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How are people running such intense ppfd?!!

Loopusmagpie2u 73 Replies 15,708 Views
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Page 2 of 4 · Replies 21–40 of 74
#21
Watering is another hugely impactful variable as is media.

Read here.

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Marijuana Watering, how media, pot size/shape and environment affect it

Discuss different watering methods for growing your own weed from seeds. Our community members give helpful tips on how pot size and material, as well as environmental factors affect growing cannabis.
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Going through all environmental parameters will allow you to what we call dial in your grow. This changes with genetics and stage of growth. All the info you read is a general guide and should get you in the ballpark if you understand and use it properly….

Key point VPD is only beneficial if you apply it properly and soooo many do not. You must take leaf temp into the equation. These grow equipment reading of VPD leave a lot of room for error. By as much as 15% or more humidity and thats a massive difference in the uptake and transportation if nutrients.

For the record 75-77f LEAF temps is your goal not an arbitrary room temp. Again it gets you close but some must run room temps of 75F to reach those leaf temps and some can run 90F and reach those leafs temps. Using an IR temp gun that costs $20 takes the guess work out
 
#23
Every vpd chart I see says for veg
Aqua Man said:
Under LED when in doubt run 50-55% RH and 75-80F air temps.

What media are you in?
Click to expand...
that low rh? Every vpd chart i see says .8-1 for vpd and my leaf temps are 78* that puts me between 70-75% humidity for late veg growth on the chart I have. Im in nectar for the gods #4 soil. Thanks for the replys
 
#24
I have never purposefully run 75% RH on anything other than seedlings.

If you lower RH, respiration will go up. If the problem is a lack of nutrients, you will get more to the places that need them. If your problem is an over-abundance or a lock out, lowering RH can actually make it worse when you turn the water flow up thru the plant.

I'm not sure what you have there, too much or too little - I'll step aside and let the soil growers help you on that 😉
 
#26
Loopusmagpie2u said:
My rooms conditions are spot on with vpd, co2 and feeding regimen. Any time i try to get lights in the optimal ppfd range all my leaf tips turn over and turn yellow on all my new growth. My room is 82* 72%rh 1200 co2. Im growing in soil with nectar for the gods. My soil slurries are 6.5ph and 400ppm. Im in late veg and I cant get lights over 250ppfd. I turned them up to 300ppfd and this is what happensView attachment 1263036View attachment 1263037View attachment 1263038
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I dont know what calculations you are using but it most certainly does NOT put you at 0.8-1…. It puts you at 0.48 and thats NOT ok
 
#27
Moe.Red said:
As you increase light, plant processes increase.

Photosynthesis (assuming you have CO2 and H2O present in sufficient qty 6CO2 + 6H2O → C6H12O6 + 6O2) CO2 yes, H2O good?
Respiration
Other stuff

I think you might be looking at an issue in the root zone that is exacerbated and only shows up with higher respiration.

Also your RH is a bit high making VPD a bit low, meaning the stomata are open but there is so much water in the air that there is not good gas exchange. If you increase the lights, temp goes up meaning RH goes down, VPD goes up, so respiration is restored. In that scenario, if your nutes were out of balance or not enough O2 in root zone, it could look like this and it is not really PPFD doing it, but rather the higher leaf temps and lower RH.

I'm thinking that if your VPD was on point and your watering / nutes / root zone oxygenation was all perfect you could bring that light way up.

It's a friggin balancing act man.

TLDR - I think the problem is actually in the root zone.
Click to expand...
Nice
 
#31
Aqua Man said:
I dont know what calculations you are using but it most certainly does NOT put you at 0.8-1…. It puts you at 0.48 and thats NOT ok
Click to expand...
What chart are you using apprently the one im using is way off? It says if room temps 82 stay between 65% and 75% for late veg early flower. Do you have a better chart I can snag from ya? thanks.
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#32
Loopusmagpie2u said:
What chart are you using apprently the one im using is way off? It says if room temps 82 stay between 65% and 75% for late veg early flower. Do you have a better chart I can snag from ya? thanks.View attachment 1263542
Click to expand...
82 air under LED give a leaf temp of maybe -4 air temp - really need leaf temp for this equation. But assuming 82-4 = 78 leaf temp and 72 RH = leaf VPD of .59 kPa At this stage you should be hovering around 1.
 
