Thoughts on VPD? I'm not sold on it.

[Delps8]

I'm keeping all variables identical to my previous grow where I was locked on to 1.0 during veg. My EC/nutrients are the exact same down to the ml. I kept paper notes so I'd be able to do a 1:1 comparison. The only thing that changed is the RH, which in turn results in the higher 1.4 VPD value.

I guess one other change is the feeding frequency, but that's out of necessity since they drink more at 1.4 and need to be watered more often as the coco dries out faster. So even though they're getting the same nutrient ratios to the ml, the 1.4 veg is technically getting more accumulated nutrients since the feedings are more frequent. I water on an as needed basis, judging by the weight of the pots. Before each new feeding, I always let the coco get fairly dry, but not bone dry to the point where there's any wilting.

The veg solution they get is Canna Coco A + B, Rhizotonic, Roots Excelurator, CalMag, ProTekt silica, Cannazym, Thrive Alive B-1 Red (nutrient and foliar), and Great White. The Great White isn't as effective in coco as it would be in a soil blend, but it still helps the root zone to a degree. I've noticed I get finer root hairs with Rhizotonic and more hearty roots with Roots Excelurator, so I rotate between the two every other feeding. I don't combine them in the same solution.

The previous 1.0 and current 1.4 both receive the exact same foliar feeding, which is a daily foliar feeding of Thrive Alive B-1 Red. They get a foliar feed each day, right when the lights come on. The light is dimmed to 25% for the first hour to avoid burning the leaves. After an hour, there are no more droplets on the leaves acting as magnifying glasses, so it's safe to bump up the light intensity, which I dial to 50% for the first week of veg and then bump to 75% for the remainder of veg.

Which reduces their ability to grow because they're not getting light for that time period but that's a separate issue.

I'm not measuring height with a ruler, but I'm able to tell that the growth is faster because the plants reached my trellis grid sooner, which remains at the same height as last round. In other words, I know the growth is faster because with VPD at 1.0, the plants reached the trellis on day 16, whereas the current plants at 1.4 reached the trellis in 13 days. It's not a huge difference, but mildly substantial with the plants at 1.4 reaching the same size around 19% faster.

Interesting that they're growing taller sooner but what about yield?

Another upside is that at 55% RH, it's not too far off from my air conditioned lung room, so my humidifier only kicks on sparingly to counter the incoming dry AC air which floats between 45-50% RH. With 1.0 VPD, my humidifier was almost always running to maintain 67% RH, so I was having to buy a lot more distilled water.

Understood but those are components of VPD.

Question I should have asked from the start - seeds or clones? If it's seeds then all bets are off but if it's clones, the next step would be to compare harvest weight and then dried weight for above ground mass and then flower only.

Interesting situation but, when all it said and done, if it works for you, take the win.

 

[Delps8]

Agreed. It's not like people didn't grow good bud before vpd was a thing.

And whether or not VPD had been formulated (I think it was in th 1930's), growers were still keeping their temps and RH within certain ranges and, therefore, they were keeping their VPD in range.

VPD is just one number that covers a range of temperature and RH combinations. So if you're keeping your temp "in check" and keeping RH in "about the mid-50's" that's exactly the same as keeping VPD at around 1.0 (veg).

It's not magic, it's just one number instead of two.

 

[SBNDB]

Usually for me i just shoot for 80f/60rh and thats usually good enough to get nice results, with airflow and just a little cleanliness theres never any mold problems. Knock on wood.

 

[tstick]

VPD works great for new growers and growers who see things mathematically. It gives them something to shoot for in terms of trying to get to the "ideal" number. Other growers who are older and learned before the concept of VPD existed, might use more of an intuition to "feel" what the plants are asking for or what to check if something is going wrong -just from years of trial and error. After awhile, you get a sense of what''s going on....the light is too intense....it's too warm....not enough humidity....and so on. My guess is that an experienced, intuitive grower and an experienced, mathematically-minded grower will ultimately get to the same result within a few grams.

 

[Delps8]

VPD works great for new growers and growers who see things mathematically. It gives them something to shoot for in terms of trying to get to the "ideal" number. Other growers who are older and learned before the concept of VPD existed, might use more of an intuition to "feel" what the plants are asking for or what to check if something is going wrong -just from years of trial and error. After awhile, you just get a sense of what''s going on....the light is too intense....it's too warm....not enough humidity....and so on. My guess is that an experienced, intuitive grower and an experienced, mathematically-minded grower will ultimately get to the same result within a few grams.

"My guess is that an experienced, intuitive grower and an experienced, mathematically-minded grower will ultimately get to the same result within a few grams."

