VPD - yeah it maters

[Three Berries]

My flower room is a closet with bifold doors. Hard to keep sealed. It has air draw in from the other side of the wall. I'm running a mister blowing into that air intake. I took two HPS lights out as they were driving the heat too high and humidity couldn't keep up. Does alright with LEDs but the temp is gets to the low 70fs.

I think I'm going to get a tent that fits in there. AC Infinity makes one that is 2x4x6 foot.

 

[Three Berries]

I got my tent the other day and set it up . Last night was the first run and the VPD was easy to maintain with just the mister mister I have. Only used about half the tank vs nearly the whole thing. Temps just above house temp around 70F.

 

[Gry]

So I always wondered about the VPD at night. My thinking was it didn't matter as the light input wasn't there. Not the case according to this study. I usually don't worry about the high humidity when the lights are off, limiting it to 80%. I guess I'm better with some constant or better ventilation when the lights are off. Currently my seedlings in the tent are at 80%/64F just before the lights come on. The only ventilation I've been using is natural through 6" elbows just two small plants.

Another vote for the AC Infinity Cloudline's with the humidity sensor!

Night-Time Transpiration – Favouring Growth?
https://www.cell.com/trends/plant-science/pdf/S1360-1385(19)30022-6.pdf

Highlights

Plants loose water at significant rates during the night through ‘night-time transpiration’.
Night-time transpirational water loss is most likely the consequence of having respiratory CO[SUB]2[/SUB] escape at sufficiently high rates through stomata.
As night-time respiration fuels growth and depends on daytime provision of storage carbohydrates, there must exist some regulation, involving the internal clock, between daytime photosynthesis and growth, and night-time transpiration and growth.
Night-time growth presents a more efficient use of taken up water for leaf cell expansive growth compared with daytime growth, and could represent an overlooked stress acclimation process.Plants grow and transpire water during the day and night. Recent work highlights the idea that night-time transpirational water loss is a consequence of allowing respiratory CO[SUB]2[/SUB] to escape at sufficiently high rates through stomata. Respiration fuels night-time leaf expansion and requires carbohydrates produced during the day. As carbohydrate availability and growth are under the control of the plants’ internal clock, so is night-time transpiration. The cost of night-time transpiration is that water is lost without carbon being gained, the benefit is a higher efficiency of taken up water for use in leaf expansion. This could provide a stress acclimation process.

Would like to see one of the sensor units one could use for any of the fans.

 

[Three Berries]

Would like to see one of the sensor units one could use for any of the fans.

Inkbird makes some good products.

https://inkbird.com/products/itc-608t

 

[Gry]

My flower room is a closet with bifold doors. Hard to keep sealed. It has air draw in from the other side of the wall. I'm running a mister blowing into that air intake. I took two HPS lights out as they were driving the heat too high and humidity couldn't keep up. Does alright with LEDs but the temp is gets to the low 70fs.

I think I'm going to get a tent that fits in there. AC Infinity makes one that is 2x4x6 foot.

I use a closet that has a set of French doors that is sounds like it may be similar.
Made a frame of one by ones the size of one of the doors, and then cut a sheet of plywood to fit that opening.
In the bottom I cut an opening to accommodate a regular home AC filter. Run the 6 inch exhaust fan through
a hole cut in the top of the insert.
Like the idea of a decent controller, that can used with replaceable fans.

 

[Klompen]

If you are growing organic, mulch really helps immensely when it comes to regulating water loss. My plants tend to get a little ripply but otherwise veg just fine. Flower is more of an issue. These cold temps and relatively dry air don't make my flowering girls happy.

 

[SoSincere]

Hi can I ask you something? So praying leaves is NOT god as said I have read by a lot of other people that Praying Leaves are Happy plants... Is that wrong?

In my experience, you want them slightly praying a bit in flower, and keep them level in vegetative

 

[flylowgethigh]

So I always wondered about the VPD at night. My thinking was it didn't matter as the light input wasn't there. Not the case according to this study. I usually don't worry about the high humidity when the lights are off, limiting it to 80%. I guess I'm better with some constant or better ventilation when the lights are off. Currently my seedlings in the tent are at 80%/64F just before the lights come on. The only ventilation I've been using is natural through 6" elbows just two small plants.

Another vote for the AC Infinity Cloudline's with the humidity sensor!

