Lights on 24 hours versus 18/6 for cloning/veg, whats the final word....

Professor Manali

Professor Manali

Member
I was posting in another thread because someone started talking about respiration being independent of oxygen in the dark, quoting rollup himself as saying that the plants need this dark period.

I dont know about any hard facts about this, but I had a few thoughts, and wondered what the definitive answer is to this debate.

The way I see it, but I'm just putting this out there, is that during the light period, plants are photosynthesising (ie making sugar and producing oxygen, using up CO2) and theyre respiring (breaking down sugar to release energy for growth and maintenance). Respiration happens at full tilt during the lights on time, cos theres a constant maximum supply (ideally) of sugar available from photosynthesis. In fact they store it as starch, or send it down to the roots and stem for growth. If the lights go off, then theres still plenty of carbohydrate about, but sugar levels would start to drop soon enough, and starch would start to be broken down to provide sugar. Seems to me that respiration slows down during a lights off time, but its not independent of oxygen. Its the dropping O2 levels (its not being produced in the leaves in the dark) that cause the slow down in respiration, as much as the dropping sugar levels is responsible.

IMO, and I aint no botanist or anything, the only reason I can see why a 18/6 cycle is better than a always on regime, is that you dont lose that much growth to make it worth spending the electricity on it. The plants continue to tick over nicely in the dark.

I dont really know any of this for sure, btw, I just figure....:smile:. And I felt like a good rant, you know what I mean...
 
Phillip J Fry

Phillip J Fry

Active Member
idk tbh , but the thought is all of the plants energy can be used in the dark period to do its thing with stored nutes, but when the lights then they use energy gathering nutes. Thus leading me to believe in the dark the plant would be more effective at using nutes, as long as enough are stored to last the given dark time.

note: this is just what i gather, not sure if its right....
 
BeaverHuntr

BeaverHuntr

Well-Known Member
Im keeping a white russian mother under my T5 at 24 hrs lights on and its still growing and drinking about 3 gallons of water every week.
 
U

uhavealighter?

Active Member
yeah not really much of a difference. Id go 18/6 and cut on your electricity bill. You notice how they grow faster the first few weeks the plant are on 12/12?
 
cadeneli

cadeneli

Active Member
I go 24/0 when growing from seed and 18/6 when growing clones. 18/6 allows for a better root system.
 
legallyflying

legallyflying

Well-Known Member
There is no definitive answer as people believe whatever they think is true. As a professional botanist and fairly proficient mj grower, show me any C3 or c4 that grows naturally in a 24 hour light cycle and I'll switch from 18/6. I'm thinking about going 16/8 or less for the exact reasons given by the original poster.

The link above leaves out an important part of the dark cycle and that is the UTILIZATION of stored sugars and amino acids.

Been doing my homework on this lately and came across this ...

"Plants use periods of darkness, too. During dark periods, plants continue to take in oxygen, and give off carbon dioxide in a process called respiration. During this time, the plant uses some of the energy that was stored as sugars during photosynthesis, producing proteins, hormones, and other complex products. Therefore, lighting mature plants more than seventeen and a half hours per day will not increase production significantly, since photosynthesis will slow down after a certain number of hours. In fact, too many daylight hours can actually be counterproductive, delaying or preventing flowering in some crops."
 
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