LED and Calmag issues.

Yeah, you can use far-red also in veg and because of the lower intensity you would see the improvements pretty fast cuz the emerson effect is stronger with low light conditions. I also use far-red from the 2nd half of the flowering stage for the 2nd half of the day. Far-red has a few more useful effects and each grower should have some far-red on a separated circuit.

I know the heat wave bulbs but have not used them. Their heat waves are above 1000nm, probably 1000-3000nm or so. They would help to heat up the leaves which means you could work with lower ambient temps. Lower ambient temps means you need less humidity so it would help indeed to maintain a good VPD but you need to test it and measure the actual leaf temps with and without these bulbs. There are a few questions you would need to figure out. For instance...
How much watts are needed to increase the leaf temps by 1, 2 lr 3°?
How much space can be heated up properly with one bulb?
Can you avoid using a humidifier?
Power costs per day?
An finally can you improve your yields?

Its probably cheaper to use a humidifier running a few times the day as to use a few of such heat radiators all day long.

Heat waves also increase stem elongation like far-red. For this reason I don't use far-red in the first half of the flowering cycle unless its a low stretching indika and I want to see more stretch.

Currently I'm using 325w white LED, a mix of ⅔ 3k/CRI80 strips and ⅓ 3k/CRI93 COB's and have only additional 10w of far-red. My area is 10sft and I have around 20μMol/s/m² far-red from the CRI80 and 90 mix and another 20 out of the extra far-red diodes, maybe a little more. So 40, maybe 45μMol/s/m² total. That's around 5% of the total intensity and already enoung. Probably comparable to a CRI90 only spectrum and I simply don't need more cuz I can regularily shorten the flowering cycles by at least a week without loss in yield.

charsi420 said:

Been using Calmag @ 5ml/g during veg and currently in week 3 fl at 2.5ml/g. Problem is that my bottle of Calmag is about to finish and the new one is en route but delayed. I have enough for another 3 days (2G per day) and the bottle in transit will take a week to get here.

What's would be the best approach to use the remaining 15ml? I think my cation exchange is already messed up as I'd reduced the dosage to 2.5ml/g for a week during veg after observing some minor clawing. Run-off since then has always been lower than what I put in, even after restoring it to 5ml/g.

Click to expand...

If your girls have finished to grow and stretch out you can reduce the dose by 50-66%. The magnesium demand is higher as long the plants grow and develope new green mass. You can also use epsom salt to increase the magnesium content unless you need the additional nitrogene. Instead of ordering bottled calmag I would just order powdered calcinit (calcium nitrate ) next time.
It's cheaper, lasts longer and is of better quality.

Did you know Master Blend? Its a 3 part powerdered US fertilizer containing epsom salt, calcinit and an NPK 4-18-38 part containing all other neccessary micro and macro nutes. Pretty cheap stuff(15$/2 pounds) and has a pretty good formula for tomatoes and MJ. (Keep calcinit and epsom salt separated and mix it separated with some water before you add it to the final nute soup)

You could still use other additives like kelp, humidic acids and such stuff cuz its not included in the formula. If you want such stuffs included you could use for instance MegaCrop from Greenleafnutrients.

Randomblame said:

If your girls have finished to grow and stretch out you can reduce the dose by 50-66%. The magnesium demand is higher as long the plants grow and develope new green mass. You can also use epsom salt to increase the magnesium content unless you need the additional nitrogene. Instead of ordering bottled calmag I would just order powdered calcinit (calcium nitrate ) next time.
It's cheaper, lasts longer and is of better quality.

Did you know Master Blend? Its a 3 part powerdered US fertilizer containing epsom salt, calcinit and an NPK 4-18-38 part containing all other neccessary micro and macro nutes. Pretty cheap stuff(15$/2 pounds) and has a pretty good formula for tomatoes and MJ. (Keep calcinit and epsom salt separated and mix it separated with some water before you add it to the final nute soup)

You could still use other additives like kelp, humidic acids and such stuff cuz its not included in the formula. If you want such stuffs included you could use for instance MegaCrop from Greenleafnutrients.

