywhere: one hitter pipe.

 

[Crooked8]

Bats.

Hmm.

What does that mean over there?

A chillum, straight pipe, a pipe shaped like a baseball bat.

 

[goingrey]

A chillum, straight pipe, a pipe shaped like a baseball bat.

You don't play tennis with a baseball bat. Hit once and you're off.

 

[Ca++]

The notion of the growing something 5 times stronger, is bats.

 

[farmerlion]

My VPD is too humid by about 10 points, it's 60% and should be 50% humidity. I am wondering if this affects the quality of the flowers by allowing moisture to enter through the leaves instead of being sucked up by the roots, along with the nutes.

Is that why a lower RH is suggested for flower?

Ventilation, Ventilation, Ventilation
Get the air moving so it can transpire.
Peace farmerlion