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kandm_gw

What are the Consequences of Leaving Lights on 24/7

kandm
March 3, 2009

My seedlings are just shy of 3 weeks old. Almost all have their first true leaves and several have their second true leaves. I have a 2 bulb t12 set up and I leave the lights on all the time. I turn a fan on them a few hours a day and they seem to be doing well. I have heard you shouldn't leave the lights on all the time like I'm doing and I wonder why not?

Does anyone know what will happen to seedlings if they are under the lights full time?

Comments (66)

  • wordwiz

    >> Wordwiz, is that getting moved outside? I'd do it quick before those blossoms get too big. You'll miss the initial growth phase that happens after transplant. Nah, it's going to live out its life in that bucket of water on that shelf.

    My hope is to get 25 pounds of tomatoes from it.

    Mike

  • ellmondo

    I suspect you will need to switch it to a 12/12 cycle after vegative stage/once maturity is reached. this is recommended for many plants grown under lights to start the fruiting stage.
    failure to do so could produce little to no yield and i feel this will happen in tomatoes from memory.

    I myself am also growing tomatoes under lights. It's going great for the new plant i just started. but unlike yours i will try the 12/12 stage when it is mature and will post my results so we can compare so more data aswell.

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  • macheske

    Elmondo,
    I have never intended to stay on 24 hours of light forever on these plants. These are starts that will go out to the garden. The question (I am/we are) trying to answer is whether 24/7 produces better starts than 16 hours of light. My contention is that 24 hours is better for starts using fluoresent lights especially considering that the amount of light is very small compared to the sun. Others have argued that they need a rest period each night, especially after week 7.
    Thanks,
    Rick

  • macheske

    Well, here is an update. The 24 hours plants are definitely larger and stronger looking.

    {{gwi:58904}}

    16 hour plant is on the left, 24 is on the right.
    Rick

  • wordwiz

    Rick,

    You are up to what... week eight now from when you started them? The difference is almost unbelievable!

    Mike

  • macheske

    Mike,
    Yes, it's been a little over 8 weeks (since Feb 1). I'm a little surprised as well. I noticed a large slow down in the 16 hour seedlings and didn't see the same in the 24 hour ones in the last couple weeks. Actually, the 24 hour seedlings have gotten so large that I expect to see a slowdown because they are shading each other too much now. Out of the two trays I'd say the 24 hour are on average about 2" taller than the 16 hour ones. Hopefully, they will be going into the garden in 2-3 weeks, depending on the weather.
    Rick

  • wordwiz

    Rick,

    To maintain the integrity of the test, could you move one or two of the larger plants to the 16 hour side?

    I would not have thought the differences would have been so significant but it's obvious they are!

    Mike

  • macheske

    Mike,
    I can do that. What would be the purpose?
    Thanks,
    Rick

  • wordwiz

    Rick,

    You posted: "Actually, the 24 hour seedlings have gotten so large that I expect to see a slowdown because they are shading each other too much now."

    If they slow down because they are shading each other then the benefits of 24/7 lighting might not be as apparent. The only drawback is you would not have as many plants to compare.

    Mike

  • macheske

    Mike,
    I'll move a few of the 24/7 seedlings to the 16 hour shelf. Then I'll space out some of the 24/7 seedlings. Unfortunately, I will only be able to do it for a few since I don't have much room on either shelf. Thanks for the suggestion.
    Rick

  • wordwiz

    Rick,

    Your experiment is going to be a hot topic in the Hot Pepper Forum. I'm also curious how the plants now going to 16 hrs. a day will compare to the ones that stay under the 24/7 set-up.

    Mike

  • zanderspice

    Rick,
    Very interesting experiment. One question; are the 16hr peppers in complete darkness for 8 hours or do they see some weak light from the other lamps? My technique has been 24/0 from seed, and sometimes 18/6 for a while before they go outside. My main motivation for the 6 hour dark period is to save some power and keep temps below 85 in the heat of the day.
    -Zander

  • macheske

    Mike,
    I'll try to draw some conclusions on the ones that are now on the 16 hour shelf that were on the 24 hour shelf.

    Zander,
    They don't get "complete" darkness during the dark period. The top shelf is the one that I went to 16 hours on so it's not much though. At least it's very inderect light that they might get.

  • macheske

    Well, I just wanted to provide an update on the 24 hour experiment. All of the peppers are starting the hardening off process now so the indoor part of the experiment is over. They are now in a fairly sheltered place outside and will only be moved inside if temperatures drop below 38 degrees at night. I found a great way to harden them off last year. Since I have a large trailer that I use to move my tractor when needed I just put them all on the trailer and move the trailer to a place with more and more light until they are fully hardened off. Ok..the results.