Click to expand...

Thank you!

Yes, the stretch is over.

I did read a bit about using powdered Es and calcinit but couldn't/can't find reliable dosing information for all stages of growth. How much would I need of each per gallon and do I keep the order the same - Silica -> Es and calcinit -> M -> G -> B?

No "Masterblend" but I do see a 4-18-38 mix available, $3 for 500gms. So the 4-18-38, Es and calcinit is all one needs?

Do I calculate VPD based on ambient or leaf surface temperature?

My ambient is 77, but leaf temp is only 70. Should my RH be 56% or 22%?
2nd week flower.

Actually you need both, ambient + LST and humidity.

Redraw the chart with your LST - http://opennlabs.com/vpd/VPD_calculator.php

With LED..., by increasing ambient what exactly is that correcting? LST? So increase LST at the detriment of VPD? Because when you increase ambient you have to add additional water to the air just to maintain RH, ontop of the SVP increase, so increasing ambient definitely isn't helping with the VPD battle.

There must be a threshold of LST that once engaged, VPD has less of an effect??

2 plants with the exact same VPD will react differently when the LST > or < the ambient. Plant 1 with θ VPD but LST 3° under ambient VS plant 2 with same θ VPD but LST 3° greater...

Hmmm Seems plugging in the above into a VPD chart would give identical scenarios, that can't be right??.. I wonder how much SPD has to do with it... ? I wonder what the LST to VPD with respect to growing success graph looks like..

ChiefRunningPhist said:

With LED..., by increasing ambient what exactly is that correcting? LST? So increae LST at the detriment of VPD? Because when you increase ambient you have to add additional water to the air just to maintain RH, ontop of the SVP increase, so increasing ambient definitely isn't helping with the VPD battle.

There must be a threshold of LST that once engaged, VPD has less of an effect??

Click to expand...

Part of the problem I seeing now running both LED's and DE HPS is I'm not seeing very much of a difference in leaf temps between the 2 when checked or even much of a difference between ambient and leaf surface temps. Granted my HPS is kept farther away than the LED's but still their only 1-2 degrees F difference.

I wonder if its just more or less maintaining proper metabolic temps than anything?..

That when LED guys increase their ambient to get their plants metabolizing correctly that they kill their RH (temp went up) and that's why we're adding so much RH with LED. That it really has to do with LST more than anything? That we are essentially creating our VPD issue because we are trying to solve the initial LST problem (maybe SPD has to do with it?)? Seems you could solve the VPD problem by increasing RH... or... you could solve the LST problem (or SPD or whatever it is) and not create the VPD issue to begin with???

jarvild said:

Part of the problem I seeing now running both LED's and DE HPS is I'm not seeing very much of a difference in leaf temps between the 2 when checked or even much of a difference between ambient and leaf surface temps. Granted my HPS is kept farther away than the LED's but still their only 1-2 degrees F difference.

Click to expand...

Have you noticed any RH differences?

ChiefRunningPhist said:

With LED..., by increasing ambient what exactly is that correcting? LST? So increase LST at the detriment of VPD? Because when you increase ambient you have to add additional water to the air just to maintain RH, ontop of the SVP increase, so increasing ambient definitely isn't helping with the VPD battle.

There must be a threshold of LST that once engaged, VPD has less of an effect??

Click to expand...

What I'm seeing is that ambient matters to a degree, not as much as LST or humidity. You don't have to raise ambient to raise LST. The light will do it, even though it doesn't measure that way.

Example. 75 degrees ambient I need to have around 76-78 LST. Where the change comes into play at this point is in the humidity. If I have 30%, my plants will suffer. If I have 50-60%, they do much better, no signs of tox or def.

Now, if my ambient is 75, and my LST is less, that means my humidity is low, that's the only time I've encountered a lower LST than ambient.

What I have concluded is that when the LST is slightly above ambient, photosynthesis and nutrient pickup is good, thanks to humidity.

If that humidity drops, so does the LST. Only reason I can figure it does that is because excess transpiration or improper photosynthesis? I've narrowed it down to the 2 or maybe it's a combo of the 2.

