Old Strains - New LED Light!

[Gee64]

@Gee64 So you are saying that the puls chart is using room RH and leaf temp where the chart I pulled up is using room RH and room temp? Didn't catch the room VPD because it was just the first result on a google search. That would explain why the calculators that use 3 variables never quite match the charts that only use 2 variables. Two charts using a different temp variable wouldn't match each other.

Never actually checked, but I just assumed, leaf temp would be near ambient under LED. I just put that into the HID and greenhouse variable. You are right. Even the subtle difference of LED light would skew the chart. Happened to set a meter at canopy height yesterday for a different test and it is currently 3 deg hotter than the room.

@Sativa1970 's question is very valid and very common so I will answer it, but my intention isn't to bog your journal down, so here goes, and I will gladly discuss this in private or over at GeeSpot if anyone needs help with it.

So Sativa, to answer your question,Yeah exactly. Reread the pulse manual just above the chart, it states that the chart is based on a zero degree offset, that's room VPD. It's how they predict weather.

You want plant VPD. It's a different formula with different outcomes. The meter uses both formulas and flips between the 2 without you knowing when you use or don't use an offset, so you can use the one meter for 2 very different purposes. Thats how the meters get growers in trouble. It's not the meters fault, it's operating perfectly.

If you are using an app calculator you want the one with 3 data points. Air temp, leaf temp, and RH.

If you dial in your plants VPD you automatically get an optimal room VPD but if you dial in room VPD you never get optimal plant VPD.

So the charts and meters mislead you and you do everything right but your grow still sucks, and you just can't figure it out.

It's because you didn't use the right formula, or if you did you didn't realize that plants change their leaf temps all day long, and you set your VPD too early in the day. 10 hours after lights on is where you want to see optimal plant VPD as compared to the right chart. Thats when they adjust their stomata to run at their highest VPD of the day.

1st thing in the day the leaf temps will be equal to or higher than air temp. Plants do this to flip between transpiration and respiration. They reverse themselves. As the day progresses this changes.

So late in the day the plant is working hard. If you mistakenly got the formula wrong it will be working far harder than you think. Too hard.

By mid flower your grow will suck and you will be chasing your tail trying to figure it out but you won't be able to.

It's because Plant VPD is the throttle to the plant and if you over accelerate it the weakest link pops up quickly.
Usually it's a deficiency that you can't correct no matter how hard you try.

It's because you are running the plant faster than the roots can keep up so it's not really a deficiency, it's an uptake restriction that shows as a deficiency.

You are forcing the plant to grow faster than the roots can keep up too.

More nutes won't fix it, only throttling the plant down will.

If you use an IR gun on your leaves all day long every day you will be amazed at whats are going on. If you change nothing and leaf temp differential goes from 2 degrees to 1 or zero for an unexplained reason, grab your moisture probe, she probably wants a drink. That sorta thing.

If she doesn't need a drink grab your light meter, she likely stretched too close to the light.

If it's neither she's sick and running a fever, you need to figure her out. Probably salt buildup or bugs.

Low calcium will make a plants tolerance for light become less, so grab your refractometer and check calcium.

VPD is incredible, just make sure you are true to plant VPD.

Almost everyone gets this wrong in the beginning and it's because most internet data on VPD and most real world applications of VPD aren't about growing plants, it's about weather, so confusion is rampant. It's no ones fault, it just is what it is.

If you add or subtract light, the actual offset from leaf temp to air temp will become greater or lesser, and that offset is the part of the equation that has the largest multiplier attached to it, so light intensity becomes the most dramatic volatile part, whether it be too much light for what the roots can handle, or not enough light to make the plant grow very well.

A healthy plant will do everything it can to try to maintain a 2 degree offset when it's working hard because physics dictates that plant transpiration works best at a 2 degree offset.

It forces the atmosphere to suck on the stomata in the sweet spot for proper transpiration from cool leaf to warmer air.

So if light is more intense than the roots can keep up to, the light striking the leaf and not being used for photosynthesis causes resistance, and it converts to heat and raises the leaf temp which raises VPD, speeds the plant up, and exagerates the issue.

LED's gave us the ability to suddenly have too much light, combine that with the wrong charts, and here we are.

Once your light is adjusted to solidify a 2 degree offset after 10 hours of lights on, RH is the easiest way to manipulate VPD to dial it in while maintaining your 2 degree offset.

Then she grows like a bandit praying nicely.

If you tried all that and VPD is still wacky or more to the point your leaves are too hot, check calcium again.

 

[Sativa1970]

It was never my intention to send Chuckeyes thread down a rabbit hole. I was just looking for the leading cause of the inconsistency in charts. The inconsistency boils down to how many factors you enter into the equation. Room temp and RH are the fundamental start and leaf temp refines it. Other factors will change your readings or slightly skew the chart. Air flow will lower temp and RH at the leaf surface, not the room. Aired strains have smaller stigmata than tropical strains effecting volume of moisture released at the leaf surface from photo activity. Circulatory health, peak productivity, availability of water and nutrients in the media to replenish the leaves. The list of minor variables goes on and on.

A few major factors fallowed by a death of a thousand cuts. The major ones were what I was trying to define. Thank you all for entertaining my question. I will now return you to the previously scheduled programing.