    The 24 hour peppers definitely look better. They look like they are a few weeks ahead of the 16 hour peppers. I'd say on average they are about 2" taller and have thicker stems. Some already are flowering and are probably past overdue to get in the garden. I'll mark them this summer and see if I can tell any difference in the yield or how fast they produce fruit. As expected there are some in the middle of the flats that were not getting enough light because they were pretty densely packed in 3" pots.

    Overall, I'd have to say that 24 hour light is great for seedlings.
    Rick

  • llbean

    Rick~
    Can I ask at what height you had your lights? This is the first year that I have put it chains to adjust my lights. I can try to post a picture of my set up later. I have always used 24 hour light (due to laziness to get a timer) but this year with lowering the lights I have had better growth. Thing is, I started them in a "DOME" with plugs, quickly they out grew the dome and plugs, I moved to three inch pots, but left them in the dome for moisture sake. Thing is the "DOME" is large and the lights above needed to be the height of the dome, so now my Tomato's are looking a bit leggy. should I uncap the dome and lower my lights?
    Again I will try to post a picture a bit later...
    I appreciate any one's help and feedback.
    L

  • macheske

    L,
    I keep the lights 1 to 2 inches above the plants. Often the lights are touching the plants because they grow so fast. I do it by adjusting chains as well. I use a clear plastic cover until I get the first sprout in the tray and then take it off. I'm assuming thats what you mean by dome. Sounds like you should lower the lights ASAP.
    Rick

  • llbean

    Rick~

    Thanks.. Yes a certain seed company sells a Dome... that is what I use.
    I have used the dome after sprouting becuase it helps with the moisture. I also use heat to start things off.
    I probably started to late, but here in Michigan you never know when you can plant :) it snowed here last week, after 5 days of sun...
    I will lower the lights today. I was thinking that they should not touch because they may burn but I will lower.
    Laura

  • Karen Pease

    Let your hand be a judge. If a light of any kind feels hot to your fingers at the distance the plants will be, it's probably too close. Comfortably warm is just fine, though.

  • wordwiz

    Regular shop lights will not burn the leaves. I've actually had leaves almost curl around the bulbs before.

    Rick,

    Great job! I look forward to your end of the year results.

    Mike

  • hooked_on_ponics

    Very interesting, I recently read something about this somewhere else, and I heard from someone that Advanced Nutrients did a study that showed 24/7 lighting out-performed other schedules in plant growth.

    But I think it makes a lot of difference what kind of plant you're talking about. If a plant is triggered to produce fruit based upon light cycle, too much light wouldn't necessarily be a good thing.

    Plus you have to think about the electric bill. If you're not running very many or very big lights it might not make much difference, but if you've turned your home into a greenhouse it could cost a lot to run the lights all the time.

    I'm very interested in seeing how those pepper plants turn out.

  • barbaraincalif

    New reader here...great thread!
    Would using a timer to cycle your lights on and off save money on electricty, while still effectively providing 24/7 light?

    Barbara

  • wordwiz

    Barbara,

    ??????

    If you run the lights 24 hours a day, seven days a week, why would you need a timer to turn them on or off?

    Mike

  • barbaraincalif

    Sorry...bad explanation on my part. I'm starting cuttings in an outdoor shed where heat build-up is a concern during the day. I started cycling the lights on and off in 30 minute intervals during their 16 hour day...which effectively uses 1/2 the ammount of electricty while helping keep the propagation area cooler. There have been no adverse effects in shoot growth that I can see.

    I'm suggesting there may be cost saving ways to achieve a 24hour light cycle that are worth a try.

    Barbara

  • Karen Pease

    On the subject of "dark" (i.e., for plants that need long nights to flower, or whatnot)... how dark is "dark"? How much light does it take to disrupt a plant's internal timer?

  • klinko16

    24/7 Henry Kuska posted about this before. He floods his seedlings 24/7. I flood my rose cuttings 24/7. They grow nice and big, also if you are using fluorescent, the lamps last longer and have stronger output (even though this might be only marginal, it is still true) if they are on 24.7. Plus you maximize the output for your facility. Some people claim the plant needs to "rest", but this is not true, it only needs a dark period if it is photoperiodic, and for ourselves, we are
    talking about VEGETATIVE phase, I assume. A PHOTOPERIODIC plant REQUIRES dark, in order for the flowering hormones (Pyr Pyfr) to mature and trigger flowering.
    What Henry pointed out is that CYCLING OF TEMPERATURE can be important, when the lights are on 24/7, some plants do better if there is a cooling down time.