All I know, is they are unhappy when humidity is low, even more so than when temps are low.

3rd Monkey said:

What I'm seeing is that ambient matters to a degree, not as much as LST or humidity. You don't have to raise ambient to raise LST. The light will do it, even though it doesn't measure that way.

Example. 75 degrees ambient I need to have around 76-78 LST. Where the change comes into play at this point is in the humidity. If I have 30%, my plants will suffer. If I have 50-60%, they do much better, no signs of tox or def.

Now, if my ambient is 75, and my LST is less, that means my humidity is low, that's the only time I've encountered a lower LST than ambient.

What I have concluded is that when the LST is slightly above ambient, photosynthesis and nutrient pickup is good, thanks to humidity.

If that humidity drops, so does the LST. Only reason I can figure it does that is because excess transpiration or improper photosynthesis? I've narrowed it down to the 2 or maybe it's a combo of the 2.

All I know, is they are unhappy when humidity is low, even more so than when temps are low.

Click to expand...

I think you may be on to something there. Maybe the inc in RH or increased water in the air does a better job of transferring the thermal from the light to the plant. It wouldnt make sense that your plant is transpiring too much at that time, considering the low RH, or would you not go that far?

ChiefRunningPhist said:

I think you may be on to something there. Maybe the inc in RH or increased water in the air does a better job of transferring the thermal from the light to the plant. It wouldnt make sense that your plant is transpiring too much at that time, considering the low RH, or would you not go that far?

Click to expand...

I don't know. How much can a plant transpire? Enough to affect humidity to what degree?

It's around 20% outside the tent. Without adding humidity, the plants keep it around 30-35%. That's still not enough. The leaves stay at attention but will droop by the end of the light cycle if the humidity stays low. If the humidity is good, no droop.

So, what I'm thinking, is that the plants are transpiring hard, overworking themselves, and that's why the droop. If they can keep humidity 10-15% higher than what they draw in, maybe that's working them that hard already. I wouldn't know how to measure it honestly.

http://opennlabs.com/vpd/VPD_calculator.php

^^^ When I plugged in a (+2°) LST & a (-2°) LST, I did get different readings.

(-2°C) LST - cooler leaf...
80°f @ 50% RH = 1.39

(+2°C) LST - hotter leaf...
80°f @ 50% RH = 2.04

According to the charts, the higher the LST over ambient, the greater the VPD danger.



I think MJ needs a certain LST as well as a healthy RH, ... just like all plants. I think after that the biggest issues are nutes & SPD. There are many areas that grow MJ outdoors with lower than 45% RH and temps over 85°f, and it thrives. I know this from experience. I think if SPD is tailored differently that we will see fewer threads and questions about "LED deficiency." I'm not disregarding VPD, but rather think there's more at play than what's being given credit. That's only my hypothesis though. I'm not trying to say its fact or more right than anyone else's. I think I was a wrong once, but it was so long ago that I can't remember - HA! good luck everybody!

[

Randomblame said:

Yeah, you can use far-red also in veg and because of the lower intensity you would see the improvements pretty fast cuz the emerson effect is stronger with low light conditions. I also use far-red from the 2nd half of the flowering stage for the 2nd half of the day. Far-red has a few more useful effects and each grower should have some far-red on a separated circuit.

I know the heat wave bulbs but have not used them. Their heat waves are above 1000nm, probably 1000-3000nm or so. They would help to heat up the leaves which means you could work with lower ambient temps. Lower ambient temps means you need less humidity so it would help indeed to maintain a good VPD but you need to test it and measure the actual leaf temps with and without these bulbs. There are a few questions you would need to figure out. For instance...
How much watts are needed to increase the leaf temps by 1, 2 lr 3°?
How much space can be heated up properly with one bulb?
Can you avoid using a humidifier?
Power costs per day?
An finally can you improve your yields?

Its probably cheaper to use a humidifier running a few times the day as to use a few of such heat radiators all day long.

Heat waves also increase stem elongation like far-red. For this reason I don't use far-red in the first half of the flowering cycle unless its a low stretching indika and I want to see more stretch.

