This appears to be the scientific arguement against a 24/0 light/dark cycle for veg

[LJB]

I don't get why people keep needing some scientist to them how to grow... do some simple tests and you'll find out for yourself, that's what I did and now I know which works better.

Who said that they need scientists to "tell them how to grow"?

I certainly didn't, nor did I start growing that way. However, I'm finding it helpful to pick up on the accumulated knowledge from human history.

Crops and plants have been grown and studied by humans for a very long time.

We're not re-inventing the wheel here.

It's easy to do, take some clones from the same mother plant and put half in 24 light, and the others in 18 hour of light. I did this a few times and the ones that had a dark cycle always rooted faster and healthy.
Then I did the same test with rooted clones in soil. The clones in 18/6 roots grew faster and stronger. The plants were a bit slower, but only until the roots developed well.

That's great! But you're not at all curious, not in the slightest, to know why the roots of the plants grown under the 18/6 regime grew faster and stronger? Just knowing that they do is good enough for you? Nothing wrong that, just like nothing wrong with some of us being a bit more curious.

I purposefully put the words "scientific argument" in the thread title so that people wouldn't jump to the conclusion that all of their own non-laboratory experiences and observations have no merit, but apparently not even that was enough.

 

[LJB]

I think you all that are talking about 24 hours of sun in Alaska are ignoring one thing...

It's not only about continual light, it's about high and low levels of light.

Those plants in Alaska aren't getting noon sun, i.e. 2000 PPFD, 24 hours a day.

However, under constant moderate light (200 mmol per m2 per second photon flux density) and constant intercellular CO2 (28 Pa), the circadian rhythms still persist for several days with the same amplitude and period as under normal conditions (the curves in the previous graph).

Since photosynthesis is dependent on light energy, we might expect to see changes in circadian rhythm depending on the intensity of light. Under conditions of high light and high CO2, photosynthetic activity is very high. We can determine how such environmental conditions affect the circadian rhythm.

[..]

Under conditions of constant high light, the circadian rhythms in carbon assimilation and stomatal conductance quickly flatten out after a couple of days.

 

[Young Pumpkin]

Are there any "experiments" here? Someone MUST have done it already...grown a batch (clones) in 16/18/24 hours of light and compared them... Anyone have a link to it? I can't believe it hasn't been done...

I'm with ibjamming, if some one has a comparison I'd like to see it. I've been 24/24 for 30 years, since the days of "banks of 4 ft. flouro tubes". Just seems to me when I started more growth/light was why I went 24. Maybe its just me. Pics of going into flower would be helpful too since I wouldn't expect much, if any difference there.

I've had HIDs and the same clone/breed for the last 10 years. My friend who gave it to me tried other ways but he "Thought" 24 worked better. Also how quick does a person expect a plant to flower. After 12/12 starts where does flowering officially begin??? With all due respect to mother nature aren't we trying to manipulate "nature" all we can to our benefit??? From soil to hydro to nutes to CO2 to pulling males??? Screw natural, I want to up the ante, safely.

But Pete said it best, what ever works for you. Genetics may be part of it too??? Try it, post some pics, I'm all eyes an ears but will stick with 24 in my clone and veg room. If natural is what ya want go dump some seeds in a field and leave 'em alone. And no, nature does not make a hole 1-2 inches deep for each seed after they fall to the ground, lol. And from my experience 24 is easier on equipment. No initial, split second, power surge. "Nature Manipulation" is why I'm indoors. I'll stick to 24 on as the jury may still be out but not for me. Tho from a debate point it seems like this could be settled. Good Thread.

 

[LJB]

Mr. Mike, what's with the attitude?

if you've got something that contradicts what I've posted, than please come with it.

It's not about winning to me, it's about gathering the facts.

The thread title says, "this appears to be...."

I am totally clueless about the subject of autoflowers. If you both drop the attitude and the science, that would be much appreciated.

 

[LJB]

Conclusions: ...Changes in light intensity and carbon dioxide concentration can affect circadian rhythms of photosynthesis."

Oh, so the circadian rhythms can change according to light schedule and CO2? So these rhythms are "plastic" and plants seem to adapt, quite easily, such as Japanese hydroponic lettuce farms which out yield nature.

I thought it was clear that the author was distinguishing between constant high and low levels of light. No one said the rhythms aren't plastic and that plants can't adapt.

It's something I'm wondering about at this very moment - that is - what are the ideal levels of light, temp, humidity and CO2 that allow a more constant level of photosynthesis with fewer peaks and valleys. i.e., Is it possible to prevent the "noon break"?

There exists a small school of thought that says an 18 on / 14 off light schedule during flowering does that just for cannabis.

 

[GrowerGoneWild]

there are two areas of 24 hr light on our planet,above 60 north latitude and 60 south during the respective summer periods,i know everything grows like crazy in alaska during the summer,only takes a month after the last frost before the grasses are head high.

Agreed.

The research suggests that 24/0 is counterproductive, but your simple observation is true. There is a literal explosion of growth during those short months.

If the plant is adapted to the long light cycles, its not a problem. Lets look at ruderalis, closely related to the indica/sativa strains.
that stuff will flower no matter what.

 

[unclefishstick]

I wonder if that hold true for seeds that pop under 24/0?
There are plenty of weeds in the arctic that only see 20/4 - 24/0 their whole life cycle.
Are those plants all messed up? I was up there in 95 and can attest to the vigor
of plants growing in natural 24/0.

Jinx! Sorry UncleFishSticks, now you can't post until I say "Jinx" again. Oh damn.

Midnight sun is something that everyone should see atleast once in life! You have to go above arctic circle thou.
In middle of night sun is WAAYYY above horizon. Very psychedelic!
I usually try to spend summer solstice up there.

