"Photoperiodic"- Please enlighten me.

[dcarch]

This winter, I am trying to grow a few varieties of tomatoes indoors. I have been having problems of leaves turning brown, and I posted some pictures in the “Common Garden Diseases and Pests” Forum “Lime Brown Salad!” trying to find out what’s going on.

http://www.tomatoville.com/viewtopic.php?t=3401

I am shifting the topic in this forum because in trying to identify the causes I have come across a terminology “Photoperiodic” which I don’t think has been discussed much before and I think possibly may have some relevance to my situation.

I have been supplementing the windowsill sunlight with metal halide light (250w). The combination of sunlight and MH light comes to about 16 to 18 hours of light each day.

Anyone can give me some input on:

1. How many hours of illumination to give before you do damage to tomato plants?
2. Is there any data on how many hours of darkness to encourage flowering and fruiting?

Thanks

dcarch

[ZBQ]

dcarch,

Type this into Google and you will have a wealth of info.

photoperiodism in tomatoes

That is the proper term for it and applys to all plants and animals has a substantial effect on humans as well.

Here is an article about tomatoes.

http://www.ri.net/schools/Narraganse...background.htm


Hope this helps.

[username5]

Originally Posted by dcarch

I am shifting the topic in this forum because in trying to identify the causes I have come across a terminology “Photoperiodic” which I don’t think has been discussed much before and I think possibly may have some relevance to my situation.

I believe the link given by ZBQ does a nice job of covering the relevant terms.

I have been supplementing the windowsill sunlight with metal halide light (250w). The combination of sunlight and MH light comes to about 16 to 18 hours of light each day.

This should be adequate for good growth. I use a 400 watt HPS + sunlight from a south facing patio door.

Anyone can give me some input on:

1. How many hours of illumination to give before you do damage to tomato plants?
2. Is there any data on how many hours of darkness to encourage flowering and fruiting?

You could give the tomatos 24 hours of light without damage. Tomatos are not influenced by duration of light for anything. Their vegetative, flowering, fruiting stages all occur for reasons other than duration of day/night.

While there are some who could make a good argument that 24x7 light is harmful to plants in the long term, it isn't harmful in the short term. Any plant grown in the Alaskan summers is proof of this. Some indoor growers, in an attempt to get fruit as quickly as possible will leave lights on 24x7. Whether or not this actually will result in faster development seems to be a matter of some debate, but in my (limited) experience it does appear to.

In short, whatever the cause of browning leaves is, it isn't the duration of light your plants are getting.

[amideutch]

Dcarch, There are a few books at amazon that might interest you if you are interested in growing under lights.
Both books are by George F. Van Patten.
1. Gardening Indoors (New Revised) ISBN: 1878823116
I have this book. Chapters on lighting, growing medium and hydroponics just to mention a few areas it covers.
2. Gardening Indoors with H.I.D. Lights.
ISBN: 1878823213
Hope this helps. Ami

[dcarch]

There has been ton of discussions on every topic, I just find it very interesting why there is not much discussion on the total impact of light other then the fact that you need about 6 to 8 hours sun light per day.

Here is something I found which led me to wonder if too much light mught do damage:

Presenter: D'Silva, Lorraine I Contact Presenter
Authors D'Silva, Lorraine I (A) Micallef, Malgre C (A) Coneva, Viktoriya (A) Micallef, Barry J (A)
Affiliations: (A): University of Guelph

Photoperiodic injury of vegetative tissues can occur under either extended photoperiods or non-24 h light/ dark cycles. The physiological basis for this injury is unknown, although the involvement of circadian rhythms has been proposed. Processes involved in N metabolism are known to show circadian patterns, and two toxic compounds (i.e. nitrate and ammonium) are produced during nitrate reduction. We tested two hypotheses: (1) differences in susceptibility to photoperiodic injury will be associated with differences in circadian rhythm patterns; and (2) nitrate or ammonium toxicity is associated with photoperiodic injury. Tomato is particularly susceptible to this injury, and tomato cultivars that demonstrate variation in susceptibility to photoperiodic injury were identified. The cultivar Micro-Tom showed no injury under all conditions tested, whereas the cultivar BasketVee displayed the most severe injury. Patterns of cotyledon movement and stem elongation were tested under either a 12 or 24 h photoperiod, and a correlation was found between susceptibility to photoperiodic injury and the ability to maintain normal circadian rhythms under a 24 h photoperiod. Leaf nitrite levels elevated significantly prior to the development of photoperiodic injury in susceptible cultivars but not in Micro-Tom, although nitrate and ammonium levels either remained the same or decreased. Photoperiodic injury symptoms could be induced using the nitrate-analogue chlorate, which is converted to the nitrite-analogue chlorite. We propose that the physiological basis for photoperiodic injury in plants is nitrite toxicity resulting from an altered coordination between nitrate and nitrite reduction activities under photoperiodic cycles favoring the injury.