No doubt, for the simple reason that they're just different labels for the exact same thing. A VPD of 1.0 is one number to describe combinations of temperature and humidity that range from 95° and 76% humidity to 61° and 36% humidity.

If one person is driving at 62 MPH and someone else is driving 100 KPH, who's driving faster?

 

[Kushash]

"My guess is that an experienced, intuitive grower and an experienced, mathematically-minded grower will ultimately get to the same result within a few grams."

No doubt, for the simple reason that they're just different labels for the exact same thing. A VPD of 1.0 is one number to describe combinations of temperature and humidity that range from 95° and 76% humidity to 61° and 36% humidity.

If one person is driving at 62 MPH and someone else is driving 100 KPH, who's driving faster?

The one who is going 100 KPH.

 

[Delps8]

The one who is going 100 KPH.

You cheated. You saw that he was driving a red car.

 

[Mumbeltypeg]

No one said vpd could be why my colas are dying and drying out but no mold whatsoever even used a magnifying glass.

My vpd is in the red. I guess this is my first summer grow of this magnitude. I may of only one other time on a hobby one plant scale but didnt have heat issues or I simply never grew during summer.

too dry, too hot.. drop temps, bump humidity, halve nutes till you get it right.

 

[medidedicated]

I would but perpetual flower room 3 diff tents not always in line. It would be a relief IMO to write it off as a vpd problem its what I hoped to hear coming here not to hijack. Its on topic though.

My rh drops few weeks from chop or at least the last few strains Ive run. edt only thing I just thought of is effected colas are closer to light than usual but idk. So were sites further away.

 

[GenericEnigma]

VPD is real, but not as important as the balance between light, temp, humidity, and ppm.

For example, if you are getting nute burn at 80dF and 40%RH with a 600W LED, you could lower the ppm, raise the RH, lower the temp, or turn down the light. Same result, more or less.

If you want to talk yield, that's a different story.

 

[raggyb]

I'm back into growing after a 10 year hiatus and have been researching new industry techniques and all anybody talks about now is VPD, but I'm not sold on it.

Anybody else having better results by ignoring VPD altogether and going with temps and humidity levels that are off the recommended "VPD Chart" spectrum?

I tried to chase VPD but found it to be counterproductive and was getting slow growth rates. As soon as I went back to my tried and true methods, and started ignoring VPD, my growth rates and overall plant health improved. I was going off the "Pulse" chart, which had veg pegged at a 0.9 to 1.1 VPD, but that was resulting in underwhelming growth rates and overall plant health for me. I switched to my preferred temps and humidity as a starting point, which hovers around 1.4 VPD on the chart, and all of a sudden my plants are thriving like I'm used to.

I'm interested to hear what other people think about VPD. VPD in my mind seems like marketing since every strain I've ever grown has different needs and can't be confined to a one-size-fits-all chart. I know there's science behind it, but I have a fully controlled environment and had my VPD on point (according to the Pulse chart) and the plants were not loving it. My current veg VPD is more aligned with the recommended flowering VPD numbers and is doing much better than the recommended veg VPD.

Shouldn't you increase the nutes when you lower the vpd to 0.9, so that nutrient uptake is the same as what works well for you at 1.4 vpd? Hard to control that unless hydroponic. Or alternatively, if someone is in soil and always getting lockout, then perhaps keep the soil mix as is and lower the vpd would slow nutrient uptake. Saying probably because it's not necessarily 1 to 1 how quantity of nutrients in the soil relates to quantity of nutrient uptake. Perhaps vpd and temps effect the balance of mychos, bacteria, fungi etc...

On flowering, I've never seen comments on is what vpd changes do to effect mold growth. Like the basic rH only advice is to flower at 45%. But can you raise rH higher than that if your temps are higher to get back to whatever constant vpd would be equal to the 45% rH at 76F and still avoid mold? The basic statement is mold thrives in humidity, but that does not seem to be addressing factors like the rate of evaporaton on the leaf it grows on, state of stomata,...etc., which might also effect mold growth. Seen any studies on that?

 

[Rocket Soul]

I'm back into growing after a 10 year hiatus and have been researching new industry techniques and all anybody talks about now is VPD, but I'm not sold on it.

Anybody else having better results by ignoring VPD altogether and going with temps and humidity levels that are off the recommended "VPD Chart" spectrum?

I tried to chase VPD but found it to be counterproductive and was getting slow growth rates. As soon as I went back to my tried and true methods, and started ignoring VPD, my growth rates and overall plant health improved. I was going off the "Pulse" chart, which had veg pegged at a 0.9 to 1.1 VPD, but that was resulting in underwhelming growth rates and overall plant health for me. I switched to my preferred temps and humidity as a starting point, which hovers around 1.4 VPD on the chart, and all of a sudden my plants are thriving like I'm used to.

