Take The Vpd Poll. How Important Is It?

[Douglas.C]

Lower temps and RH in late flower is one thing but in veg VPD does play a role in production of mass.

Yes, indeed it does, which is why I only mention flowering.

The point i'm trying to make is that the size of the cells don't change, you just have more cells. So it still comes down to the genetic potential of the strain.

Yes, and the trichomes have more distance between them, with the additional cells. Again, same genetics, much frostier looking in low temp/rh grows.

I grow in both cold and warm rooms, In fact I just harvested 4 plants in a max of 62 degrees and a RH between 20-30 %.

62F is too low for vigorous plant growth, 20-30% is too high of a humidity, for that low of a temp. Because of this, your transpiration rates are too low and it shows in the end product.

Your plants need transpiration, either through hydration or evaporative cooling. Most people go with moderate temps 75F-80F and moderate humidity 30%-40%.

If it's cold and not dry enough, you have very low transpiration. When it's hot and too dry, there's too much transpiration. Either way you slice it, quality suffers.

 

[MidwestToker]

80F is to hot for an indoor grow under hid's. My rooms max at 72, with lows at 65F.

 

[Gdub818]

i think it could def be a reason for newer growers to have major problems.if the rh gets too high they have one set of probs and when it gets real low they have totally dif probs.low rh will def make a new grower work hard to keep plants from locking out nutes or burning the piss out of them,even more so if they are following a feed chart lol.and i do think higher rh in the 60-75%range can make a shitty grower look much better.that is until the bugs and molds decide its a perfect spot to hang out when it creeps into the 80% range hahaha.but i cant say i ever saw a grower with problems post pics and say,oh fuck dude those plants are def not happy cause the vpd is off.then again most times new growers wont give all the important info needed to get proper help without being proded with multiple questions.

what would recommend for sfv og's for temperatures and rh during flowering week by week?

 

[sixstring]

what would recommend for sfv og's for temperatures and rh during flowering week by week?

The sfv og i ran a while back was happy in my room which is still always 40%rh or less but usually 40% and my temps used to be 78 to 80f lights on and 65 to 68f lights out but i keep those closer now.im having great luck at 76 to 78f on and 70f off still running 40% rh.
With that said,every garden is very different. I run peat based soil and feed every day both veg and bloom rooms.i also run veg at 78f and 30 to 40% rh and my veg lights run 17 on 7 off.but i also have my fixtures all timed 10 to 30 mins apart so it ramps up and down just like my flower room.i run 11 on 13 off in flower as well.but there are so many variations from grower to grower its hard for any of us to give anyone else advice imo.for first timers i would say 75f and 55% is a good place to be from day 1 through week 6 of flower, then drop rh to 35% to finish the plants off.those numbers should be easy enough for anyone to garden well and have good quality flowers.

 

[jaybodankly]

I try to put it all together for comparison,

 

[jaybodankly]

I see it as setting a temp and having a range of acceptable humidity.

 

[Ignignokt]

Lovely to see this debate continue to elicit responses from practical interpretations of the science and grower observations of results. I find it very useful to learn from all types (meaning I'm not a crop bigot) of agriculture practices. VPD is a well accepted measure in the greenhouse industry. Even though mixed light sourcing is complicated and not a great (exacting) model for artificial light/sealed room efforts, we can learn much from them. True, there is a different path for non-flowering plants, however I'd not dismiss VPD as only for lettuce farmers.

 

[sixstring]

I try to put it all together for comparison,

Those charts are quite different .im running pretty much at 22 between the two charts lol

 

[GT21]

Those charts are quite different .im running pretty much at 22 between the two charts lol

I prefer 15 or better in veg and flower.

 

[sixstring]

I prefer 15 or better in veg and flower.

Yeah but .....

Deuces seem to work fine fer me lol

 

[jaybodankly]

They are pretty similar charts. The red chart allows for a wider range of acceptable humidity at a given temperature range. The blue chart is a subset of the red chart. Be interesting to find the source of the charts and see what plants they were intended for.
I think we can all agree that we need some real cannabis science to answer these questions.

 

[Ignignokt]

I think it becomes clear that most are picking their median environment values to pick a spot on the charts. I would suggest that:

1. The environment of concern is the canopy - temperature measurement needs to occur THERE. I'd suggest non-contact remote sensing devices (cheap, available) The ambient room temperature is not even a good proxy - the type of light source is a factor. Some lamps project so much far IR on the canopy (that then dissipates to ambient) actual, measured VPD temp is well off any relative guess from the ambient room temp.

2. If you collect data 24 hours a day, you would find the VPD value shifts as the room (depending on size) "breathes". I've seen serious vapor dumps when CO2 is used to its best effect. While many are fairly low-tech, serious greenhouse installations have serious control equipment to manage the variables. You spot the trends before damage ( or delay ) sets in.

3. Typical median values are chosen because the VPD calculation (in real time) is difficult unless you have instrumentation. Remote temperature sensors are now fairly cheap - and there are many sorts of handheld digital sensors that are viable choices. Cheap humidity sensors degrade quickly and often have an error or 10% or more. Better silicon based sensors exist, however you don't find them in most consumer digital meters.

So, YMMV depending on your tools, as well.

 

[jaybodankly]

I use an infrared thermometer to set my room controller sensor placement till they match temp leaf temp.

 

[Ignignokt]

Yes, indeed it does, which is why I only mention flowering.

I've heard you on this point before Douglas, however I don't think this was meant to be flower stage specific. Indeed, a low moisture, cool fall environment is probably optimal for flower, color and even terpene production. Before you get to that stage, you have to build a sturdy foundation otherwise the stress of "fall" just brings out everything - mildew, mold and eventual substrate (soil or whateva) failure in indoor environments ( usually due to over feeding. Aren't the nutrient sales guys doing a great job? )
I think your points about end product are important. I just wonder if this is dogma for you.

 

[GT21]

Yeah but .....
View attachment 671988 View attachment 671989

Deuces seem to work fine fer me lol

When i said better i meant 15 or HIGHER hahaha

 

[Douglas.C]

I've heard you on this point before Douglas, however I don't think this was meant to be flower stage specific. Indeed, a low moisture, cool fall environment is probably optimal for flower, color and even terpene production. Before you get to that stage, you have to build a sturdy foundation otherwise the stress of "fall" just brings out everything - mildew, mold and eventual substrate (soil or whateva) failure in indoor environments ( usually due to over feeding. Aren't the nutrient sales guys doing a great job? )
I think your points about end product are important. I just wonder if this is dogma for you.

My observation... I use the same conditions for both veg and flower and I end up with short, stocky, healthy plants from veg. It's not so much dogma, as a condition of the climates I've lived in so far. I started with not being able to afford climate control (beyond temp) in very dry areas of the country and, due the quality differences noted, have continued to spend no money on raising humidity in later years. :)