How many hours of indoor light per day??

[PaulF]

Learned (or at least heard ) something new. Tomatoes and peppers are day length neutral and do not need a dark period? I always thought all plants required light/dark for respiration. And rest from active growing. Where did I get this? Maybe because that is the natural set-up of the world....day shift and night shift. Am I humanizing tomato plants? Where can I look for this information to learn more?

[ChrisK]

No, many plants do not require a dark period. Respiration happens all the time. Tomatoes can be damaged by continual illumination. Day length neutrality has to do with flowering not whether they will tolerate continual light.

In fact, I think there was a paper published and posted here about a mutant of tomato that can withstand continual illumination.

Originally Posted by PaulF

Learned (or at least heard ) something new. Tomatoes and peppers are day length neutral and do not need a dark period? I always thought all plants required light/dark for respiration. And rest from active growing. Where did I get this? Maybe because that is the natural set-up of the world....day shift and night shift. Am I humanizing tomato plants? Where can I look for this information to learn more?

[ChrisK]

See for instance: Planta January 2015, Volume 241, Issue 1, pp 285-290

Abstract

Continuous light induces a potentially lethal injury in domesticated tomato (Solanum lycopersicum) plants. Recently, continuous-light tolerance was reported in several wild tomato species, yet the molecular mechanisms underpinning tolerance/sensitivity are still elusive. Here, we investigated from which part of the plant continuous-light tolerance originates and whether this trait acts systemically within the plant. By exposing grafted plants bearing both tolerant and sensitive shoots, the trait was functionally located in the shoot rather than the roots. Additionally, an increase in continuous-light tolerance was observed in sensitive plants when a continuous-light-tolerant shoot was grafted on it. Cultivation of greenhouse tomatoes under continuous light promises high yield increases. Our results show that to pursuit this, the trait should be bred into scion rather than rootstock lines. In addition, identifying the nature of the signal/molecule(s) and/or the mechanism of graft-induced, continuous-light tolerance can potentially result in a better understanding of important physiological processes like long-distance signaling.

[carolyn137]

Much less scientific than what Chris just posted but it was always my understanding that with artificial or natural light that photosynthesis made the energy compounds, such as ATP and GTP, etc, that were needed for putting together the larger molecules that were needed for growth and all other aspects of tomato growth and flowering, fruit set, etc, and the dark period was required for all that to happen.

Carolyn

[ChrisK]

The Calvin Benson Cycle reactions are sometimes called light independent but it is really a misnomer.

See: http://ag.arizona.edu/pubs/garden/mg...hysiology.html

A dark period is not required for tomatoes to flower, hence they are considered a "day neutral" plant.

[Worth1]

My stupid brain says that plants and wildlife evolved on this planet with an earth that rotated around the sun.
And a moon that rotated around the earth.
By doing this we naturally have daylight, darkness and tides.
Since the earth is tilted and it doesn't rotate around the sun in a prefect circle we have seasons.
Plus the earth wobbles and we have solar flares creating more complex changes in our environment.
Then there is the dreaded asteroid or comet that comes around from time to time resetting everything and we start all over again.
I cant imagine anything on this earth of ours being the way it is without the earth and our solar system being the way it is.
Consensus, plants need a rest and we need a rest.
Our body produces melatonin as the sun goes down thusly making us sleepy.

Worth

[Tapout]

I personally do a 16 on 8 off schedule for my tomatoes. Why? because I read it somewhere. I never dug into the scientific reasoning.

[Cole_Robbie]

It's funny, when I try to look it up, every other web page says something different.

The intensity of the light involved may play a factor as well. When we are starting seeds under fluorescent lights, they are getting a tiny fraction of the light that would be hitting them in the summer sun.

Here is a research paper from 2005 which found that using fewer lights on a 24-hour cycle was more efficient than using more lights on an 18-hour cycle:
http://hortsci.ashspublications.org/...2/374.full.pdf

That is obviously not the same thing as proof that tomatoes never need a dark period, just an example that seedlings can grow well in 24-hour light.

If I had to guess, if there was a need for a plant to have a dark period, then that need would probably be closely related to the intensity of the light involved.

[ChrisK]

Here's the paper I was remembering (unfortunately behind a pay wall)

A single locus confers tolerance to continuous light and allows substantial yield increase in tomato Nature Comm. 5 (2014) http://doi:10.1038/ncomms5549

An important constraint for plant biomass production is the natural day length. Artificial light allows for longer photoperiods, but tomato plants develop a detrimental leaf injury when grown under continuous light—a still poorly understood phenomenon discovered in the 1920s. Here, we report a dominant locus on chromosome 7 of wild tomato species that confers continuous light tolerance. Genetic evidence, RNAseq data, silencing experiments and sequence analysis all point to the type III light harvesting ?chlorophyll a/b binding protein 13 (?CAB-13) gene as a major factor responsible for the tolerance. In Arabidopsis thaliana, this protein is thought to have a regulatory role balancing light harvesting by photosystems I and II. Introgressing the tolerance into modern tomato hybrid lines, results in up to 20% yield increase, showing that limitations for crop productivity, caused by the adaptation of plants to the terrestrial 24-h day/night cycle, can be overcome.

[Worth1]

Well if I could keep the plants from freezing I would give it a try where I work.
If you guys remember AKMark posted some evidence of plant damage to his tomatoes in Wasilla Alaska.
The pictures showed clearly the sun side of the plants had leaf damage and the shade side didn't.
Up there the sun doesn't go over the top as it does down here in Texas.
Where I work it goes around the horizon at an angle sort of like a halo.
Higher in the south and lower in the north.
Very disturbing in the summer for me as I dont see the sun set for two weeks.

Worth

[PaulF]

Please correct this statement: It sounds to me like the light neutral or continuous light is for tomatoes in the reproduction stage rather than the seedling growth stage and my interpretation of the question was lighted hours during the seedling stage. Did I miss something? Anyway, I can regulate the light in my basement on the seedlings but as soon as the plants are in the ground in the garden I have no control.

[gregory]

This is my 1st time to grow tomatoes from seeds and I have the same set up t-8 with 6500 tubes
My plants are doing well on 16 hours a day. I Just completed my 4th week and they are averaging
4 1/2 to 6 inches plus.

One of my 80 types of peppers, Doe Hill, is flowering under my 24 hour fluorescent lights.

[AlittleSalt]

Originally Posted by LDiane

One of my 80 types of peppers, Doe Hill, is flowering under my 24 hour fluorescent lights.

Wow, 80 types of peppers. Just out of curiosity, how many of each variety are you growing? I'm growing 25+ varieties with 3-7 of each variety in solo cups.

My reasoning for growing so many - "Why Not?"

[Stvrob]

Originally Posted by FarmerShawn

I haven't yet started tomatoes or peppers this year - I have to wait a couple more months. But I do have onions and leeks started. I am running my lights 12 on and 12 off. Would what you say above about tomatoes and peppers also apply to onion and leek starts? The only other thing I have growing under lights right now is microgreens, mostly mixes. They seem to be doing just fine on the 12-hour schedule, but I never tried making it longer for them. I wonder if an experiment is in my near future...

I would be careful with your onions, if you go above a certain number of hours daylight, they will take that as their signal to begin bulbing. I assume your intention is to grow a big strong plant and have it in the ground before bulbing is initialized. Different onion types have different daylength periods before they begin bulbing.

Also, its actually the length of the dark period that triggers the bulbing, though everyone speaks of daylength. Theoretically, you could have say 20 hours of lights on, and 12 hours of light off (complete darkness) and still not initialize bulbing. That would be an interesting experiement to see if you could raise transplants quicker.