 

[Sativa1970]

So I kept the goal in mind and once Lambs Bread and I got cutting I had to slow down when I lost count of where I was, he, he...

I missed this post some how. Smoking lambs bread or just keeping a "lambs bread" attitude? Mowi, Lambs Bread, Panama red, Jack Herer, and Thai are my top 5. Always a little jar of each, out on the table.

 

[Chuckeye]

I missed this post some how. Smoking lambs bread or just keeping a "lambs bread" attitude? Mowi, Lambs Bread, Panama red, Jack Herer, and Thai are my top 5. Always a little jar of each, out on the table.

Smoking Lambs Bread to adjust my attitude

I have a wide choice and still keep coming back to Lambs Bread and then Apple Betty and then......

Pretty sure Apple Betty and I are going to start training on two more Girls tonight

Should be interesting, they are only 7" and 8" high but have a healthy sixth node !

Cheers

 

[Delps8]

As for the VPD stuff, it peaks my interest and I enjoy learning new things; but I treat it as one of those things I’ve gotten by without knowing of it for a long time so I’m not going to kill myself learning all I can like a Netflix binge but I’ll definitely gradually take it in and try to leverage any new knowledge just can gain as an opportunity to improve going forward. Pretty much my attitude about anything

VPD, itself, is the tip of the iceberg. Everywhere you see "VPD", you can substitute "temperature and RH" because that's all that it is.

It doesn't take a lot of effort to learn about VPD but, what I have seen for years, is that it takes effort to start to learn about VPD.

VPD isn't the issue, from what I see. Learning about VPD is a fine, though short, academic exercise. The bigger issue is growers who use VPD as a means of controlling or, as in my case, influencing, the grow environment vs growers who don't want to do so because "it's always worked fine in the past".

VPD is useful for keeping a grow environment "optimized" (how much of a benefit is a useful discussion) but it's a way to improve outcomes. A lot of growers do not need to improve their outcomes because they have great temp and RH values. Some growers would benefit from improving their grows but simply refuse to admit it.

A different look at this is bound up in "read the plants". That's a valuable skill but, if that approach is used to control how a grower…conducts his grow, that will lead to issues, over the long haul unless the grower has one of those great, stable environments.

Why's that?

Because "read the plants" is fraught with problems. It requires a lot of knowledge and, given that much of cannabis growing knowledge is falls into the domain of "tribal knowledge" there are a lot of things that are passed as knowledge that have no basis in reality.

The second issue, and this goes back to the growers who control/influence the environment vs those who don't, is that it's "after the fact". It's impossible to read the plants and catch nutrient deficiencies as soon as they start to happen. It's only after there's a problem with the plant that a grower can start to diagnose the issue. At that point, since so many cases of nutrient imbalance are a direct result of VPD temperature and/or humidity being out of range, the first question to ask the grower is "What is your VPD what are your temperature and RH values?"

Take a grow that has been given way too much light because the grower just "dialed it up". If the grower catches it in, say the first hour, it's as simple as turning the light down a bit.

Underlying both of those issues is the idea of capturing metrics ( the dreaded "data" that one grower harped on me about in my last grow journal). Introducing data/metrics is one of the first things that any organization does to understand what going on. "If you can't measure it, you can't fix it." was one of the first lessons I was taught in my software engineering career (1990±) and it was an old phrase back then.

And that goes back to a point I raised earlier-some growers want to control/influence their environment and using VPD temperature and RH values is, frankly, the only way to do it. But if you're not interested in controlling/influencing your environment, it's perfectly understandable that having VPD temperature and RH data is of no value.

I understand that attitude completely. While I do like to control/influence the VPD temperature and RH in my tent, I'd much rather not have to futz with it. But the reality is, that for me and for my grow environment, I can't get the results that I want without controlling/influencing VPD temperature and RH.

All in all, if your grow environment is just really great or if you don't want to improve the outcome of your grows, controlling/influencing VPD temperature and RH is a distraction. On the other hand, if you don't have a great grow environment or if you want to get better results, it makes sense to use the tools that are available. And that choice is completely up to each grower.


The best source of explaining VPD that I've run across is from the folks at Pulse. They have a lot of good info and their PulseZero is $100± and is a very well engineered product (I retired a PulseOne but am using a PulseZero). The commodity priced Pulse products don't control devices and that's where the AC Infinity products shine. For about $80±, you can get a WiFi enabled controller that will control four devices according to how you set them up. For me, they not only help keep VPD temperature and RH in range but they save me a ton of time. We can earn more money, but we can't earn more time, right?

Oops - my timer went off. I upped my PPFD to 550µmol an hour ago and I need to see how the plants are doing.

Happy growing and may your VPD temperature and RH values always be in range!

 

[Chuckeye]

Day 25

More chop/chop

Apple Betty helped a lot, I managed to save two more fan leaves

Coco in fabric bags not quite keeping up...

Starting to look overfed ?

Water to run off every day ?

Cheers

 

[Sativa1970]

What are you seeing that makes you think they are over fed?

Don't want to water every day. Roots need to dry. Feeds O2 that keeps bacterial rot at bay. If the soil is dry every day you need a bigger pot. Those pots are good for up to another 4 foot.