Night-Time Transpiration – Favouring Growth?
https://www.cell.com/trends/plant-science/pdf/S1360-1385(19)30022-6.pdf

Highlights

Plants loose water at significant rates during the night through ‘night-time transpiration’.
Night-time transpirational water loss is most likely the consequence of having respiratory CO[SUB]2[/SUB] escape at sufficiently high rates through stomata.
As night-time respiration fuels growth and depends on daytime provision of storage carbohydrates, there must exist some regulation, involving the internal clock, between daytime photosynthesis and growth, and night-time transpiration and growth.
Night-time growth presents a more efficient use of taken up water for leaf cell expansive growth compared with daytime growth, and could represent an overlooked stress acclimation process.Plants grow and transpire water during the day and night. Recent work highlights the idea that night-time transpirational water loss is a consequence of allowing respiratory CO[SUB]2[/SUB] to escape at sufficiently high rates through stomata. Respiration fuels night-time leaf expansion and requires carbohydrates produced during the day. As carbohydrate availability and growth are under the control of the plants’ internal clock, so is night-time transpiration. The cost of night-time transpiration is that water is lost without carbon being gained, the benefit is a higher efficiency of taken up water for use in leaf expansion. This could provide a stress acclimation process.

I have read that a couple of times and have some fundamental questions. Any help is appreciated, as I am starting to actually try to control the environment in the tents properly. It is a hassle in my lung room, which is also where I and the dawg spend a lot of time (wasted mostly). We need a decent environment also. I am thinking about a 'lung cabinet' to condition and filter the air fed into the tents.

I am doing what it takes with the airflow and light power to keep the flower-height temperature at or under 75*F with the lights on. The leafs are a couple degrees cooler. The VPD chart wants less humidity than the stuff I currently have can provide. I struggle to get much under 55% at the tops, but I am working on it.

At night the tent gets cooler, and I am not following the VPD curve for the stage of growth the plant is in. Because I can't. Yet.

Is the article above saying I will be making plant at night, and not making trics, as a result of the wetter environment??

Also reading the above, and remembering something about plants eating CO2 and making O2 in the daytime, and the reverse at night, I am confused. Are we trying to control that humidity when the temps cool, so the CO2 that gets eaten by day, is not released at night when the air is cooler? (because the humidity is too high)?

The VPD chart moves right, from higher to lower humidity, as the plant progresses. Is that to control the type of growth via the VPD, and make flower / trics instead of leaf, by reduced humidity?

Does this help explain why I make bushy plants that don't have many trics - from too much humidity at night, and the plants staying trapped in the veg mentality? And to add insult to injury, the article suggests also giving away the CO2 (trics) at night when the air is cooler but still humid?

So do I need to follow the VPD curve at night also? Can I do that by letting the tent stay 75* at night, and keep the humidity right for 75*? Would that defeat some purpose?

Seriously, I have no clue. Help 'splain this and maybe I can grow some frost someday.

 

[Three Berries]

I was watching a video by the Good Dr and he said trics need sunlight to be produced. So I don't know about that.

Plants use sugars stored in the root and plant tissue from the day before to keep it alive without light. The fact they do reverse gasses with sunlight should tell us the there is transpiration with lights out.

So what we need to find out is what do the plants do with the sugar they are metabolizing with lights out.

I worry more of the VPD numbers that temp, though I limit temp to lower 80Fs. Really depends as I find the plants can naturally provide a humidity level above what I want when all is working good, so exhausting for humidity controls the upper heat.

When I find the temp is getting too high and triggering the exhaust, this will bring down the humidity below optimum VPD, I add humidity. This is happening right now with the change in seasons.

Going from heat and high CO2 to AC this week with 5 days in upper 80Fs this week, a bit warmer house temps and a bit higher house humidity too.

When lights off I've just been worried about anything over 80% for mold and fungus reasons. It would be good to know if going to the hassle of keeping lights off VPD in range is worth the trouble.

An outside plant around me will see 100% humidity over night quite frequently dropping to 40% during the day.

 

[GMT]

"So what we need to find out is what do the plants do with the sugar they are metabolizing with lights out."

