[floral]

Chopping in darkness is such a PITA I was hoping to learn that the practice was based on superstitious nonsense.

Asked a botanist friend and unfortunately it's true. Posted the full article (with PDF attached) on circadian rhythms and starch transport in the Botany and Advanced Growing Science forum.

One important paragraph says

An important hallmark of the circadian clock is its free-running 24-h rhythm. Free running refers to the fact that, once entrained by light signals, the circadian clock maintains a 24-h rhythm in continuous light or continuous darkness, anticipating dusk and dawn according to previously encountered conditions. In fact, the property of being a 24-h timer has revealed the involvement of the circadian clock in the control of starch degradation. When plants are grown in light–dark cycles shorter or longer than 24 h, abnormal starch degradation patterns are observed during the night. In 28-h light–dark cycles (14 h of light, 14 h of darkness), starch is degraded extremely fast, so reserves are exhausted before dawn—specifically, at 10 h into the night rather than at the actual dawn after 14 h of night (Fig. 1b). Conversely, in 20-h light–dark cycles (10 h of light, 10 h of darkness), starch is degraded too slowly, resulting in the presence of substantial reserves at dawn. If the night is extended beyond dawn, starch is eventually depleted after approximately 14 h of darkness (Fig. 1c).

free-running circadian rhythm = the plants have perfect internal 24h clocks regardless of the light cycle you impose on them

"according to previously encountered conditions" = the plant remembers when dawn and dusk were and times transport so that leaves are completely empty exactly at dawn, ready for the sun to help them cook up some more during the daytime

So it's not just about cutting in darkness, but cutting after a long night that extends just past when the plant thinks dawn is happening.

[floral]

What would be great to know is how long it takes plants to get accustomed to their dawn/dusk routine. They seem to respond very quickly to the flip, so is it just one day?

[mysterygrower]

Good post. Just wish I'd read it back in '92 instead of finding all that stuff out on my own through trial and error. (lots of error)
Many years ago, I Googled round trying to find the optimal time to harvest, nobody had a definite answer, just theories.
I'll probably get shouted down for this but I don't care, I've been doing it for years and never had a bad result; If you need to store weed long term, put it in the freezer.It will come out in the same condition it went in and no, the trichomes won't break off like someone suggested in a chat once. Laying off the ferts during the last two weeks with outdoors definitely helps with taste and burnability. I remember my first couple of grows tasted like crap and was a bugger to keep lit.
Boomshanka.

[Mia]

Solid advice.
Good reminder.

[floral]

Originally Posted by floral

What would be great to know is how long it takes plants to get accustomed to their dawn/dusk routine. They seem to respond very quickly to the flip, so is it just one day?

Rereading the article, full text of which is posted in the Advanced Growing Science forum, it says "immediately".

Remarkably, the rate of starch degradation in Arabidopsis plants can adjust immediately in response to an unexpected early or late onset of night. If plants grown in 12 h of light/12 h of darkness are subjected to darkness after only 8 h of light, the rate of starch degradation is much slower than on previous nights, but remains constant throughout the 16-h night. These observations imply that plants at dusk integrate information about the amount of starch present in leaves and the anticipated length of the night to set the rate of starch degradation. Recent investigations have revealed that the timing of starch degradation in Arabidopsis plants is linked to the circadian clock.

Had read the article a few times but had missed that detail until I went looking for it.

Curious if it would be helpful to give the plants one or two shortened nights before one last long night, to get them used to using up leaf starch at a faster pace. Then on the last night, they keep shipping their sugars away to the roots at a brisk pace and then abruptly run out.

[Oregonism]

Great read by the way, I have two thoughts on this.

1. What about autoflowering or ruderalis species. Their whole genetic make-up is generally a lack of reliance on a circadian rhythm as a trigger for flowering and hence maturation, I am interested to see if there has been an alternate theory of circadian rhythms in autoflower strains.

2. How about indica's grown around the equator? I have heard of growers mentioning that indica's act very similar to autoflowers generally around the equator. What does this say about a compromised circadian rhythm, thru what mechanism is the plant able to adjust?

[floral]

Good questions. Hope someone with the means to do so will research and share the results.

In the meantime I suppose those of us who own brix meters could do some sampling at different times of day, too.

[ThaMagnificent]

Excellent writeup!

[Rotti By Nature]

Thanks for all the great info!!!!!!

[Gruetoo]

Yet another great thread. Never considered the whole starch thing. Will keep this in mind upon the next harvest. But the most important thing I learned..... Have your shit straight or the bugger boo's will come and hammer ya! And give you the proper info.

Gruetoo