Is RH Really Such a Big Deal?

[jumpincactus]

Recently I have seen a lot of posts about relative humidity and the importance of it being in the proper Zone. I have grown in relative humidity levels from as low as 10 or 15% in the winter, to as much as 80% in the summer, and I find that I see very little difference at all in yield or potency of the plants. They seem to react the same regardless, with the possible exception of when they first start I might see a little bit of tip Browning which quickly dissipates as the leaves fill in more. I grow mostly Sativa strains, so perhaps that has something to do with the lack of problems. In truth, my rh rarely goes above 30% and no issues seem present. Why do some seem to have problems... it seems higher Rh causes more problems, like PM and similar maladys.
What is your experience?

look at my avatar it was grown in an avg 6% Rh

 

[Dirtbag]

The bests explanation on the effect of rh on plants I could find was plants work on hydraulics. With a high rh the plants needed water is absorbed through the leaves slowing down its need to draw water and nutrients from the roots leaving a build up of nutrients behind in the soil that then can lead to nutrient lockout.

Yeah not quite, but close.

I think Everest does a good job explaining this subject.

 

[jumpincactus]

VPD is valid science. At the end of the day many grow great erb and are no where near the ideal vpds some would have us believe we need to grow good erb. I live in a very arid enviro and I am never anywhere near ideal vpd levels but that doesnt stop the fire from ragin!!! I would have to drop thousands to achieve any where near perfect conditions. Wonder how the afghanis hit ther vpds over there and still threw down some killer smoke.

 

[xPeacePipex]

VPD seems to be tossed around a lot with few following the actual protocol. I don't think it should be applied with a small grow and the inexperienced in general as it can be counterproductive then. Most that adhere to this have proven cuts that have extreme mold resistance and a lot more experience with this all then say the typical home growers just looking to produce enough for personal use.

Back when I had nothing but a closest to grow in during my youth I didn't have the advantages of ventilation, let alone room for oscillating fans. After moving forward in life and building larger setups I began to note that some things did really grow better in that old humid closet and it was VPD always at the constant perfect value even though I lived in what seemed like a jungle. Same thing was observed with the specimens that I took home from the greenhouse I worked in back then regardless of how much light and feed I supplied.

Ironically, the only time I have ever had issues with high humidity and mold was with the modern mixes and towards the later of my years growing inside and out. Never had issues with the old land races, cultivars as well as even the earliest of commercialized stock obtained in the early 90's. With today's poly x poly and the incestuous trends I find that running with the VPD dialed in can be a hit and miss due to lack of resistance that isn't always "strain dependent" as it is then Pheno dependent. Even the Mexican hybrids of the 90's were very resistant and strong in comparison with the mutts called hybrids today.

Perhaps the axiom of bigger is better is the problem, it's an American thing for sure. Bigger buds equals bigger risks on an average indoor and outdoor. This is another thing I believe is a factor in this all. Big Bud, it was a very popular type for a reason and the trend never died, even if the big bud hype died quickly. Everyone seems to want the biggest dense of flowers, even though on average high quality cannabis is moderate yielding at best. I have seen plenty of the modern types mold in 50% RH due to density and trapped moisture in the flowers regardless of air activity, yet again I have never seen it with the older stock.

So much of the paradigm surrounding growing cannabis can't always be taken for face value, subjectively each grower should be doing what works for them, their plants and the goals sought without adherence to the mainstream..

 

[AlexGrowns]

Recently I have seen a lot of posts about relative humidity and the importance of it being in the proper Zone. I have grown in relative humidity levels from as low as 10 or 15% in the winter, to as much as 80% in the summer, and I find that I see very little difference at all in yield or potency of the plants. They seem to react the same regardless, with the possible exception of when they first start I might see a little bit of tip Browning which quickly dissipates as the leaves fill in more. I grow mostly Sativa strains, so perhaps that has something to do with the lack of problems. In truth, my rh rarely goes above 30% and no issues seem present. Why do some seem to have problems... it seems higher Rh causes more problems, like PM and similar maladys.
What is your experience?

Honestly I think as long as it's not humid enough to form water droplets it's not gonna mold, outdoors the dew/rain ect I suspect are killers, I've vegged in 19% and it only seemed slightly stressed compared to when I dialed it in to 50-60%, I'm a noob but I was wondering if it's something that matters but isn't very important. The first time my tent went up to 75% at night I freaked and almost thought I would open up a tent full of white and brown fluff haha man I was an idiot a few months ago lol

 

[Aqua Man]

VPD seems to be tossed around a lot with few following the actual protocol. I don't think it should be applied with a small grow and the inexperienced in general as it can be counterproductive then. Most that adhere to this have proven cuts that have extreme mold resistance and a lot more experience with this all then say the typical home growers just looking to produce enough for personal use.