#33
Loopusmagpie2u said:
What chart are you using apprently the one im using is way off? It says if room temps 82 stay between 65% and 75% for late veg early flower. Do you have a better chart I can snag from ya? thanks.View attachment 1263542
Click to expand...
In this thread there is a calculator app link, or follow the directions i posted to make one, Or use this one.

www.dimluxlighting.com

Vapor Pressure Deficit VPD Calculator - Dimlux Lighting - The Best Grow Lights

Vapor Pressure DeficitCalculator Calculate both Room VPD and Leaf VPD automatically Just enter the value below to generate the VPD values for your room and your plants. You’ll need to know the room’s temperature, relative humidity, and the plant’s temperature. We recommend calibrating your...
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VPD (vapor pressure deficit)

Ok i was gonna sit down and write out a whole article but i have been lazy so instead instead I'm going to copy paste because im lazy. This is not my work so let start. You may find this very long but its worth the read. Some may want to skip ahead. I have added here and there to what i feel is...
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#34
Loopusmagpie2u said:
What chart are you using apprently the one im using is way off? It says if room temps 82 stay between 65% and 75% for late veg early flower. Do you have a better chart I can snag from ya? thanks.View attachment 1263542
Click to expand...
Ok see this chart on the top left it says leaf cooler than air temp by 1f. Well you leaf temps are likely about 77-78f which would be a difference of about 4-5f cooler as is typical under LED. I cannot stress how much difference leaf temps make in this equation.
 
#35
Aqua Man said:
Ok see this chart on the top left it says leaf cooler than air temp by 1f. Well you leaf temps are likely about 77-78f which would be a difference of about 4-5f cooler as is typical under LED. I cannot stress how much difference leaf temps make in this equation.
Click to expand...
And as respiration goes up, leaf temps drop as the water acts as a cooler. Its not a set it and forget it thing. If you drop RH and respiration increases, the delta between air temp and leaf temp also goes up.
 
#37
Madmax said:
U mean leaf temp will b closer to air temp moe?actually im confused 😆
Click to expand...
No. leaf temps drop.

Water acts as a coolant. If proper VPD is maintained and respiration is high, it's like sweat evaporating from your skin.

Bear with me...

Lets say you measure your leaf temp at 75* and ambient at 78*. But RH is too high to allow for proper respiration.

Adjust RH down.

Respiration goes up

Leafs get cooled by water

Now you are at 73* leaf temps but ambient has not changed. You now have to recalculate VPD.

Its the leaf temp that matters, not the ambient. And LED is way different than HPS, most LED have no iR to heat things up radiantly which HPS has lots of.
 
#38
I'll add it is actually the bottom of the leaf where the stomata are most numerous, so this assumes you have circulation fans that prevent a micro climate of wet air around the leaves. If you have zero air movement, the water from respiration sits right there under the leaf creating a spot of high RH - which again blows up your VPD calcs. So it is a balancing act and once you internalize how this all works together, your grows will improve.
 
#39
Im going to get an ir gun today so i know whats going on.ive been winging it for 2 yrs lol.ive finally got rh down between 44%-50% .air temps set at 26.4 extraction fan comes on at 26.7..im bit past mid flower at 5 weeks since bud onset .lights at 21" to canopy
 
#40
Madmax said:
Im going to get an ir gun today so i know whats going on.ive been winging it for 2 yrs lol.ive finally got rh down between 44%-50% .air temps set at 26.4 extraction fan comes on at 26.7..im bit past mid flower at 5 weeks since bud onset .lights at 21" to canopy
Click to expand...
Most underrated tool for growing and its cheap.

Evaporative cooling is huge
 
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