I'm interested to hear what other people think about VPD. VPD in my mind seems like marketing since every strain I've ever grown has different needs and can't be confined to a one-size-fits-all chart. I know there's science behind it, but I have a fully controlled environment and had my VPD on point (according to the Pulse chart) and the plants were not loving it. My current veg VPD is more aligned with the recommended flowering VPD numbers and is doing much better than the recommended veg VPD.

Whats your lighting? Cause vpd works differently with HID and and led and depending on light intensity. Not sure what chart you use for reference. Vpdchart.com allows you to adjust leaf temperature; this throws the numbers off by quite a bit. If HID you have a fair bit hotter leaves while led veg is usually colder than ambient. And

Also remember: vpd controls transpiration but is not the only factor. High co2 inhibits stomata aperture, higher blue content and higher light levels will cause it to open more.

Then it also depends a bit on grow philosophy: what do you look at first; plant behaviour or sensors?
You can try to keep an exact temp/rh for what you find is your ideal state. And let the plants grow. Or you can just look at the plants as they grow and ask: am i happy with how they grow and how they look? Are these well transpiring plants? Hows the leaf boner looking to me?
And if not looking good, check vpd for which direction to take your environment to get better growth behaviour. That vpd isnt a goal in itself only the direction to move in when you see plant unhappiness. And when you see happy plants you can just not care about vpd, only care about it when youre not happy with look and progress.

For us who dont have absolute controls over environment in veg and many times use quite low light intensity: there is a point when its cold that some low light trays just wont behave. And pur lights wont warm the environment due to low watts. We throw in a gas heater that usually solves this but check, after the heater goes in our vpd still aligns itself better to the vpd charts.
Try around and see for your self. Old temp / rh advice were very relative to a "total environment" not too humid in flower as to not cause rott and mold and they were based on hid lights. If you push in numbers in vpdchart leaftemps +2-3C degrees youre actually really close to the old timer temp/rh advice.

 

[Rocket Soul]

I'm keeping all variables identical to my previous grow where I was locked on to 1.0 during veg. My EC/nutrients are the exact same down to the ml. I kept paper notes so I'd be able to do a 1:1 comparison. The only thing that changed is the RH, which in turn results in the higher 1.4 VPD value.

I guess one other change is the feeding frequency, but that's out of necessity since they drink more at 1.4 and need to be watered more often as the coco dries out faster. So even though they're getting the same nutrient ratios to the ml, the 1.4 veg is technically getting more accumulated nutrients since the feedings are more frequent. I water on an as needed basis, judging by the weight of the pots. Before each new feeding, I always let the coco get fairly dry, but not bone dry to the point where there's any wilting.

The veg solution they get is Canna Coco A + B, Rhizotonic, Roots Excelurator, CalMag, ProTekt silica, Cannazym, Thrive Alive B-1 Red (nutrient and foliar), and Great White. The Great White isn't as effective in coco as it would be in a soil blend, but it still helps the root zone to a degree. I've noticed I get finer root hairs with Rhizotonic and more hearty roots with Roots Excelurator, so I rotate between the two every other feeding. I don't combine them in the same solution.

The previous 1.0 and current 1.4 both receive the exact same foliar feeding, which is a daily foliar feeding of Thrive Alive B-1 Red. They get a foliar feed each day, right when the lights come on. The light is dimmed to 25% for the first hour to avoid burning the leaves. After an hour, there are no more droplets on the leaves acting as magnifying glasses, so it's safe to bump up the light intensity, which I dial to 50% for the first week of veg and then bump to 75% for the remainder of veg.

I'm not measuring height with a ruler, but I'm able to tell that the growth is faster because the plants reached my trellis grid sooner, which remains at the same height as last round. In other words, I know the growth is faster because with VPD at 1.0, the plants reached the trellis on day 16, whereas the current plants at 1.4 reached the trellis in 13 days. It's not a huge difference, but mildly substantial with the plants at 1.4 reaching the same size around 19% faster.

Another upside is that at 55% RH, it's not too far off from my air conditioned lung room, so my humidifier only kicks on sparingly to counter the incoming dry AC air which floats between 45-50% RH. With 1.0 VPD, my humidifier was almost always running to maintain 67% RH, so I was having to buy a lot more distilled water.

Keeping the nutes same: does that mean that your using the same EC in and getting the same EC out?
Coco: what does your up potting game look like? We always use a fairly high EC in for the first watering of coco to avoid fresh coco hogging the nutes; this is how we got rid of a lot of deficiencies. You need to focus at least as much on your ec out/runoff as your ec in.