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Is Darkness Necessary?

North West, OH(Zone 5b)

Even as I typed that it sounded absurd, but maybe the darkness has a purpose too. Last year I started all my seedlings under a shop light with great success, but I never turned it off. Ever. I keep seeing people recommend X amount of hours with the light on and X amount of hours with it turned off. Is there an actual reason for turning the light off or are they simply just stating what the minimum requirements are? As I said, mine have done beautifully so far with light 24/7 (knock on wood), but could they be doing even better?

Thanks all.....What a delight this forum is!

Columbus, OH

The ideal number of hours for light ranges between 12-16, so they say, with an 8 hour period of rest or dormancy. I agree with you that sometimes 24/7 doesn't hurt. I've left mine on by accident over night and found they were fine the next morning - a bit dry, but fine. In all honesty, I think it IS probably best to try and imitate the normal day/night cycle just so your seedlings get acclimated to "the real world" asap. Hope this helps. Howard.

Dublin, CA(Zone 9a)

I always turn mine off at night, never tried doing it any other way so I don't know if it makes a difference or not. I have mine set up on an automatic timer so I don't have to worry about remembering to turn the lights on or off.

Port Orchard, WA(Zone 8a)

La, I'm doing my seeds and seedlings 16/8, but I know people that do 24 with great success. I'm thinking costs. I have 12 shop lights going on my seeds and seedlings. Jim

Byron, GA

I leave mine on 24/7, also. However, our winters are milder and shorter so the seedlings don't stay under the lights very long. As soon as they can be transplanted, I move them outside with protection where they get what sunlight is available leaving space to start more seeds under lights. I guess leaving the lights on 24/7 is like Alaskan conditions in the summer. I'm sure that long term exposure would affect the plant's metabolism and flowering cycle.


(Zone 4a)

Two different subjects here: 1. Darkness for seed germination;

2. Seedling light requirements.

Some seeds require darkness for germination. These containers/baggies should be kept
in a dark cupboard, etc., until germination. The temperature for germination should be
considered, too.

North West, OH(Zone 5b)

Thanks for all the imput. I do start my seed according to it's light requirements, but it was the seedlings themselves I was wondering about. Maybe I'll experiment a little and try turning the light off at night (if I can remember, LOL). I only have 3 lights going so I doubt it makes that much difference in electricity, but I'm always up for trying something different.


Byron, GA

I start my tomato and peppers in the dark until I see the first sprout coming through the soil. Then they get the light treatment. I put them as close as I can to the light. Thanks taramark for the gentle reminder to clarify.

Elmira, NY(Zone 6a)

There is a purpose for the darkness with seedlings. They put on a different type of growth in the dark than they do in the light. There's a name for it, but I forget what it is. Not many plants enjoy 24/7 light. If you alternate between dark and light, you will see sturdier growth.

Eastlake, OH(Zone 5a)

The whole purpose for certain amount of light hours and a certain amount of darkness is so the plants can set buds. When the plants are young seedlings, you don't have to worry about that. Once they devlope their true leaves, you must give them the right amount of daylight and the correct amount of darkness. Not all plants require 16 of hours of light. Some require shorter days. Keeping that in mind, you might end up with nothing but foliage with 24 hours of light during the whole plant life growing period.

North West, OH(Zone 5b)

Wow, who'da thought? Well I suppose a lot of you'da thought, LOL. But for this rookie this has been an eye-opener. I'm sure glad I posted this question as I'm sure it has been a big help to many of us newbies. Thanks a million!

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