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how much light for a seedling?

Discussion in 'Newbie Central' started by 420keepitgreen420, Sep 13, 2011.


    420keepitgreen420 Active Member

    as you can see the title how much light for starting a seed? 12/12 24/7 what is it please help me out here guys

    Nusky New Member

    18/6 or 20/4

    cranker Legal Moderator, Esq.

    0 light for starting a seed

    mazand1982 Active Member

    18 on 6 off is the best in my opinion because it saves electricity and you notice that the plants grow a little better when they have a period of dark from what i seen and experience.

    Jloi Well-Known Member

    I germ my seeds, once they have a tap root then I plant them. With that said I keep the lights on 18/6 with total blue spectrum. You can do 0 lighting until something pop's up but it will take longer. Remember these seeds grow wild in lighting.

    skunky713 Member

    Im on my first grow ever i just put mine in the light for 24 hrs straight and 6 off now im going 18 and 6

    mazand1982 Active Member

    thats good bro, you should be just fine. click on my grow , i grew from seed and they are 2 weeks into flower and look beautiful, ask away if u need help, this is not my first grow but i remember mine and iud be happy to help if needed.

    Jloi Well-Known Member

    Be careful with your lighting bud, changing your lighting adds added stress to the plant, added stress has more of a chance you will get a male or hermi plant.
    Good luck on your grow! If you ever got any problems just ask, and don't react right away if you have problems. People tend to start chasing problems then!

    skunky713 Member

    preciate man will do... im so new at this i been watching video after video on youtube and reading just about every grow guide online

    skunky713 Member

    ok thanks for the info.. i was thinking if i changed the light like that it would add some stress on the plants

    Jloi Well-Known Member

    If you changed it from 24 just to get a plant growing to 18/6 you'll be fine. Just dont bounce around with your lighting that when you'll run into problems.

    skunky713 Member

    ya it popped its head out this morning i then i turned off the lights for 6 hrs came back it was 2-3 inches long i was amazed im on day 2

    PlanC Active Member

    Hey guys. I am on my first grow as well. I have a 400W mh bulb in a silver star enclosed reflector. I just germinated some seeds my buddy gave me and put them in in some peat moss cubes(about 3mm deep). I turned the light on right away and have it set on a 18-6 schedule. I covered the cubes with a clear plastic dome. The average temp during the first 18 was 80F with a 50%humidity. My question is will they be ok under such a strong light. I really don;t want to go out and spend more money on cfl's. Thanks

    frmrboi Well-Known Member

    24/0 is best. -Ed Rosenthal
    This is a direct quote from Ed Rosenthal whom most of you know is a marijuana growing guru:
    marijuana plants photosynthesize as long as they receive light as well as water, air, nutrients and suitable temperature. Photosynthesis is the process in which plants use the energy from light (primarily in the blue and red spectrum's) to combine carbon dioxide (CO2) from the air and water (H2O) to make sugar while releasing oxygen to the air.
    Plants use sugars continuously to fuel metabolic processes (living) as well as for tissue building. The plant combines nitrogen (N) with the sugar to make amino acids, the building blocks of proteins. They are the substance of plant tissue. When the light is off, the plant's metabolic processes, respiration and growth, continue.
    The plant can photosynthesize continuously so it produces the most energy and growth when the light is on, continuously. Continuous light does not stress the plant, which reacts somewhat mechanistically to it.
    Plants under an 18-6 light-dark regimen are producing sugar only three quarters of the time. They are thus growing at only 75% of their potential. Leaving the light on continuously will result in bigger plants, faster, which leads to higher yields."
    "The following information is straight from Greg Green's "The Cannabis Grow Bible"
    Cannabis is a light demanding plant. Professional growers keep the light on their plants using the 24/0 photoperiod for this reason. Plants that grow under 24/0 flourish and do not need a quantity of darkness in order to rest and perform photosynthesis properly. Plants that are grown in optimal conditions under 24/0 light regime grow vigorusly and the benefits of a 24/0 photoperiod can be seen actively in the results. More nodes are formed, more branches are created, leaf numbers increase, the plant is growing at its finest.
    Some growers opt to use 18/6 as their photoperiod. This is 18 hours of light, six hours of darkness light regime. Under these conditions the plant will grow quite naturally but not as vigorously as the 24/0 photoperiod.
    The 18/6 photoperiod expels 3/4 the amount of light that a 24/0 photoperiod does. Although this does not mean that a plant produces 1/4 less leaves,branches and nodes under the 18/6 photoperiod, it certainly does show the correlation between light and cannabis growth. As we have said already, cannabis is a light demanding plant. There are no problems associated with 24/0 and although some have attributed cannabis sexual dysfunction (the hermaphrodite conditon) to 18/6 photoperiod these problems are actually the result of heat stress.
    A 24/0 photoperiod requires that your grow room temperature be kept well monitored. The 18/6 option is cheaper to run. You use a quarter less electricity and this will have an impact on your electricity bill. Also the 18/6 photoperiod will generally extend the bulb's lifespan. During the 6 hours of darkness the grow room is allowed to cool down for this period but a well maintained good grow room setup should not require a cooling down period.
    24/0 and 18/6 both share the same problem though. Once you start the photoperiod you should keep that way especially when the plants near maturity (the preflowering stage). An irregular photoperiod can cause more males than females to develop. It can also cause sexual dysfunction to appear. Whether you choose 24/0 or 18/6 as your vegetative photoperiod try to keep that photoperiod unitl your plants are mature enough to express their sex."
    24/0 is superior insofar as plant growth
    Most green plants are classified as either C3 or C4 which represents how carbon(C) is used during photosynthesis.
    C4 plants temporarily store carbon dioxide(CO2) over the dark period to use for photosynthesis during the day. C4 plants slow down photosynthesis once the stored CO2 is used up and they need to gather it from the air. Which is why trees slow down photosynthesis in the afternoon even though the sun is still bright. This does NOT apply to cannabis.
    C3 plants(cannabis/veggies) gather CO2 only during the light period when they are photosynthesizing. During the dark period these plants only use oxygen for their metabolic life processes. They don't uptake CO2, nor do they use it. As soon and as long as the light is on, C3 plants gather and use CO2 for photosynthesis.
    C3 plants also have the ability to use higher concentrations of CO2 than what is found in the air. If the light is bright enough and the plants have sufficient nutes, their growth rate will accelerate from it(2000ppm vs. 400ppm of CO2), which increases yield. They can do this continuously, wihtout a dark period throughout the vegetative stage.
    The dark reaction is a process of photosynthesis that takes place in both darkness and light. It uses ATP and NADPH molecules that hold energy absorbed from light to break apart CO2 into it's base components. Because it's called a dark reaction and can occur in the dark, some people(Jorge) have said darkness is needed for this to occur. This Is Not So.
    Again people get anthropomorphic with their plant needs. People need rest, so plants must too. This is false as well. Light means growth. Scientifically. Although 18/6 will shock your plants less when you switch to 12/12, it's a personal choice whether you would rather sacrifice a little growth for a quicker adjustment or less photo confusion. If you want to save money or energy that's a personal choice too. Do what you need to do to make your growing scenario work.

    Wetdog Well-Known Member

    IDK, I just put mine in old used mix, set them out on the deck in full sun and let nature take its course.

    Why complicate something as simple as planting a seed?


    mrmadcow Well-Known Member

    while your plants may not need a rest period, if you are using an old style mag. ballast HPS or MH, your ballast will need a rest. most manufacturers recomend a couple hrs a day. it will make your ballast & bulbs live longer.
    I like a 20/4 hr day personally, tried 24 hrs on & didn't see any advantage.

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