Back when I had nothing but a closest to grow in during my youth I didn't have the advantages of ventilation, let alone room for oscillating fans. After moving forward in life and building larger setups I began to note that some things did really grow better in that old humid closet and it was VPD always at the constant perfect value even though I lived in what seemed like a jungle. Same thing was observed with the specimens that I took home from the greenhouse I worked in back then regardless of how much light and feed I supplied.

Ironically, the only time I have ever had issues with high humidity and mold was with the modern mixes and towards the later of my years growing inside and out. Never had issues with the old land races, cultivars as well as even the earliest of commercialized stock obtained in the early 90's. With today's poly x poly and the incestuous trends I find that running with the VPD dialed in can be a hit and miss due to lack of resistance that isn't always "strain dependent" as it is then Pheno dependent. Even the Mexican hybrids of the 90's were very resistant and strong in comparison with the mutts called hybrids today.

Perhaps the axiom of bigger is better is the problem, it's an American thing for sure. Bigger buds equals bigger risks on an average indoor and outdoor. This is another thing I believe is a factor in this all. Big Bud, it was a very popular type for a reason and the trend never died, even if the big bud hype died quickly. Everyone seems to want the biggest dense of flowers, even though on average high quality cannabis is moderate yielding at best. I have seen plenty of the modern types mold in 50% RH due to density and trapped moisture in the flowers regardless of air activity, yet again I have never seen it with the older stock.

So much of the paradigm surrounding growing cannabis can't always be taken for face value, subjectively each grower should be doing what works for them, their plants and the goals sought without adherence to the mainstream..

I absolutely agree that VPD has some increased risks and genetics play a huge role.

This is part of what I was saying soo many people do it wrong. Some more resistant strains have no problem sitting at the higher end of RH of VPD while others should be near the lower RH of VPD. VPD is a guideline in my eyes and yes I would say its better to suited to an experienced grower.

However like I said previously the more dialed in the setup the more benefit you can see from it. The faster your growth the more beneficial this becomes.

Probably the biggest most common mistake is not taking leaf temps into account. The charts floating around have the RH way to high and you would be surprised at the actual RH needed being much lower than those charts when using it properly. It's really not as high as people think and the reason people think it's that high is the charts floating around.

 

[Aqua Man]

Here is an example. Veg kpa of .8 to 1.1 is recommended. .8 would be the higher RH and 1.1 would be the lower RH for the range.

I keep my temps at about 80f to achieve 75f leaf temps (ideal leaf temp for cannabis) to achieve 0.875 which is the higher end of RH of the suggested .8-1.1 for veg I need an RH of 60%

air temp 80F
Leaf temp 75
RH 60%

Provides a proper kpa on the high side of the RH recommendations.

Does this sound like moldy conditions? Nope people use it wrong that is all.

 

[Dirtbag]

I find it wild that my experience is so different. I've had the same selections of strains for almost a decade and have grown them every which way and they always grow faster with bigger leaves and stems with higher humidity in veg.
My friend that turned me onto it has been growing indoors with a VERY large operation for decades and no shit he runs his veg rooms close to 80%, mind you he does puff sulphur in veg to prevent mildew, as do I. But having grown in low humidity and high, there is no question in my mind, the strains I've grown at least grow way better in veg with humidity 60-70%.

I'm not saying lower humidity will be bad and cause a lot of issues unless you're overfeeding, just that higher humidity IME, the plants grow faster and look happier. In flower, I keep it 40-50%

 

[Aqua Man]

I find it wild that my experience is so different. I've had the same selections of strains for almost a decade and have grown them every which way and they always grow faster with bigger leaves and stems with higher humidity in veg.
My friend that turned me onto it has been growing indoors with a VERY large operation for decades and no shit he runs his veg rooms close to 80%, mind you he does puff sulphur in veg to prevent mildew, as do I. But having grown in low humidity and high, there is no question in my mind, the strains I've grown at least grow way better in veg with humidity 60-70%.

I'm not saying lower humidity will be bad and cause a lot of issues unless you're overfeeding, just that higher humidity IME, the plants grow faster and look happier. In flower, I keep it 40-50%

I agree. The type of lighting plays a big role in this also. The more IR the higher your RH. I run led and see about 5-8f difference in leaf temp from air temp. Same setup you change to HPS, MH or CMH will all change the leaf temps differently. So you will need a higher RH with all 3 of those but all 3 will be different.