dcarch

[username5]

dcarch,

The quote you gave resulted in a mild chuckle. Sometimes there is research that makes conclusions, but the authors indicate they really don't know.

I am hesitant to use the term here, in polite company, but among my ruffian friends I don't hesitate to use the term 'mental masturbation' to describe much of this 'research'.

Everytime I encounter a person who thinks 24x7 light is bad for plants I point them to Alaska.

Bottom line is your 18 hour light cycle is just fine and isn't causing any problems. For annuals you could switch to 24 hours of light without any problems other than a little higher electric bill

One can research the issue to death and find all sorts of academic reasons why different light/dark intervals are good/bad, but unless the plant actually requires light/darkness duration to switch into the next phase of development, it just doesn't make a hill of beans worth of difference in the real world. Longer light=faster growth, shorter light=slower growth.

If this wasn't the case nobody would be able to grow much of anything in Alaska where they are dependant upon their nearly unending summer time days to grow crops quickly before the snow flies again.

[kimera]

For indeterminate varieties, I suspect that there's a lot of latitude on the hours of light per day. I've got about 30 tomato plants of several varieties in a hyrdroponic unit, and I'm growing them under a 1,000 watt metal halide light. It turns on at 7:00 in the morning and turns off at 6:00 in the evening. After about six weeks from seed, I have plants that are in the 12" to 18" range, and several are beginning to flower.

[dcarch]

Originally Posted by username5

-----------------If this wasn't the case nobody would be able to grow much of anything in Alaska where they are dependant upon their nearly unending summer time days to grow crops quickly before the snow flies again.

That's certainly very convincing argument. I have no choice but to accept it. Somehow, I just feel that insomnia is not good for tomatoes.

Thanks for shedding light on this topic. :wink:

dcarch

[username5]

Originally Posted by dcarch

That's certainly very convincing argument. I have no choice but to accept it. Somehow, I just feel that insomnia is not good for tomatoes.

Thanks for shedding light on this topic. :wink:

dcarch

Thank you for your humor, but you do touch on what all the controversy is about.

See, plants have to do many things in order to survive. To put things into human terms they must breathe in and breathe out. Commonly it is believed that plants 'breathe in' during the day and 'breathe out' during the night.

To go any further requires me to speak well beyond what I actually understand.

To make things simple so I can avoid technical inaccuracies, there might well be problems with forcing *perennial* plants to endure long durations of 24x7 light. I honestly don't know.

For annual plants or for plants treated as annuals it doesn't seem to matter health wise if they get 24x7 light.

In the real world I don't think anyone gives perennials 24x7 light. The main group of folks giving plants 24x7 light are marijuana growers and their plants are short lived (although many clone female plants for many years).

Now, growing pot is illegal in most jurisdictions and I am certainly not looking to turn tomatoville into overgrow.com, but those 'potheads' at the latter mentioned site are working with a plant that is strongly photo period sensitive and they have done wonders in terms of indoor, artificial light cultivation using 24x7 light followed by 12 hours of light and then 12 hours of total darkness.

In fact marijuana is successfully grown outdoors even in Alaska thanks to the experiments of folks like those at overgrow.com who have worked to perfect growing a drug plant, but in reality have unwittingly stumbled upon more information that most can take in in a lifetime concerning plant response to varying durations of light/darkness.

If only there were growers as dedicated to growing tomatos as weed!

Of course none of this would have been possible without draconian drug laws spurring investigation and innovation

If you want to take tomato growing to the next level, petition your government to outlaw tomatos