  • macheske

    Just a quick update. The pepper plants that were given 24/7 light are already starting to produce! They are definitely larger and healthier looking. That's way ahead of last year and even ahead of my tomatoes. The 16 hour plants are definitely behind.

    {{gwi:70914}}

  • xmaslightguy

    Truly amazing how good the 24/7 light plants look, definitely
    a interesting experiment you did...thanks for posting &
    keeping it updated!

    I've always given the plants 12 hours of light per day when
    starting seeds for the garden...they grow ok but maybe
    thats not enough?

    my houseplants get 10 hours (plus whatever sunlight comes
    in through the north-facing window...which in the winter
    is less than 10 hours)

  • wordwiz

    Hey macheske,

    Any updates? Can you still tell the difference?

    Mike

  • macheske

    Mike,
    I can definitely tell the difference. The 24/7 plants have almost all produced picking sized peppers already. I have a drawer full in the fridge. They are also putting on a second set of peppers that are about the same size as the 16 hour peppers. The only picking sized peppers from the 16 hour group are jalapenos and those are 42 picked from the 24/7 plants and 3 from the 16 hour plants. It looks like I'm going to get an extra crop from the 24/7 peppers. I think I have enough information to call the 24/7 peppers a big sucess.
    Rick

  • shawnann

    New to the conversation...
    Rick this experiment was interesting. You mentioned that the pepper plant was even ahead of your tomatoes...how much light did you give your tomatoes? Did you start them at the same time? I like to grow both peppers and tomatoes and I sure would like to be picking some in June next year. I am still waiting with only blooms so far.

    Thanks for posting all of this and the pics!
    My Garden Blog

  • macheske

    Shawn Ann,
    Your garden looks great! In upper zone 6 you're way ahead. I'm getting a couple of pounds of beans a day and a lot of peppers but that's about it for now. The cucumbers will be ready to start to pick in a couple of days and the tomatoes are just started. I picked the first Sungold today. We should have our first large tomato in about a week. We're also getting summer squash and zucchini. I don't think we have any watermellons forming yet. I'll have to check. The tomato plants were under 16 hour light this year. Next year they will be under 24 hour light but started a little later.

    Congrats on the new little one.
    Rick

  • klinko16

    I'm glad you schooled everyone in the benefits of 24/7. I personally run 24/7 on my roses, and the growth is absolutely phenomenal. The only reason to run a night cycle, is for (in my experience) to grow cuttings. When cuttings have no roots, they cannot make use of 24/7 illumination. using 16/8 cycle allows for a cooling period and a dark period which may be of benefit to INITIATE roots (not grow roots - roots grow all the time). Also, for cannabis, in vegetative phase, 24/7 is also the way to go for a much bigger and heavier harvest, and nicer smoke, with very nice strong high.

  • shawnann

    Thanks Rick! And I thought I was behind...guess it is all where you are at. I can't wait to experiment with the tomatoes and peppers next winter/spring. We'll see what happens.

    Happy gardening!
    My Garden Blog

  • gringojay

    Plez, let us also hear at the end of the season how the 24/7 plants total pepper yield seems to have been....

  • john_z11

    ...so was that the final word, any up-dates?

  • wood7932

    Why why why. The picture indicates the plant with 24hr lighting is visibly larger, but a picture alone at this stage of growth is a somewhat poor indication of actual plant health. Just turn your lights off at night like everyone else and save electricity. FYI whoever thinks Alaska plants benefit from extended periods of daylight should think again, the extended light periods experienced during the summer season do not supply as many lumens as you might think.

  • wordwiz

    wood,

    The plants did grow quicker, I followed his thread throughout last spring. And while there may not be an advantage to 24/7 if one has plenty of time to get the seedlings large enough, it is a huge benefit if time is short.

    Mike

  • elkwc

    I would like to see any updates. Interesting reading and what I've read and been told by several growers who have researched and experimented with 24 hour lighting. I had some I got started this year 7-10 days late. They have been under 24 hours lights for 11 days and have caught and starting to pass those 7-10 days older. I have them all under 24 hours lights now. From what I'm seeing the light bill won't be a lot difference because they are growing fast enough I will be able to move them to the cold frames and start hardening off sooner. If you had a greenhouse and wanted some growth before moving there it would work well also. I feel I will move them outside and turn the light shelves off 7-10 days earlier than normal. So the money I save there will offset some of the cost of keeping them on 24 hours straight. Again interested in all updates. Jay

  • wordwiz

    Jay,

    I'm doing a test - out of necessity! I've got to get large enough tomato plants ready to transplant in no more than five weeks - from sowing the seeds. I started a thread about it.

