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  1. #1
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    Extended photoperiod for vegetable seedlings


    0 Not allowed!
    This year the wife and i are getting serious about growingnvegetables. Well...cannabis does great wjile under 24 hr of supplemental lighting. We currently have got NUMEROUS plants/seedlings including squash, peppers, tomatoes and herbs. I have been researching the affect of extended photoperiods for our vegetables and i had my suspicions of lights affecting different vegetables differently. My first page of research revealed this link

    https://www.actahort.org/books/481/481_54.htm

    Text to follow...
    Abstract:
    In northern regions, the major factor limiting winter greenhouse production is low natural light. However, it has been demonstrated that using supplemental light from high-pressure sodium vapor (HPS) lamps from November to March achieves increased growth, productivity and gaseous exchanges of vegetable crops such as tomato (Dorais, 1992; Dorais et al., 1991; Vézina, 1989; Vézina et al., 1991), cucumber (Turcotte and Gosselin, 1987, 1989), pepper (Demers, 1990; Demers et al., 1991) and lettuce (Gaudreau, 1991; Gaudreau et al., 1994).
    Most research on supplemental lighting has concentrated on the effects of the amount of light on crops; little work has been done on the influence of the photoperiod. In practice, greenhouse vegetable growers generally use photoperiods of 14 to 17 hours. Greenhouse tomato plants (Lycopersicon esculentum Mill.) exposed to photoperiods of 20 and 24 h developed chlorosis on their young leaves (4th to 7th leaf from apex of plant) (Bradley and Janes, 1985; Vézina et al., 1991). Moreover, the productivity of tomato plants subjected to a 17-h period did not increase compared with a 14-h photoperiod (Vézina et al., 1991). Extending the photoperiod to 20 to 24 hours even reduced plant productivity (Vézina et al., 1991). Foliar chlorosis and reduced productivity also occurred among tomato plants exposed to a photoperiod of 17 h where the 7-h nocturnal period had been separated by a 3.5-h light period into two short nights of 3.5 h. (Vézina et al., 1991).

    Extending the photoperiod to 20 h resulted in increased growth and productivity of greenhouse sweet pepper (Capsicum annuum L.) plants (Demers et al., 1991). Compared with a photoperiod of 15 h, continuous lighting (24 h) resulted in earlier flowering and fruiting of pepper plants, giving better early yields, while final productivity was identical for the two photoperiods (Costes and Milhet, 1970). In addition, continuous lighting resulted in smaller average volume of the fruit harvested (Costes and Milhet, 1970). Blistering of the leaves was observed in pepper plants exposed to a photoperiod of 24 h (Costes and Milhet, 1970) and even 20 h (Demers et al., 1991). Slight internerval discoloration of the leaves was noted among pepper plants receiving 24-h light (Costes and Milhet, 1970). Also, foliar chlorosis and loss of leaves was observed in pepper plants grown under uninterrupted light (Nilwik, 1981).

    We found that exposing tomato and pepper plants to long photoperiods (tomato: over 17 h, pepper: over 20 h) resulted in negative effects such as chlorosis or blistering of leaves. In addition, long photoperiods also reduced growth and productivity. Where long photoperiods do not have negative effects on plant growth and productivity, the plants do not appear to benefit or utilize the additional light. Many questions arose from these early measurements: Why leaf chlorosis does appear? Why tomato plants cannot be cultivated using photoperiods exceeding 17 h, while pepper plants tolerate a photoperiod of 24? Which physiological processes are affected by long photoperiods?

    No clue what chlorosis is....next post

  2. #2
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    Chlorosis

    In botany, chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green color of leaves, chlorotic leaves are pale, yellow, or yellow-white. The affected plant has little or no ability to manufacture carbohydrates through photosynthesis and may die unless the cause of its chlorophyll insufficiency is treated, although some chlorotic plants, such as the albino Arabidopsis thaliana mutant ppi2, are viable if supplied with exogenous sucrose.[1]

    Chlorosis is derived from the Greek khloros meaning 'greenish-yellow', 'pale green', 'pale', 'pallid', or 'fresh'.

    In viticulture, the most common symptom of poor nutrition in grapevines is the yellowing of grape leaves caused by chlorosis and the subsequent loss of chlorophyll. This is often seen in vineyard soils that are high in limestone such as the Italian wine region of Barolo in the Piedmont, the Spanish wine region of Rioja and the French wine regions of Champagne and Burgundy. In these soils the grapevine often struggles to pull sufficient levels of iron which is a needed component in the production of chlorophyll.[2]

    So currently i have seedlings of vegetables under 24 hr supplemental lighting. Given the research i have unearthed i will post back to either dispel the myths OR reinforce the facts (Capt. Obvious)

  3. #3
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    0 Not allowed!
    I would like to confirm that peppers show minimal affect by being exposed to 24 hr lighting. They aren't notably larger than ones not exposed to supplemental lighting. On the other hand the tomatoes showed dramatic results ny being exposed to 24 hr lighting. Yet i did not experience the chlorosis the study spoke of. Perhaps if we let the planta get larger than 4" and allowed them to flower (under supplemental lighting)...(are they photoperiod?)...(more research needed)...IF they were allowed to grow larger...perhaps they would have experienced chlorosis. But tomatoes luv supplemental lighting. 1523153182498894459538.jpgmatter of fact the wife got the gardening bug hard this year. She made an elevated bed for peppers1523153295362842748988.jpgtheres the raised bed planters. They will be in my 2018 grow journal1523153391685615356591.jpgthis is the little garden we have going on so far. Some vegetables amd herbs15231534880261401286073.jpgcouple of seeds/plants out as well to see if its okay to put my stuff out. That plant is a male (blue cheez x mango) and will be harvested for pollen. But it and another, is testing the hours. If they don't flower this week i gonna put the real one out. 1523153666784350836744.jpg

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