Daylength and the appearance of first flowers

I wanted to pass on the results of a little experiment that I have just completed as others might be interested in the info.

I wanted to know how many days it took from the time my plants were exposed to 13.5 hrs of daylight before I began to see the first flowers and then, the first buds. I chose the daylength of 13.5, because thats the daylenght I assumed I had at 38 degrees on Aug. 1, which is the date I normally see flowers. Ive seen this in several daylength charts for my lat.

First let me say that all 4 of the plants in my experiment are mostly indica, over 80%. 3 cream caramel from sweetseeds and 1 Sadhu from Mandala.

On July 3, I began setting my plants in the grow shed for a period that resulted in 13.5 hrs of daylength . On that date, the plants were fully in the veg stage. The first visible changes in the plants came 4 days later, when the small shoots in the branches began to thicken and change color to purple. The first real flower appearance was on the 11th, 7 full days after I began the dark treatment. The first real bud appearance occurred during the day of the 14th of july, eleven days after the 13.5 treatments began.( I have some pictures showing these flowers but cant upload, ill continue to try)

My conclusions after this rough experiment were that it took about a week after 13.5 was reached to see the first flowers and 11 days or more before small buds were observed.

Shorty after believing I had leaned something, I made a discovery that threw my 13.5 hr belief into chaos. At my lattitude, 38, first flowers for indica strains are seen by Aug 1 generally. Given that my results would indicate that it takes about a week for flowers to appear after appropriate light levels are seen, logic would suggest that here at this lat, the trigger date for flowering is approximately July 23, or 7 days before 8/1.

Today is the 16th of July, and according to sunrise/sunset as listed in the daily paper, sunrise is 6:29 and sunset is 8:59, which is 14.5 hrs. It appears from following the sunrise/sunset times for a week that I am loosing around 3 minutes of daylength per day, indicating that a week from now, I will be at about 14 hrs and 7 minutes of daylength, which I can only conclude that this is the daylength that at my lattitude, will trigger flowering. 14 hrs and 7 minutes sound like a long daylength to me.

My real problem with this number is that i disagree with the papers assessment of when sunrise/sunset begins. I would add at least another 30 minutes to their length because the level of brightness at 6:15 am is significant, as it is at 9:15pm. This would mean in real terms that my indica plants are really being kicked into flower around july 23rd at about 14.45 minutes of daylength, and that is very puzzling to me. Isnt that extremely high? (yes, i was too during most of this experiment)

Anybody have any thoughts or input regauding these astounding findings and conclusions?

Huh, interesting idea for an experiment. Being a first timer outdoors I've been wondering the same thing for the past month or so. Im a little more North, about 42 degrees. According to one of the stickies about daylight periods, I have about 2 weeks till 14.5 and a month or so till under 14 hours of light. Personally I didn't think they would start flowering at all until 14 hours. I agree with you though about the amount of light at sunrise/set. My plants get direct sun from maybe 7:30am? to about 5:30, but its pretty light when I get up at 6:30 and it stays bright till at least 9. But it lists sunset @ 8:20. I know this isn't very helpful, just my 2 cents. I'll definitely keep track of when flowering/budding starts though.

i'm at 35 degrees and all of my white label northern lights have started to flower... BUT it has been raining for the past week and a half so................

I am just north of the 36 line and some males are already growing balls? I also Have one girl that has been flowering for a few weeks now? I guess it is what you call an auto flower. Should I be worried about a plant like this going hermie on me? I am wondering if all the smoke has anything with flowering early.

Yeah man dont forget about twilight. Before sunrise and after sundown there is still light hitting your plants.

Hi everyone.
I guess the biggest suprise for me was the amount of daylight at the time the plants must be triggering to flower which appears to be about 14.5 around July 23. I always new that most indica strains would trigger by 14, but not 14.5. I had never looked in the paper to see their designations of sunrise/sunset.

Rob547, check the daylength at when you first see flowers and let us know.

BigWillieDee, Ive grown NL several times from different banks and every time it has started to flower before the end of July at 38. I don't know your experience but I consider NL one of the earliest hybrids available. I don't think thats widely known. Look in the paper and tell us what it says your daylength currently is and if its really light and dark at those times. Here, at 6:29, you don't need headlights at all.

BF, generally males flower before females so thats not unusual. The females should start in the next couple of weeks. Its certainly no indication of hermaphroditism, so don't worry about that. The one thats been flowering a few weeks probably is an auto. I don't know of anystrain that would be in full flower at the first of july that isn't.

And a lot of it chubbynugs. I was being very generous when I only added 15 minutes to the papers sunrise/sunset time, but in reality, its daylight here in my mind by 6:05, not 6:29.

im at 39n and i havent bee to my plot in 10 days. About to go out no and check it out. Ill be back with updates

silverback said:

Hi everyone.
I guess the biggest suprise for me was the amount of daylight at the time the plants must be triggering to flower which appears to be about 14.5 around July 23. I always new that most indica strains would trigger by 14, but not 14.5. I had never looked in the paper to see their designations of sunrise/sunset.

Rob547, check the daylength at when you first see flowers and let us know.

BigWillieDee, Ive grown NL several times from different banks and every time it has started to flower before the end of July at 38. I don't know your experience but I consider NL one of the earliest hybrids available. I don't think thats widely known. Look in the paper and tell us what it says your daylength currently is and if its really light and dark at those times. Here, at 6:29, you don't need headlights at all.