Currently I'm using 325w white LED, a mix of ⅔ 3k/CRI80 strips and ⅓ 3k/CRI93 COB's and have only additional 10w of far-red. My area is 10sft and I have around 20μMol/s/m² far-red from the CRI80 and 90 mix and another 20 out of the extra far-red diodes, maybe a little more. So 40, maybe 45μMol/s/m² total. That's around 5% of the total intensity and already enoung. Probably comparable to a CRI90 only spectrum and I simply don't need more cuz I can regularily shorten the flowering cycles by at least a week without loss in yield.

Click to expand...

I Have found this interesting article that maybe explains the relationship between far red, stomata aperture and VPD...aparently plants can detect the wáter content of the air cause it affects the far red light transmision and not the red light transmisión.. hence..the plant throught the phytocrome can detect humidity changes….and regulate stomata aperture…At the end...low humidity conditions transmite more far red ..much more...so the plant can detect incoming drough..and close stomata decreasing transpiration…..

With our White leds lacking enought far red ..maybe a little the ones at 90 CRI but not very much...if we have low humidity...the plant does not receive enough far red and keeps transpiring as crazy...and eating nutes as crazy…Also if this happen in veg and we are using lot of blues and UVA that open the stomata...and problems increase. If we raise humidity and correct VPD values… or lower nutes concentration and reduce blue light intensity probably problem is solved...but we dont let the plant use its own moiusture sensor....So I think some kind of far red is needed….

Very interesting article…[email protected] think you have read this… if not, you would like it a lot.. maybe has been posted before

http://www.international-agrophysics.org/pdf-104140-35208?filename=Atmospheric moisture.pdf

I just re-read the thread.

In summary..

We have VPD issues with LED because we inc ambient as a means of inc LST, and due to this we have to add RH because the VPD is then out of alignment.

^^^ That makes sense.

I guess Id call that an SPD issue, not a VPD issue, but ultimately think this is where the disconnect is coming from. I've been saying that the added focus to VPD is a band-aid of a different issue, or a band-aid for poor SPD. After reading some of the older posts I see that was said a few times back by people that I misinterpreted as contradicting my comments.

I think the plant is reacting to the longer WV in a way that can't be totally mimicked with environmental control. And that this is the reason there seems to be inconsistencies in the correlation of environmental factors on VPD, compared to the selected timing of prioritized VPD mgmt.

3rd Monkey said:

What I have concluded is that when the LST is slightly above ambient, photosynthesis and nutrient pickup is good, thanks to humidity.

Click to expand...

Is it even possible to have a higher temperature on the leaves than ambient?

I can imagine that when lights just flip on that the leaves might absorb warmth faster then the speed of which the air can warm up.
But after a few hours when everything is evened out I would think the ambient temperature would always be higher or at least the same as the leaftemperature.
Or is it because the mass of the leaves absorb more heat and radiation and the air does not?
I also ask because most charts always give an example of a LST that is lower then ambient temperature.
quite complicated for me

Keesje said:

Or is it because the mass of the leaves absorb more heat and radiation and the air does not?

Click to expand...

Yep.

If there's EM radiation being emmited (not much IR in LED) it will effect air much less than whatever it's "shined" on, ie leaves. When you exhaust your area you cool your ambient but you can't pick all your leaves off every minute they are stuck there, they continually absorb energy regardless of air temp. EM travels though a vacuum. Convection is dependent on physical contact. If your LST is lower than ambient, it means your leaves are full of water and/or you're lacking IR.

Did anybody take into account that DLI might have some effect ?

jarvild said:

Did anybody take into account that DLI might have some effect ?

Click to expand...

I was under the impression the cannabis can't get too much light in veg. It might be something that is effecting my tomatoes, maybe.

3rd Monkey said:

I was under the impression the cannabis can't get too much light in veg. It might be something that is effecting my tomatoes, maybe.

Click to expand...

Why do outdoor and greenhouses use shade cloth during summers ? And yet they are lucky to get 16 hours of light at the summer solstice while we try to run 18+ for veg.