Factors that influence growth and development ( Temp and VPD)

[legalcanada]

to move them, i posted in the wrong thread originally to ask about VPD i didn’t see this thread before posting

Factors that influence growth and development ( Temp and VPD)

Temperature Plant growth and development is primarily influenced by temperatures at the growing points of plants (i.e., roots and shoot tips). When we are discussing temperature, it is important to understand that plant temperature (not air temperature) drives physiological responses in plants. Air temperature can differ by as much as 10° F from plant temperature, depending on your light source (HPS, MH, or LED), light intensity, humidity, and air speed. For example, HPS lights emit a large perc…

[MadScientist]

@legalcanada

to move them, i posted in the wrong thread originally to ask about VPD

Done good sire. Your wish is my command!

[Dewb]

vpd is vapor pressure deficit. vapor pressure is basically the relationship between temp and RH and the pressure it creates. vapor pressure deficit is the difference between the vapor pressure and the pressure the plant creates during transpiration.
think 2 forces pushing on each other.
so if your temp is high and RH is low there is less pressure in the air so the plant transpires faster.
and the opposite is true low temp and high RH slow transpiration in the plant.
ideal range is from .45 - 1.25 kPa with a target being .85 kPa, however most plants grow well between .8 and .95 kPa.

side note: it appears the chart i posted is not in kPa. apologies.

[legalcanada]

going off TTs chart above i’m around 1.45 in late veg but the plants seem to be doing OK

[Dewb]

Plants will do OK outside the vpd range, but staying within it or as close as possible you will see increased growth rates, more time between waterings, and a lot happier plants in general.

[Tinytuttle]

Like Dewb said earlier in the thread plants will do fine outside the range but for optimal growth the Vpd needs to be in the sweet spot. I queued in on your post section highlighted … so in following natures sign when coming in to flower ( your increasing temp part) in fall, temps are decreasing not increasing when keeping your 40-55 Rh and keeping it a little cooler conditions you’ll hit your sweet spot!

@legalcanada

the only way to bring it to the acceptable range would be raising my humidity to around 70-75 and actually keeping it there for the entire flowering … because i’ll be upping my wattage and increasing the temperature thru out flower … i

[legalcanada]

ok i’ve realized having an AC is unavoidable lol thanks for your help guys i’ll hit that sweet spot alright

[Dewb]

found this in my notes on vpd

here’s one for all the math people
needed:
ambient temp
relative humidity
canopy air temp

now the fun
to compute directly from temperature:
(do this for air temp and canopy temp)
vpsat = e^A/T+B+CT+DT^2+ET^2+FlnT
where
vpsat is saturation vapor pressure in kPa (kilopascal)
A = -1.88 x 10^4
B = -13.1
C = -1.5 x 10^-2
D = 8 x 10^-4
E = -1.69 x 10^-11
F = 6.456
T = temp of air in K (kelvin)

Temp in K = temp in C (celsius) + 273.15
Fahrenheit to celsius = ( F* - 32) x .5556

then we need the partial pressure of the vapor

vpair = vpsat x RH/100 (RH being relative humidity)

and finally the vapor pressure deficit which is the difference between our answers

vpsat - vpair = vpd
or if we have the canopy saturation (which why we did all that math for both air and canopy)
vpcanopy - vpair = vpd
(more accurate because we are looking for that balance between the pressure the plant creates and the pressure in the environment.)

[Kobracom420]

I was just trying to learn more about this…Thanks Dewb…

[Muleskinner]

I’ve uploaded the Fluence guide before, here’s the complete version

Fluence Bioengineering_High PPFD Cultivation Guide_v1.2.pdf (1.4 MB)

another good one! Lumigrow

LumiGrow_LED_Growers_Guide_for_Cannabis.pdf (2.0 MB)

and not to be outdone…Illumitex…we got 'em all here at OG!

Illumitex-Cannabis-Grower-Guide.v7.pdf (947.0 KB)

[Kobracom420]

Thank ye, thank ye.

Regards,

K

[cdnBuddy]

Lots to learn! I’ve read up on VPD, and I’m afraid to follow it. Mainly flowering stage scares me as the humidity would be around 60% at times.

Do I ignore all the information I’ve read that say to keep humidity between 40-50% in flowering and to even reduce that near the end below 40?

I’m planning on picking up a Pulse One, which monitors my grow room for my birthday this year and I’d like to learn as much about this before hand.

[Dewb]

Towards the end of flower we let the rh drop to around 40%and out of optimal vpd.

[pjay_dubya]

This is great! Radiant heat off lights AND the air flow “shape/pattern” in the room would give all kinds of different temps per square foot of space/various surfaces, floor, middle, ceiling, soil surface, canopy surface, left side of plant, right side, front, back… I guess a really good room minimizes that variance.

Same may be true of humidity depending on air flow too no?

I just started playing with an infrared thermometer too. They really show you so much more than a fixed-location thermometer does.

[Olbrannon]

@pjay_dubya

I just started playing with an infrared thermometer too. They really show you so much more than a fixed-location thermometer does.

Awesome tool. Used to use them for many different reasons. Looking for bad bearings. Checking product temps…just so many uses.

[cdnBuddy]

@Dewb

Towards the end of flower we let the rh drop to around 40%and out of optimal vpd.

Thanks!

Waiting for temp gun, so I can give it a go with my plants!

[Dewb]

Yes there are variances within rooms… you do what you can to minimize them… but as for vpd and environmental measurements in general you want to take your readings at canopy level…how the room feels to you doesn’t matter it’s how it feels to the plants that matters…

[Grapefruitroop]

Yo yo yo
Due to the fact that my second dehum is at the repair shop im having to run my sealed room with just one plus the a/c…
RH in middle late flower pretty high ranging from 59-69 at week 6 now… but with my temps im in perfect transpiration zone…
I generally add at the 4 week of flowerin another dehum to lower the range to the usual raccomended but if feel that both time i did it i messed up the armony that was in the room and i even made the mistake to overwater em to compensate the high transpiration stress…leaves were always kind of droopy but the buds were fattening nice so i didnt care much…
Now in high humidity but in vpd range the plants are always perky…from the morning till the bedtime…even right after watering…
Im gona keep it like that and see what happen…
I have a pretty tight and big canopy (about 25x5ft), at first glance seems very risky but i got also lots of fans and good circulation also under the canopy due to nice pruning…
I have a good feeling about it and ill keep RH that way…as soon as the dehum arrives ill set it on a timer to run just few hours when lights go off and acouple other times during night time to avoid RH spikes after waterings…but thats it
I hope ill make it safe to the harvest without molds! Send me good vibes! ill report back updates

[Grapefruitroop]

So…the humidity went down a little bit during the weeks just because i was watering with slightly less water than what i was recollecting…and i reached harvest with a range of 56-65
No molds no problems!

[Craigson15]

It is my belief that ‘root zone moisture level’ plays a huge part in how vigorous plants grow.

I say this because;
a) hook up blumats in a soilless grow like promix and watch the growth explode.
b) i plant same size clones in my notil bed and some explode w growth whike others lag behind. Yes, proximity to the lights make a diff too, but the biggest factor seems to be the rootzone moisture level.
Cheers