Might not be all that practically useful, but if you want to see:

 

[flylowgethigh]

I have read that a couple of times and have some fundamental questions. Any help is appreciated, as I am starting to actually try to control the environment in the tents properly. It is a hassle in my lung room, which is also where I and the dawg spend a lot of time (wasted mostly). We need a decent environment also. I am thinking about a 'lung cabinet' to condition and filter the air fed into the tents.

I am doing what it takes with the airflow and light power to keep the flower-height temperature at or under 75*F with the lights on. The leafs are a couple degrees cooler. The VPD chart wants less humidity than the stuff I currently have can provide. I struggle to get much under 55% at the tops, but I am working on it.

At night the tent gets cooler, and I am not following the VPD curve for the stage of growth the plant is in. Because I can't. Yet.

Is the article above saying I will be making plant at night, and not making trics, as a result of the wetter environment??

Also reading the above, and remembering something about plants eating CO2 and making O2 in the daytime, and the reverse at night, I am confused. Are we trying to control that humidity when the temps cool, so the CO2 that gets eaten by day, is not released at night when the air is cooler? (because the humidity is too high)?

The VPD chart moves right, from higher to lower humidity, as the plant progresses. Is that to control the type of growth via the VPD, and make flower / trics instead of leaf, by reduced humidity?

Does this help explain why I make bushy plants that don't have many trics - from too much humidity at night, and the plants staying trapped in the veg mentality? And to add insult to injury, the article suggests also giving away the CO2 (trics) at night when the air is cooler but still humid?

So do I need to follow the VPD curve at night also? Can I do that by letting the tent stay 75* at night, and keep the humidity right for 75*? Would that defeat some purpose?

Seriously, I have no clue. Help 'splain this and maybe I can grow some frost someday.

I have been running the night temps at 75* in the tent, and can get humidity down to 48. Working on it.

 

[f-e]

Yes VPD, but where?
I just completed another run working on a notion that seems to be playing out. I kept RH above the plants lower than that within them. Typically I pull air up through them, but decided to keep below the canopy fairly well sealed. I actually kept about 60-65% around the pots and lower areas, but 50% around the buds. The plants like that 60%+ and the buds were not at risk as the bigger one's were out on the drier conditions. I have not seen a wild grow, but figured it must be lower RH below them, even it there was no crowding.

I was thinking about Ca transport also, but my pillows calling

 

[Three Berries]

We are in summer hot and humid conditions this week. AC is on in the house but not really cranked so indoor humidity is 68% right now. The flower tent is struggling to keep it under 80% and the air going in is 74%. My intake is in the bathroom closet. I'm wondering if it's picking up humidity from the open toilet? No wet towels or anything around...... But then the veg room has a fan blowing air out towards the bath room door.

Poor veg tent has the door open and still 79%.

Just switched lights in all though so it's a new learning curve on the heat management.

 

[hazepadano]

Chiedo scusa... Mi sembra che state complicando il semplice!
vedo una gran moda di controlli maniacali del vpn.
nel mio giardino il vpn é la base.
Se fa caldo, nn abbasso la potenza dei watt, alzo l'umidità.
non ho centraline che mi controllano l'ambiente mi sembra molto semplice.
troppe complicazioni amici!

 

[Bio boy]

This is boss , my mg def is showing under led at 22c 55rh does anyone recommend the gas controller vpd etc ? How do you control your vpd

 

[plumsmooth]

LST Leaf Surface Temperature Too LOW! VPD acceptable at 55% Humidity 73 Degrees.

Problem if temp is that low under LED LST may be even Lower like 70. I believe if you can not raise temperature you need to lower Light Intensity i.e. Dimmer

This is boss , my mg def is showing under led at 22c 55rh does anyone recommend the gas controller vpd etc ? How do you control your vpd

 

[Terpyterps]

It is important but also you meet the requirements when you stay within the parameters that are loosely given for growers. In that sense you are not required to check that all the time if you know that you are within them. DLI in the other hand is something that you should be checking and that can actually help saving some electricity, maybe not significantly for one grower but if everyone does that it makes huge difference around the world and you are not stunting growth by too much or too little light. Because there is no point giving seedlings 800 umol/m2 because you could get away with way less and get better growth too. I have now some autos at flower stage and they are at 18/6 scheduled and they are getting around 900-1000 umol/m2 and below the canopy there is perfect condition for vegging plants so I take advantage of the weaker light and have some photoperiodic girls waiting for their turn. I have around