The reason plants grow very fast here is the very short summer.
At spring time after snow has melted, nature just explodes with shades of green!

the only thing that i noted during my time in alaska,i was only at 54 n latitude so we didnt have true 24 hr daylight only 22hrs and 50 odd minutes at solstice ,was that veggie garden plants would start to flower much quicker after the solstice.Basil,letuce,broccoli and the like would turn to seed quickly in august.the only outdoor or greenhouse pot i saw finished by the end of september

 

[*mistress*]

24/0 produce bigger plants in > time than 18/6, 19/5 20/4,21/3, etc...

tried them all... though 20/4 does make for nicely spaced internodes... 24/0 will get trees in 2 wks under 1k's 24/0...

18/6 just takes more wks & more centimeters between internodes...

recall that ea plant has own specific trigger for flowering... ideally, turn clock back 15-30 min per day, or 2-days, to find exact # of hrs for ea cultivar... can then run, say 14.5-8.5 & take advantage of more phtosynthesis energy to distribute in dark cycle...

12/12 ok, but really generic, especially if running multiple cuts... requires time, but can find exact hrs required for flowering... stop veg short of that & extend growth to max potential...

+++ to run same cuts over & over & over & do test on different light cycles...

19/5 generally provides nicely spaced internodes, but 20/4-22/2, w/ higher temps during the 2hrs of darks, create larger plants in same span... higher temps to have zero diff (pref 80*f day+night)... temps affect veg as well. lower temps, lower respiration & cell division = less growth of foliage...

enjoy your garden!

 

[johnipedestran]

my personal experience having run both ways (in no way a proper test) for a few years now....i would say that plants do a lot better with some dark period. i run 20/4.....

i notice some plants, particularly indicas show some tiredness/wilt, just before the dark period is due to begin.

i think they just need some rest.

peace
jip

 

[FreezerBoy]

When I ran 24/0, I was never surprised by growth when I opened the cab in the morning. Since switching to 18/6, I'm ALWAYS surprised by growth in the morning.

 

[coolx]

FYI - tests have been done (and the results are here somewhere on ICMAG) and greatest biomass is produced by 20/4, 10% more than 18/6 and then I'm not sure if 24/0 or 16/8 was next.

 

[ninsega]

I always thought the 24/0 cycle was for making sure your seeds all pop out of the soil. All depends how you start your grow I suppose. Other than that science would let you believe growth only occurs during the dark cycle, but considering plants do grow under 24/0 that is proven wrong.

 

[Closet Funk]

This is an interesting topic. From what I've read cannabis doesn't need a dark cycle for veg growth only for flower. I usually run my veg under 24/0 but lately it's been 20/4 just to cool the ballast for awhile. I guess it's good for plants to get some darkness because it's in the natural cycle, but I don't think leaving the lights on all the time will have any stress. Otherwise plants would show it.

 

[LJB]

I would love to try this one with Cannabis:

Diurnal changes in net photosynthetic rate in potato in two environments

Joginder Singh Manhas1 and N. P. Sukumaran1

(1) Central Potatc Research Institute, 171 001 Simla, India
Accepted: 5 November 1987

Summary Diurnal changes in net photosynthetic rate were measured in a furrow-irrigated potato crop and in a riverbed crop where the water table was always maintained at 20–28 cm from the soil surface. In the irrigated crop, the photosynthetic rate during mid-afternoon was about half the peak rate observed at noon. This reduction was accompanied by a near tripling of stomatal resistance, a 45% reduction in transpiration, and a 5-fold increase in the difference between leaf and air temperatures. No such changes were observed in the riverbed crop where the photosynthetic rate remained nearly constant at about 0.9 mg m−2 s−1 between 9 a.m. and 4 p.m. Tuber yield in the riverbed crop was about 30% higher than in the irrigated crop.

free full text .pdf at the link

(potato is another C3 plant)

 

[THC_Decapitator]

i get the fastest growth using 20/4 . Ive tried 24 and 18/6 etc

 

[johnnyla]

Could it also be said that there doesn't exist in Nature, conditions equal to hydroponics ?
I'm always amazed at folks growing plants in a bucket of nutrient-rich water, rather than SOIL.
While it may be possible to grow plants this way, I feel something is lost through this unnatural process.

Any thoughts ?

Romans used hydroponics. It's really not new at all. Maybe the chems.

 

[Owl Mirror]

Here are a few things to make you think how conditions can affect the plants growth.

a table of the duration of daylight or darkness for one year.

PHOTOVOLTAIC ROOT STIMULATION

ULTRASONIC PLANT STIMULATION

 

[Greyskull]

my experience has led me to prefer 24/0....

lots of ways to skin the cat but gotta find the way thats best for you.

reading is nice but 'action' is better.

 

[VerdantGreen]

interesting topic - thanks. i tend to veg under 16/8 for economic reasons and also, because my airflow goes from my veg cab into my flower cab, i try to have the C02 produced by my vegging plants in their dark period suppliment the natural C02 flor my flower cab.
i like the idea of trying to keep the arcadian rythms constant and may change things round a little bit.

V.

 

[Normannen]

Just FYI tha strongest plants grow below the 24/0 belt. Here in the north above 70° it's called grassland because plants like trees can't grow properly (EDIT unless they are conifers and still those stop growing when they hit the permafrost) during the summer even in greenhouses...that's why we cultivate our hydroponics in greenhouses in the south and "export" them to the north...
and no i'm sick and tired of the midnight sun it's as spectacular as a sunset in Tahiti...at least in Tahiti you get to sleep after midnight.
Personally....i prefer Northern Lights ;P