Again you can't go by those charts floating around. You must calculate based on your setup.

 

[Aqua Man]

Just to add here because time expired to edit.

My air temp at 80f taking leaf temps into account calls for 60% RH.

My air temp at 80f NOT taking leaf temps into account calls for 75%.

Big difference and this is why people have issues with VPD.

 

[Terpeneluv]

Great thread.

I find this article helpful, especially if you're new like myself. (His videos are great too)

 

[Dirtbag]

I'd have to agree those charts arent really trustworthy, you should really do the math with all 3 variables if you're going to play the game.

I'll also add, my buddy runs his rooms a bit warm with 1500ppm Co2 also, which also makes a difference. I wouldnt recommend anyone running almost 80%RH without warm temps, co2 and sulphur.

 

[jumpincactus]

VPD seems to be tossed around a lot with few following the actual protocol. I don't think it should be applied with a small grow and the inexperienced in general as it can be counterproductive then. Most that adhere to this have proven cuts that have extreme mold resistance and a lot more experience with this all then say the typical home growers just looking to produce enough for personal use.

Back when I had nothing but a closest to grow in during my youth I didn't have the advantages of ventilation, let alone room for oscillating fans. After moving forward in life and building larger setups I began to note that some things did really grow better in that old humid closet and it was VPD always at the constant perfect value even though I lived in what seemed like a jungle. Same thing was observed with the specimens that I took home from the greenhouse I worked in back then regardless of how much light and feed I supplied.

Ironically, the only time I have ever had issues with high humidity and mold was with the modern mixes and towards the later of my years growing inside and out. Never had issues with the old land races, cultivars as well as even the earliest of commercialized stock obtained in the early 90's. With today's poly x poly and the incestuous trends I find that running with the VPD dialed in can be a hit and miss due to lack of resistance that isn't always "strain dependent" as it is then Pheno dependent. Even the Mexican hybrids of the 90's were very resistant and strong in comparison with the mutts called hybrids today.

Perhaps the axiom of bigger is better is the problem, it's an American thing for sure. Bigger buds equals bigger risks on an average indoor and outdoor. This is another thing I believe is a factor in this all. Big Bud, it was a very popular type for a reason and the trend never died, even if the big bud hype died quickly. Everyone seems to want the biggest dense of flowers, even though on average high quality cannabis is moderate yielding at best. I have seen plenty of the modern types mold in 50% RH due to density and trapped moisture in the flowers regardless of air activity, yet again I have never seen it with the older stock.

So much of the paradigm surrounding growing cannabis can't always be taken for face value, subjectively each grower should be doing what works for them, their plants and the goals sought without adherence to the mainstream..

Well said man.

 

[oldskol4evr]

VPD is valid science. At the end of the day many grow great erb and are no where near the ideal vpds some would have us believe we need to grow good erb. I live in a very arid enviro and I am never anywhere near ideal vpd levels but that doesnt stop the fire from ragin!!! I would have to drop thousands to achieve any where near perfect conditions. Wonder how the afghanis hit ther vpds over there and still threw down some killer smoke.

bingo you called it bro,i been to both places at least in afganistan that have mountians area but still very very freaking hot,temps sore to 150 during day same as iraq,thing is there is no humidity none,wind blows the sand storms appear along with the little folk that dont wont us there right behind it,first they come in with mortars then leg it in there,so no wind is best,cold as hell and it does snow in the desert and you think it shut down most towns here ha you can even get the hyienas to move ,no movement at all,but yet someof the best herb in the world comes from there,most is down in the mountains but it still hot as crap,surprisinly the sudden drop from 150 to 100 at night doesnt effect them much,all the time i was there it never got dark,no shit darkness is like a complete full moon here,150 day 100 at night the plants do amazing work if you can find any plant life at all,i had a favorite tree in iraq,gunny said boy that a damn bush it was but my make believe oak tree hahaah just sitting in the middle of the desert nothing but sand for as far as you could see ,the one tree hahahh,knowing this is why i was convinced by gt21 with growing in forced wind,none of the bells or whistles,only heat in winter is the light only ac is the shade from the utility room they grow in ,that it,since then throw a seed in soil and roll it dont make ,it done plant another,my mind says best breeding stock is the one that survies the heat,your a desert rat you feel what im saying,lmao

 

[jumpincactus]

indeed i do. Desert dawg/ desert rat thru and thru. :):fire: