Old Strains - New LED Light!

[Delps8]

For those who have had positive results using VPD, what calculator or chart did you use? What strain were you growing? Every calculator and chart seems to give different final values. 79.5F at 85RH has given a PVD of .49 to 1.45 on different calculators. Charts range around .8 to 1.2. Is there an offset range to accommodate for the needs of arid vs tropical strains?

I just look for the strains ancestral origin and then replicate the natural climate conditions. Generally this puts me around 30RH over the average recommended PVD with equatorial strains. F/RH; 80/80 seedlings, 80/75 veg, 75/70 flower. Reducing RH causes the plants to stop praying and wilt. Just curious if anyone has further insight into this.

VPD is nothing more than one number that covers a range of temperature and RH values. It's like the "feels like" temperature for human beings.

The reason for it describing a range of temperature and RH values is because it's measurement of the difference in vapor (water) pressure between the plant and the atmosphere. In plant terms, that's "transpiration".

If the temp is 77 and the RH is 62 that's a VPD of 1.0. A plant in veg will transpire "normally" at that temp+RH (VPD). If the temp is 64 and RH is 62 that's "cold and clammy" to a human and, if you check the chart, the vapor pressure deficit is lower at 0.64 because it's not as warm as before (77°).

Take that same 77° room and run a dehumidifier full throttle and the RH will get down to, say, 34%. That's the same temperature as before but the RH is waaay down so the plant will give off more water/transpire more.

That's all that VPD is about. If your VPD is high, you're going to need to water more because your plants are transpiring more. The issue is that if you don't adjust the strength of your nutrients, you're going to get more nutes in your plants than they can handle.

If VPD is too low, that's increases the chances of getting disease in your grow.

 

[Sativa1970]

I understand pressure gradients, what and how VPD works. All plant bio chemistry functions on pressure gradients. My question was why is it, that the charts and calculators, have so much variation, from one to another. I know that there are different charts for different stages of growth. Plugging the same temp, RH and stage into several calculators or charts tends to yield different results. Calculators do seem to be far less accurate. This is just the first chart from a google search result. Notice they don't exactly match. 75F 60RH is a perfect VPD 1 on your veg chart but that would be a 1.19 on this chart. Perfect for late flower. Good science is repeatable. Why isn't this repeating?

 

[Delps8]

I understand pressure gradients, what and how VPD works. All plant bio chemistry functions on pressure gradients. My question was why is it, that the charts and calculators, have so much variation, from one to another. I know that there are different charts for different stages of growth. Plugging the same temp, RH and stage into several calculators or charts tends to yield different results. Calculators do seem to be far less accurate. This is just the first chart from a google search result. Notice they don't exactly match. 75F 60RH is a perfect VPD 1 on your veg chart but that would be a 1.19 on this chart. Perfect for late flower. Good science is repeatable. Why isn't this repeating?

Good catch!

The only variable should be the leaf temperature offset. The Excel spreadsheet from Pulse Grow allows you to change that value.

[time passes]

When I change the leaf temperature offset to 0 in the Pulse document, the values match and drives home the point that a VPD chart should allow you to enter leaf temperature offset.

It's good that you brought that up. In most of my grows, the offset has been -2° F but for my last grow, where I had a lot of fans and a windspeed of 2 meters/second, it was -4.

I measured wind speed using an anemometer from Uni-T, the same company that makes the popular lux meter. I haven't seen a wind speed number in some time but I think 2 m/second is that value that was advised for growing in a commercial grow. Does that sound about right?

Anyway, when I had that much wind in the tent, the leaves were always rustling which is another piece of conventional wisdom that I think I heard when I started growing. Does that advice ring a bell with you?

 

[Chuckeye]

Ah, so you can factor leaf temperature IN place of ambient !

Thay may explain the differences in charts...

But I am not buying another gadget

Cheers

 

[Chuckeye]

Late in day 18 and The Girls are in their final homes

And three or four days later than necessary

Actually had the start of green algae growing on the insides, never seen that before !

Even the five days younger Hawaiian Snow had roots down the outside and circling the bottom of the solo cup !

Under HID I usually transplant anywhere from 18 - 21 days And Do Not have this much thick root growth !

Another bonus for LED, eh ?

The pails and bags had been sitting filled for days so the medium was dry.

I poured in a gallon from the top for the pails, no run off. So I put about a half gallon down the fill tube.

Came up to two drops on the gauge. I'll wait until the reservoir is empty and then give them a half gallon.

I'll continue to top them up to that level daily until they drink that in a day then I will start to fill the reservoir.

For the coco bags I poured in a gallon from the top. About a 1/4 gallon drained out so I left the bags sitting in that.

Not quite five hours later and they have almost wicked it all up !

Tomorrow I'll put them back on elevators. Still debating on whether or not to sit them on a perlite/reservoir/pan..

Ideally I don't want to have to water more than once a day ? Not a problem with ProMix HP.....

Light is @ 28", 30,000 lux in the center, 26,000 on the edges. 480/390 par. Temp is 80, rh of 54%.

Feed is 2.5g/gallon of Mega Crop one part.

Still have two droopy girls but their roots were fabulous

Cheers

 

[Sativa1970]

LED do tend to grow bushier plants and the roots are generally a mirror of the branches. I was using drain to waste when I switched to LED so I couldn't get a really good comparisons in root structure. Transplanting and after harvest the root ball did appear bigger.

Wasn't trying to go off topic with the PVD discussion. Just appeared to be a mystery variable. Wind speed makes perfect sense. Rarely quantified, but a minor change in air speed would have a significant effect on evaporation. Why everyone's chart is a bit different.

Wet hands in still air, vs waving your hands, vs a blower hand drier has a huge effect on drying time. I have a lot of air movement in my rooms. Three 16 inch oscillating and one 24 inch fan for three flowering plants. Would explain why they like higher humidity. Thanks @Delps8 and everyone else who helped answer this anomaly.

 

[Ke0ncp]

Nice all caught up and ready for the show!!

And I see we are in for more trippy Mylar

 

[Chuckeye]

LED do tend to grow bushier plants and the roots are generally a mirror of the branches. I was using drain to waste when I switched to LED so I couldn't get a really good comparisons in root structure. Transplanting and after harvest the root ball did appear bigger.

I'm starting to think I won't have any issues with height

But training these shorties will be interesting !

Wasn't trying to go off topic with the PVD discussion. Just appeared to be a mystery variable. Wind speed makes perfect sense. Rarely quantified, but a minor change in air speed would have a significant effect on evaporation. Why everyone's chart is a bit different.

Not really off topic and definitely interesting !

As a budget grower I don't have much control. When my rh is in the 30's I run a humidifier. Usually by late veg/early flower I don't bother.

But VPD is grow related, switching from HID to LED I'm paying much more attention to the little details and doing the best I can with the equipment I have. So far my numbers are Perfect, at lights off

Wet hands in still air, vs waving your hands, vs a blower hand drier has a huge effect on drying time. I have a lot of air movement in my rooms. Three 16 inch oscillating and one 24 inch fan for three flowering plants. Would explain why they like higher humidity. Thanks @Delps8 and everyone else who helped answer this anomaly.

My thanks also, had to be a reason, eh ?

Cheers

 

[Chuckeye]

Nice all caught up and ready for the show!!

And the show is starting to move along

My two droopy girls are looking much better just before lights on today

Could be they were just root bound

And I see we are in for more trippy Mylar

Still tin foil

Good to have you along for the ride, eh ?

Cheers

 

[Chuckeye]

Day 19

One day after transplant, not so droopy Now

Acapulco Gold

NYC Diesel

The Girls, standard rotate each day. Light spread isn't That Even

Cheers

 

[Chuckeye]

Day 20, two days after transplant !

The Maui Wowie and the Acapulco Gold are now in a race with the Columbian Gold for Perkiest

From the pictures it is now obvious the two were also hungry

Not sure how much that contributed to the droop ?

I precharged all with 2.6g/gallon of Mega Crop one part before transplant. The SIP reservoirs were empty tonight so they got a half gallon @3g/gallon.

The coco fabric bags took about 1/3 gallon to run off !

Maui Wowie

Acapulco Gold

The Girls

Won't be long before I can start training

Cheers

 

[Sativa1970]

Good looking, healthy, husky plants.

 

[Northward]

Day 20, two days after transplant !

The Maui Wowie and the Acapulco Gold are now in a race with the Columbian Gold for Perkiest

From the pictures it is now obvious the two were also hungry

Not sure how much that contributed to the droop ?

I precharged all with 2.6g/gallon of Mega Crop one part before transplant. The SIP reservoirs were empty tonight so they got a half gallon @3g/gallon.

The coco fabric bags took about 1/3 gallon to run off !

Maui Wowie

Acapulco Gold

The Girls

Won't be long before I can start training

Cheers

Maui wowie is one of my favorites! Looks great

 

[Chuckeye]

Good looking, healthy, husky plants.

LOL, I've been called husky before but never my plants

Maui wowie is one of my favorites! Looks great

That is the one I'm most looking forward to trying

Cheers

 

[Delps8]

Ah, so you can factor leaf temperature IN place of ambient !

Thay may explain the differences in charts...

Yes. The vapor pressure deficit is the different in vapor (water) pressure between the air in the tent and the vapor pressure in leaf. The vapor pressure in the air is a function of the air temperature and the RH. The vapor pressure in the plant is calculate from the RH in the leaf (100%) and the temperature of the leaf.

A VPD chart should allow you to enter the difference between ambient and leaf surface. If there's no way to enter the difference (called the "offset") it's not 100% accurate.

When you're using a device that's used with VPD, there will be a field in the "settings" where you can enter it.

But I am not buying another gadget

Cheers

I understand that completely.

 

[Jon]

Day 20, two days after transplant !

The Maui Wowie and the Acapulco Gold are now in a race with the Columbian Gold for Perkiest

From the pictures it is now obvious the two were also hungry

Not sure how much that contributed to the droop ?

I precharged all with 2.6g/gallon of Mega Crop one part before transplant. The SIP reservoirs were empty tonight so they got a half gallon @3g/gallon.

The coco fabric bags took about 1/3 gallon to run off !

Maui Wowie

Acapulco Gold

The Girls

Won't be long before I can start training

Cheers

Wow. Impressive. I was hoping they’d perk up for you after uppot. Very nice. You happy now?

 

[Chuckeye]

Wow. Impressive. I was hoping they’d perk up for you after uppot. Very nice. You happy now?

Thanks @Jon !

Very happy

Finally seeing some vertical growth !

And the two droopy girls are growing out of their purple stems, whatever that means ?

But still short enough I'm thinking I'll wait for six nodes before I top and remove all but the fifth and fourth nodes. Ideally I like to have the plant at 8 - 10" tall when I start horizontal training !

Except for the Mau Wowie, she's got some height. Was looking at her last night and I think I'll do my normal top above the forth node !

Might have bit off more than I can chew but I'm confident the new light can handle it

Cheers

 

[Chuckeye]

Day 22, two and a half hours after lights on

Cheers

 

[Delps8]

Day 22, two and a half hours after lights on

Cheers

Beautiful!

 

[Jon]

Day 22, two and a half hours after lights on

Cheers

Damn those are looking sweeter by the day. Totally loving the color you got going on and as I’m learning, you are maintaining turgidity. As also evidenced by your lack of complaint about drooping leaves now. Lmao! Wow. Looks like you got a rouge giant hybrid looking type something in the back middle. I’m guessing that one and the lower right hand plant are the two monsters.