    Mike

  • veriria

    Would having the lights on 24/7 work for most if not all plants, or are there some that definitely need no-light time?

  • lori_ny

    "Regular shop lights will not burn the leaves. I've actually had leaves almost curl around the bulbs before. "

    Do plants grow as well with shop lights? Are those lights that are basic fluorescent bulbs and not growing bulbs?

  • xFozzyx

    The problem with how you tested 16/8 and 24/7 is that you are not using enough light.

    At proper light levels & 24/7 lighting things will go badly. Sugars/energy will build up in the tops of the plant in a solid form and will not be mobile or usable to the plant. the amount of Fruit set will be lower and the quality will be much worse.

    At the lower light levels it just so happends the 24/7 plants were just less abused than the 16/8 plants.

    & depending on how well you set up the experiment could have made a big difference.... Did you light seal the room? ANY light over ~ 5lumens? that gets to the plants (at night time) the phytochrome a/b (what a plant uses to judge how much day or night time over the day it has had is instantly converted and the cycle must start again.

  • Peter (6b SE NY)

    What's the current wisdom, is it ok to leave the lights on 24/7 for seedlings, or give them an irregular lighting cycle? I think the day/night cycle is more of an issue for full size flowering plants, or seedlings getting full sun, and it is perfectly fine for indoor seed starting to leave the grow lights on 24/7, correct?

  • in ny zone5

    The above picture shows the initial domed seed trays in November 2014. I commented elsewhere that I am growing hosta seedlings under fluorescent lights since middle of November 24 hrs each day. Some of my seedlings are shown in the Hosta Forum in the Seedlings thread. I will bring them outside in May. Common 4ft fuorescent lights were 1 inch above domes and are now 1 inch above tallest leaves of plants. All light gets reflected back to plants with aluminum foil covered cardboard, not shown yet above. I am doing this now the 4th year and have seen no problems. Another benefit is that the heat generated by the lights is enough to germinate under domes at 81 dgrs and grow the plants thereafter without domes at 71 dgrs in my 60 dgrs basement. I created enclosed growing chambers on my 2 shelves by enclosing above shelves with 2 walls (behind and right) and old towels (left and front). I no longer use my heating mat.

  • GuruAvtar Khalsa

    I'm from Alaska and have experience growing food in natural 24/7 sunlight, not under grow lights. The plants absolutely love it. They grow bigger, stronger, quicker, and production doesn't ever seem to be an issue. The only question I have is "does this affect the nutrient contents in any way?" This is something I've debated before but have no real knowledge about. I don't see why it would alter the nutrient content as most of that has to do with the soil not the sun. The sun does have a part in it, but how might more sunlight create less nutrients?

    I can answer that everything I have ever seen grown in 24/7 light loves it and never shows any I'll affect from this treatment. This goes for both seedlings and full size plants getting ready to fruit or already fruiting.

  • aruzinsky

    One consequence of leaving the lights on is that you lose the opportunity to grow extra short plants by making the dark period temperature higher than the light period temperature.

  • pepper_rancher

    zomg, I cant see any of the pictures! Can you re-host them or is it just me?


  • annythraxx

    I love this thread. I have a lemon tree I started from seed Dec2015 that I used 24/7 light on until I put it outside in the spring. Now it's Nov 2016 and I have it under a LED grow light 24/7 and the leaves are much more large than full sun outside and it's growing faster inside. When I started it from seed I used a basic fluorescent day light lamp bulb. I go to other garden sites and lord help me if I ever mention I use 24/7 light because everyone tells me that's bad for all of your plants ... Uh well I have had nothing but faster growth and no problems. I also have a prayer plant under my 24/7. It has done way better even though they fold up at night...mine don't move but they are growing way faster and much better. I had taken some clippings of a prayer plant that were getting root rot. I cut them and forced them to re root and stay under the light and they formed roots extremely quick and are pushing out new leaves and seem perfectly happy. I find it very helpfull for low light plants to just be farther away from it and my high light lemon tree closer to it. Works beautifully.

  • toddkarrick

    If I already have my tomatoes on 24 hrs of light. Can I back that off a lil at a time ? Light bill is high !

  • LoneJack Zn 6a, KC

    Todd - yes you can. I would back the lights off about 2 hours a day until you get down to 16 hours on, 8 off.

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