BF, generally males flower before females so thats not unusual. The females should start in the next couple of weeks. Its certainly no indication of hermaphroditism, so don't worry about that. The one thats been flowering a few weeks probably is an auto. I don't know of anystrain that would be in full flower at the first of july that isn't.

And a lot of it chubbynugs. I was being very generous when I only added 15 minutes to the papers sunrise/sunset time, but in reality, its daylight here in my mind by 6:05, not 6:29.

Click to expand...

The auto fower is the only one that confuses me. Yeah I know the males always show first, LOL. It just seems that some are way early this year. I did have one female herm on me last year. I am going to keep a close eye on that autoflowering girl.

well the paper has it as 5:27 & 7:44 however like everyone else it is usually light enough to see from maybe 5 till 9-9:30 so.....i think the early tendency of the strain with all the rain just pushed me forward a little...

i checked another area today with some freebie seeds thai haze x skunk and nothing has shown yet.

Hey NickMode, we'll be waitin

You know BF, it seems like i hardly ever grow a strain, any strain, that I dont find a seed or 2 during the winter when its being smoked, and you can tell it was a male flower on the plant and not some drifing pollen because all the seeds will be in one or 2 buds and not others.Its impossible in my view to find a male flower on a big plant in the field. In fact, I find fewer seeds in the femminized strains I grow than i do in the standard strains. Female cannabis plants often produce a male flower or 2 and I dont think theres much you can do about it.
That's different of course than having one with manberries all over it.

hi...

That period before sunrise and after sunset when there is still light is called: civil twilight- The period between astronomical sunrise or sunset and the time when the sun's unrefracted center is at elevation h0 = -6°. So in my view you need to add those minutes/hours from civil twilight to sunrise/sunset and you have complete daylenght, when light is still hiting plants. hope I wrote clearly. hehe.

In my case as of 16.7. at 46N

sunrise: 05:26.47 AM sunset: 08:48.42 PM lenght: 15:21.55

end of civil twilight:

sunrise: 04:49.55 AM sunset: 09:25.27 PM lenght: 16:35.32

there is 1h+ to add to that sunrise/sunset chart at this time of the year.

as of 15.7: 2 marocs are flowering, 1 quick mist male was trashed it had many balls.
last year marocs started to flower sometime on 22.7...


all the best.

BWD, Ill bet that indica's respond under more light than sativa laden strains. That thai/haze skunk is mostly sativa and that may be why it hasnt responded yet.

Dang ss, thats a long day for cannabis to flower. In fact you have to consider it was really a some time ago that the plant was actually triggered to flower.
You know, I want to add an hour to the sunrise/sunset times their reporting in the paper. Its light outside. I guess one would have to have a light meter to really know for sure. One would have to measure the light emitted from a full moon because thats not enough light to impact the plant, and at times with a full moon you don't even need a light to be outside.

math and genetic variation makes for a difficult equation

Supersonic: You are correct, that you have to count twilight in the equation ,not just sunrise and sun set to get the daylength. Another determining factor in the flower formation is the speed at which the days are getting shorter. IE: On June 21 the daylength is at is longest. On June 22 the daylength my only be a few seconds shorter. On June 23 a few more seconds shorter. As you head for the winter solstice the day length shortens faster and faster untill October where you are loosing over three minutes of daylength per 24 hour period. Some plants arent triggered to flower so much by the length of daylight, but by the decreasing length of daylight from one day to the next. Make sense?

Jungle Jim: yes it makes sense. at 16.8.2008 at 46N will be: sunrise/sunset: 14:05.54.......
civil twilight: 15:10.56.... that seems to be still long daylenght for flowering but in my experience 80% if not all plants will flower by then. on the other hand, day and civil twilight shortens from 16.7 to 26.7 for 20 minutes. thats 2 minutes a day and that's pretty quick...so yes it must play role in trigering plants to flower...

ss

Thats very interesting Jungle Jim. In fact, it may explain a condition that I know exist in cannabis whereas certain shading situations trigger flowering faster. Ive had plants of the same strain, sometimes only 20' or so apart where one of the plants goes into the shade before the other and the plant starts and finishes as much as a week more than its sister. The effect is increased as the end of summer approaches and the sun starts lowering in the sky, consistently lowering the daylight recieved by the shaded plant. I know it happens. Your statement that the rate at which daylength decreases may provide an explanation for that effect.

yo silverback, told you I'd get back to you about my first signs of flower. Went to see them on the 12th, they had some more pistils, but I wasn't really counting it as starting to flower. Today I went out again and they had actual (very) beginnings of buds, pistils coming out of the top of the budsites, so yea....I'll call it August 13-15. Back around the 12th daylight hit exactly 14 hours, today its 13:52.

pretty interesting stuff silverback ,,, the sun seems to have different habits in the northern hemisphere to where i live on the southern tropical zone ,,
our sun sets and rises pretty fast ,, not much lag time like it seems u guys experience , something to do with the bulge in the middle and southern hemisphere im told ...
how long do u reckin its taking your plants to react to the waning hours ??
im guessing your daylight hours are dropping pretty fast by the time flowering begins ??